src/audio/SDL_audiocvt.c
author Aaron Wishnick <schnarf@gmail.com>
Wed, 02 Jul 2008 08:04:50 +0000
branchgsoc2008_audio_resampling
changeset 2661 d38309be5178
parent 2660 a55543cef395
child 2662 5470680ca587
permissions -rw-r--r--
The windowed sinc filter generation code seems to be working fine. The FIR filtering code is also now working reasonably well. Occasionally the FIR filter will pop, but setting the normalization factor lower seems to help this. I suspect the problem is in the fixed point multiply/add. I also have a hunch the zero stuffing/sample discarding code is not correct, and I'll look at that soon to get it sorted out.

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2006 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"
#include <math.h>

/* Functions for audio drivers to perform runtime conversion of audio format */

#include "SDL_audio.h"
#include "SDL_audio_c.h"

#define DEBUG_CONVERT

/* Perform fractional multiplication of two 32-bit integers to produce a 32-bit result. Assumes sizeof(long) = 4 */
/*#define SDL_FixMpy32(v1, v2, dest) { \
			long a, b, c, d; \
			long x, y; \
			a = (v1 >> 16) & 0xffff; \
			b = v1 & 0xffff; \
			c = (v2 >> 16); \
			d = v2 & 0xffff; \
			x = a * d + c * b; \
			y = (((b*d) >> 16) & 0xffff) + x; \
			dest = ((y >> 16) & 0xffff) + (a * c); \
		}*/
/* TODO: Check if 64-bit type exists. If not, see http://www.8052.com/mul16.phtml or http://www.cs.uaf.edu/~cs301/notes/Chapter5/node5.html */

/* We hope here that the right shift includes sign extension */
#ifdef SDL_HAS_64BIT_Type		
#define SDL_FixMpy32(a, b) ((((Sint64)a * (Sint64)b) >> 31) & 0xffffffff)
#else
/* need to do something more complicated here */
#define SDL_FixMpy32(a, b) ((((Sint64)a * (Sint64)b) >> 31) & 0xffffffff)
#endif
/* Confirmed that SDL_FixMpy16 works, need to check 8 and 32 */
#define SDL_FixMpy16(a, b) ((((Sint32)a * (Sint32)b) >> 14) & 0xffff)
#define SDL_FixMpy8(a, b) ((((Sint16)a * (Sint16)b) >> 7) & 0xff)
/* Everything is signed! */
#define SDL_Make_1_7(a) (Sint8)(a * 127.0f)
#define SDL_Make_1_15(a) (Sint16)(a * 32767.0f)
#define SDL_Make_1_31(a) (Sint32)(a * 2147483647.0f)
#define SDL_Make_2_6(a) (Sint8)(a * 63.0f)
#define SDL_Make_2_14(a) (Sint16)(a * 16383.0f)
#define SDL_Make_2_30(a) (Sint32)(a * 1073741823.0f)

/* Effectively mix right and left channels into a single channel */
static void SDLCALL
SDL_ConvertMono(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;
    Sint32 sample;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting to mono\n");
#endif
    switch (format & (SDL_AUDIO_MASK_SIGNED | SDL_AUDIO_MASK_BITSIZE)) {
    case AUDIO_U8:
        {
            Uint8 *src, *dst;

            src = cvt->buf;
            dst = cvt->buf;
            for (i = cvt->len_cvt / 2; i; --i) {
                sample = src[0] + src[1];
                *dst = (Uint8) (sample / 2);
                src += 2;
                dst += 1;
            }
        }
        break;

    case AUDIO_S8:
        {
            Sint8 *src, *dst;

            src = (Sint8 *) cvt->buf;
            dst = (Sint8 *) cvt->buf;
            for (i = cvt->len_cvt / 2; i; --i) {
                sample = src[0] + src[1];
                *dst = (Sint8) (sample / 2);
                src += 2;
                dst += 1;
            }
        }
        break;

    case AUDIO_U16:
        {
            Uint8 *src, *dst;

            src = cvt->buf;
            dst = cvt->buf;
            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    sample = (Uint16) ((src[0] << 8) | src[1]) +
                        (Uint16) ((src[2] << 8) | src[3]);
                    sample /= 2;
                    dst[1] = (sample & 0xFF);
                    sample >>= 8;
                    dst[0] = (sample & 0xFF);
                    src += 4;
                    dst += 2;
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    sample = (Uint16) ((src[1] << 8) | src[0]) +
                        (Uint16) ((src[3] << 8) | src[2]);
                    sample /= 2;
                    dst[0] = (sample & 0xFF);
                    sample >>= 8;
                    dst[1] = (sample & 0xFF);
                    src += 4;
                    dst += 2;
                }
            }
        }
        break;

    case AUDIO_S16:
        {
            Uint8 *src, *dst;

            src = cvt->buf;
            dst = cvt->buf;
            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    sample = (Sint16) ((src[0] << 8) | src[1]) +
                        (Sint16) ((src[2] << 8) | src[3]);
                    sample /= 2;
                    dst[1] = (sample & 0xFF);
                    sample >>= 8;
                    dst[0] = (sample & 0xFF);
                    src += 4;
                    dst += 2;
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    sample = (Sint16) ((src[1] << 8) | src[0]) +
                        (Sint16) ((src[3] << 8) | src[2]);
                    sample /= 2;
                    dst[0] = (sample & 0xFF);
                    sample >>= 8;
                    dst[1] = (sample & 0xFF);
                    src += 4;
                    dst += 2;
                }
            }
        }
        break;

    case AUDIO_S32:
        {
            const Uint32 *src = (const Uint32 *) cvt->buf;
            Uint32 *dst = (Uint32 *) cvt->buf;
            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 8; i; --i, src += 2) {
                    const Sint64 added =
                        (((Sint64) (Sint32) SDL_SwapBE32(src[0])) +
                         ((Sint64) (Sint32) SDL_SwapBE32(src[1])));
                    *(dst++) = SDL_SwapBE32((Uint32) ((Sint32) (added / 2)));
                }
            } else {
                for (i = cvt->len_cvt / 8; i; --i, src += 2) {
                    const Sint64 added =
                        (((Sint64) (Sint32) SDL_SwapLE32(src[0])) +
                         ((Sint64) (Sint32) SDL_SwapLE32(src[1])));
                    *(dst++) = SDL_SwapLE32((Uint32) ((Sint32) (added / 2)));
                }
            }
        }
        break;

    case AUDIO_F32:
        {
            const float *src = (const float *) cvt->buf;
            float *dst = (float *) cvt->buf;
            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 8; i; --i, src += 2) {
                    const float src1 = SDL_SwapFloatBE(src[0]);
                    const float src2 = SDL_SwapFloatBE(src[1]);
                    const double added = ((double) src1) + ((double) src2);
                    const float halved = (float) (added * 0.5);
                    *(dst++) = SDL_SwapFloatBE(halved);
                }
            } else {
                for (i = cvt->len_cvt / 8; i; --i, src += 2) {
                    const float src1 = SDL_SwapFloatLE(src[0]);
                    const float src2 = SDL_SwapFloatLE(src[1]);
                    const double added = ((double) src1) + ((double) src2);
                    const float halved = (float) (added * 0.5);
                    *(dst++) = SDL_SwapFloatLE(halved);
                }
            }
        }
        break;
    }

    cvt->len_cvt /= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Discard top 4 channels */
static void SDLCALL
SDL_ConvertStrip(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting down from 6 channels to stereo\n");
#endif

#define strip_chans_6_to_2(type) \
    { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 6); i; --i) { \
            dst[0] = src[0]; \
            dst[1] = src[1]; \
            src += 6; \
            dst += 2; \
        } \
    }

    /* this function only cares about typesize, and data as a block of bits. */
    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        strip_chans_6_to_2(Uint8);
        break;
    case 16:
        strip_chans_6_to_2(Uint16);
        break;
    case 32:
        strip_chans_6_to_2(Uint32);
        break;
    }

#undef strip_chans_6_to_2

    cvt->len_cvt /= 3;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Discard top 2 channels of 6 */
static void SDLCALL
SDL_ConvertStrip_2(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting 6 down to quad\n");
#endif

#define strip_chans_6_to_4(type) \
    { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 6); i; --i) { \
            dst[0] = src[0]; \
            dst[1] = src[1]; \
            dst[2] = src[2]; \
            dst[3] = src[3]; \
            src += 6; \
            dst += 4; \
        } \
    }

    /* this function only cares about typesize, and data as a block of bits. */
    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        strip_chans_6_to_4(Uint8);
        break;
    case 16:
        strip_chans_6_to_4(Uint16);
        break;
    case 32:
        strip_chans_6_to_4(Uint32);
        break;
    }

#undef strip_chans_6_to_4

    cvt->len_cvt /= 6;
    cvt->len_cvt *= 4;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Duplicate a mono channel to both stereo channels */
static void SDLCALL
SDL_ConvertStereo(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting to stereo\n");
#endif

#define dup_chans_1_to_2(type) \
    { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + cvt->len_cvt * 2); \
        for (i = cvt->len_cvt / 2; i; --i, --src) { \
            const type val = *src; \
            dst -= 2; \
            dst[0] = dst[1] = val; \
        } \
    }

    /* this function only cares about typesize, and data as a block of bits. */
    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        dup_chans_1_to_2(Uint8);
        break;
    case 16:
        dup_chans_1_to_2(Uint16);
        break;
    case 32:
        dup_chans_1_to_2(Uint32);
        break;
    }

#undef dup_chans_1_to_2

    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Duplicate a stereo channel to a pseudo-5.1 stream */
static void SDLCALL
SDL_ConvertSurround(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting stereo to surround\n");
#endif

    switch (format & (SDL_AUDIO_MASK_SIGNED | SDL_AUDIO_MASK_BITSIZE)) {
    case AUDIO_U8:
        {
            Uint8 *src, *dst, lf, rf, ce;

            src = (Uint8 *) (cvt->buf + cvt->len_cvt);
            dst = (Uint8 *) (cvt->buf + cvt->len_cvt * 3);
            for (i = cvt->len_cvt; i; --i) {
                dst -= 6;
                src -= 2;
                lf = src[0];
                rf = src[1];
                ce = (lf / 2) + (rf / 2);
                dst[0] = lf;
                dst[1] = rf;
                dst[2] = lf - ce;
                dst[3] = rf - ce;
                dst[4] = ce;
                dst[5] = ce;
            }
        }
        break;

    case AUDIO_S8:
        {
            Sint8 *src, *dst, lf, rf, ce;

            src = (Sint8 *) cvt->buf + cvt->len_cvt;
            dst = (Sint8 *) cvt->buf + cvt->len_cvt * 3;
            for (i = cvt->len_cvt; i; --i) {
                dst -= 6;
                src -= 2;
                lf = src[0];
                rf = src[1];
                ce = (lf / 2) + (rf / 2);
                dst[0] = lf;
                dst[1] = rf;
                dst[2] = lf - ce;
                dst[3] = rf - ce;
                dst[4] = ce;
                dst[5] = ce;
            }
        }
        break;

    case AUDIO_U16:
        {
            Uint8 *src, *dst;
            Uint16 lf, rf, ce, lr, rr;

            src = cvt->buf + cvt->len_cvt;
            dst = cvt->buf + cvt->len_cvt * 3;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 12;
                    src -= 4;
                    lf = (Uint16) ((src[0] << 8) | src[1]);
                    rf = (Uint16) ((src[2] << 8) | src[3]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[1] = (lf & 0xFF);
                    dst[0] = ((lf >> 8) & 0xFF);
                    dst[3] = (rf & 0xFF);
                    dst[2] = ((rf >> 8) & 0xFF);

                    dst[1 + 4] = (lr & 0xFF);
                    dst[0 + 4] = ((lr >> 8) & 0xFF);
                    dst[3 + 4] = (rr & 0xFF);
                    dst[2 + 4] = ((rr >> 8) & 0xFF);

                    dst[1 + 8] = (ce & 0xFF);
                    dst[0 + 8] = ((ce >> 8) & 0xFF);
                    dst[3 + 8] = (ce & 0xFF);
                    dst[2 + 8] = ((ce >> 8) & 0xFF);
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 12;
                    src -= 4;
                    lf = (Uint16) ((src[1] << 8) | src[0]);
                    rf = (Uint16) ((src[3] << 8) | src[2]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[0] = (lf & 0xFF);
                    dst[1] = ((lf >> 8) & 0xFF);
                    dst[2] = (rf & 0xFF);
                    dst[3] = ((rf >> 8) & 0xFF);

                    dst[0 + 4] = (lr & 0xFF);
                    dst[1 + 4] = ((lr >> 8) & 0xFF);
                    dst[2 + 4] = (rr & 0xFF);
                    dst[3 + 4] = ((rr >> 8) & 0xFF);

                    dst[0 + 8] = (ce & 0xFF);
                    dst[1 + 8] = ((ce >> 8) & 0xFF);
                    dst[2 + 8] = (ce & 0xFF);
                    dst[3 + 8] = ((ce >> 8) & 0xFF);
                }
            }
        }
        break;

    case AUDIO_S16:
        {
            Uint8 *src, *dst;
            Sint16 lf, rf, ce, lr, rr;

            src = cvt->buf + cvt->len_cvt;
            dst = cvt->buf + cvt->len_cvt * 3;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 12;
                    src -= 4;
                    lf = (Sint16) ((src[0] << 8) | src[1]);
                    rf = (Sint16) ((src[2] << 8) | src[3]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[1] = (lf & 0xFF);
                    dst[0] = ((lf >> 8) & 0xFF);
                    dst[3] = (rf & 0xFF);
                    dst[2] = ((rf >> 8) & 0xFF);

                    dst[1 + 4] = (lr & 0xFF);
                    dst[0 + 4] = ((lr >> 8) & 0xFF);
                    dst[3 + 4] = (rr & 0xFF);
                    dst[2 + 4] = ((rr >> 8) & 0xFF);

                    dst[1 + 8] = (ce & 0xFF);
                    dst[0 + 8] = ((ce >> 8) & 0xFF);
                    dst[3 + 8] = (ce & 0xFF);
                    dst[2 + 8] = ((ce >> 8) & 0xFF);
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 12;
                    src -= 4;
                    lf = (Sint16) ((src[1] << 8) | src[0]);
                    rf = (Sint16) ((src[3] << 8) | src[2]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[0] = (lf & 0xFF);
                    dst[1] = ((lf >> 8) & 0xFF);
                    dst[2] = (rf & 0xFF);
                    dst[3] = ((rf >> 8) & 0xFF);

                    dst[0 + 4] = (lr & 0xFF);
                    dst[1 + 4] = ((lr >> 8) & 0xFF);
                    dst[2 + 4] = (rr & 0xFF);
                    dst[3 + 4] = ((rr >> 8) & 0xFF);

                    dst[0 + 8] = (ce & 0xFF);
                    dst[1 + 8] = ((ce >> 8) & 0xFF);
                    dst[2 + 8] = (ce & 0xFF);
                    dst[3 + 8] = ((ce >> 8) & 0xFF);
                }
            }
        }
        break;

    case AUDIO_S32:
        {
            Sint32 lf, rf, ce;
            const Uint32 *src = (const Uint32 *) cvt->buf + cvt->len_cvt;
            Uint32 *dst = (Uint32 *) cvt->buf + cvt->len_cvt * 3;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 6;
                    src -= 2;
                    lf = (Sint32) SDL_SwapBE32(src[0]);
                    rf = (Sint32) SDL_SwapBE32(src[1]);
                    ce = (lf / 2) + (rf / 2);
                    dst[0] = SDL_SwapBE32((Uint32) lf);
                    dst[1] = SDL_SwapBE32((Uint32) rf);
                    dst[2] = SDL_SwapBE32((Uint32) (lf - ce));
                    dst[3] = SDL_SwapBE32((Uint32) (rf - ce));
                    dst[4] = SDL_SwapBE32((Uint32) ce);
                    dst[5] = SDL_SwapBE32((Uint32) ce);
                }
            } else {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 6;
                    src -= 2;
                    lf = (Sint32) SDL_SwapLE32(src[0]);
                    rf = (Sint32) SDL_SwapLE32(src[1]);
                    ce = (lf / 2) + (rf / 2);
                    dst[0] = src[0];
                    dst[1] = src[1];
                    dst[2] = SDL_SwapLE32((Uint32) (lf - ce));
                    dst[3] = SDL_SwapLE32((Uint32) (rf - ce));
                    dst[4] = SDL_SwapLE32((Uint32) ce);
                    dst[5] = SDL_SwapLE32((Uint32) ce);
                }
            }
        }
        break;

    case AUDIO_F32:
        {
            float lf, rf, ce;
            const float *src = (const float *) cvt->buf + cvt->len_cvt;
            float *dst = (float *) cvt->buf + cvt->len_cvt * 3;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 6;
                    src -= 2;
                    lf = SDL_SwapFloatBE(src[0]);
                    rf = SDL_SwapFloatBE(src[1]);
                    ce = (lf * 0.5f) + (rf * 0.5f);
                    dst[0] = src[0];
                    dst[1] = src[1];
                    dst[2] = SDL_SwapFloatBE(lf - ce);
                    dst[3] = SDL_SwapFloatBE(rf - ce);
                    dst[4] = dst[5] = SDL_SwapFloatBE(ce);
                }
            } else {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 6;
                    src -= 2;
                    lf = SDL_SwapFloatLE(src[0]);
                    rf = SDL_SwapFloatLE(src[1]);
                    ce = (lf * 0.5f) + (rf * 0.5f);
                    dst[0] = src[0];
                    dst[1] = src[1];
                    dst[2] = SDL_SwapFloatLE(lf - ce);
                    dst[3] = SDL_SwapFloatLE(rf - ce);
                    dst[4] = dst[5] = SDL_SwapFloatLE(ce);
                }
            }
        }
        break;

    }
    cvt->len_cvt *= 3;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Duplicate a stereo channel to a pseudo-4.0 stream */
static void SDLCALL
SDL_ConvertSurround_4(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting stereo to quad\n");
#endif

    switch (format & (SDL_AUDIO_MASK_SIGNED | SDL_AUDIO_MASK_BITSIZE)) {
    case AUDIO_U8:
        {
            Uint8 *src, *dst, lf, rf, ce;

            src = (Uint8 *) (cvt->buf + cvt->len_cvt);
            dst = (Uint8 *) (cvt->buf + cvt->len_cvt * 2);
            for (i = cvt->len_cvt; i; --i) {
                dst -= 4;
                src -= 2;
                lf = src[0];
                rf = src[1];
                ce = (lf / 2) + (rf / 2);
                dst[0] = lf;
                dst[1] = rf;
                dst[2] = lf - ce;
                dst[3] = rf - ce;
            }
        }
        break;

    case AUDIO_S8:
        {
            Sint8 *src, *dst, lf, rf, ce;

            src = (Sint8 *) cvt->buf + cvt->len_cvt;
            dst = (Sint8 *) cvt->buf + cvt->len_cvt * 2;
            for (i = cvt->len_cvt; i; --i) {
                dst -= 4;
                src -= 2;
                lf = src[0];
                rf = src[1];
                ce = (lf / 2) + (rf / 2);
                dst[0] = lf;
                dst[1] = rf;
                dst[2] = lf - ce;
                dst[3] = rf - ce;
            }
        }
        break;

    case AUDIO_U16:
        {
            Uint8 *src, *dst;
            Uint16 lf, rf, ce, lr, rr;

            src = cvt->buf + cvt->len_cvt;
            dst = cvt->buf + cvt->len_cvt * 2;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 8;
                    src -= 4;
                    lf = (Uint16) ((src[0] << 8) | src[1]);
                    rf = (Uint16) ((src[2] << 8) | src[3]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[1] = (lf & 0xFF);
                    dst[0] = ((lf >> 8) & 0xFF);
                    dst[3] = (rf & 0xFF);
                    dst[2] = ((rf >> 8) & 0xFF);

                    dst[1 + 4] = (lr & 0xFF);
                    dst[0 + 4] = ((lr >> 8) & 0xFF);
                    dst[3 + 4] = (rr & 0xFF);
                    dst[2 + 4] = ((rr >> 8) & 0xFF);
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 8;
                    src -= 4;
                    lf = (Uint16) ((src[1] << 8) | src[0]);
                    rf = (Uint16) ((src[3] << 8) | src[2]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[0] = (lf & 0xFF);
                    dst[1] = ((lf >> 8) & 0xFF);
                    dst[2] = (rf & 0xFF);
                    dst[3] = ((rf >> 8) & 0xFF);

                    dst[0 + 4] = (lr & 0xFF);
                    dst[1 + 4] = ((lr >> 8) & 0xFF);
                    dst[2 + 4] = (rr & 0xFF);
                    dst[3 + 4] = ((rr >> 8) & 0xFF);
                }
            }
        }
        break;

    case AUDIO_S16:
        {
            Uint8 *src, *dst;
            Sint16 lf, rf, ce, lr, rr;

            src = cvt->buf + cvt->len_cvt;
            dst = cvt->buf + cvt->len_cvt * 2;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 8;
                    src -= 4;
                    lf = (Sint16) ((src[0] << 8) | src[1]);
                    rf = (Sint16) ((src[2] << 8) | src[3]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[1] = (lf & 0xFF);
                    dst[0] = ((lf >> 8) & 0xFF);
                    dst[3] = (rf & 0xFF);
                    dst[2] = ((rf >> 8) & 0xFF);

                    dst[1 + 4] = (lr & 0xFF);
                    dst[0 + 4] = ((lr >> 8) & 0xFF);
                    dst[3 + 4] = (rr & 0xFF);
                    dst[2 + 4] = ((rr >> 8) & 0xFF);
                }
            } else {
                for (i = cvt->len_cvt / 4; i; --i) {
                    dst -= 8;
                    src -= 4;
                    lf = (Sint16) ((src[1] << 8) | src[0]);
                    rf = (Sint16) ((src[3] << 8) | src[2]);
                    ce = (lf / 2) + (rf / 2);
                    rr = lf - ce;
                    lr = rf - ce;
                    dst[0] = (lf & 0xFF);
                    dst[1] = ((lf >> 8) & 0xFF);
                    dst[2] = (rf & 0xFF);
                    dst[3] = ((rf >> 8) & 0xFF);

                    dst[0 + 4] = (lr & 0xFF);
                    dst[1 + 4] = ((lr >> 8) & 0xFF);
                    dst[2 + 4] = (rr & 0xFF);
                    dst[3 + 4] = ((rr >> 8) & 0xFF);
                }
            }
        }
        break;

    case AUDIO_S32:
        {
            const Uint32 *src = (const Uint32 *) (cvt->buf + cvt->len_cvt);
            Uint32 *dst = (Uint32 *) (cvt->buf + cvt->len_cvt * 2);
            Sint32 lf, rf, ce;

            if (SDL_AUDIO_ISBIGENDIAN(format)) {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 4;
                    src -= 2;
                    lf = (Sint32) SDL_SwapBE32(src[0]);
                    rf = (Sint32) SDL_SwapBE32(src[1]);
                    ce = (lf / 2) + (rf / 2);
                    dst[0] = src[0];
                    dst[1] = src[1];
                    dst[2] = SDL_SwapBE32((Uint32) (lf - ce));
                    dst[3] = SDL_SwapBE32((Uint32) (rf - ce));
                }
            } else {
                for (i = cvt->len_cvt / 8; i; --i) {
                    dst -= 4;
                    src -= 2;
                    lf = (Sint32) SDL_SwapLE32(src[0]);
                    rf = (Sint32) SDL_SwapLE32(src[1]);
                    ce = (lf / 2) + (rf / 2);
                    dst[0] = src[0];
                    dst[1] = src[1];
                    dst[2] = SDL_SwapLE32((Uint32) (lf - ce));
                    dst[3] = SDL_SwapLE32((Uint32) (rf - ce));
                }
            }
        }
        break;
    }
    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Convert rate up by multiple of 2 */
static void SDLCALL
SDL_RateMUL2(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate * 2 (mono)\n");
#endif

#define mul2_mono(type) { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + (cvt->len_cvt * 2)); \
        for (i = cvt->len_cvt / sizeof (type); i; --i) { \
            src--; \
            dst[-1] = dst[-2] = src[0]; \
            dst -= 2; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        mul2_mono(Uint8);
        break;
    case 16:
        mul2_mono(Uint16);
        break;
    case 32:
        mul2_mono(Uint32);
        break;
    }

#undef mul2_mono

    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Convert rate up by multiple of 2, for stereo */
static void SDLCALL
SDL_RateMUL2_c2(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate * 2 (stereo)\n");
#endif

#define mul2_stereo(type) { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + (cvt->len_cvt * 2)); \
        for (i = cvt->len_cvt / (sizeof (type) * 2); i; --i) { \
            const type r = src[-1]; \
            const type l = src[-2]; \
            src -= 2; \
            dst[-1] = r; \
            dst[-2] = l; \
            dst[-3] = r; \
            dst[-4] = l; \
            dst -= 4; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        mul2_stereo(Uint8);
        break;
    case 16:
        mul2_stereo(Uint16);
        break;
    case 32:
        mul2_stereo(Uint32);
        break;
    }

#undef mul2_stereo

    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Convert rate up by multiple of 2, for quad */
static void SDLCALL
SDL_RateMUL2_c4(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate * 2 (quad)\n");
#endif

#define mul2_quad(type) { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + (cvt->len_cvt * 2)); \
        for (i = cvt->len_cvt / (sizeof (type) * 4); i; --i) { \
            const type c1 = src[-1]; \
            const type c2 = src[-2]; \
            const type c3 = src[-3]; \
            const type c4 = src[-4]; \
            src -= 4; \
            dst[-1] = c1; \
            dst[-2] = c2; \
            dst[-3] = c3; \
            dst[-4] = c4; \
            dst[-5] = c1; \
            dst[-6] = c2; \
            dst[-7] = c3; \
            dst[-8] = c4; \
            dst -= 8; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        mul2_quad(Uint8);
        break;
    case 16:
        mul2_quad(Uint16);
        break;
    case 32:
        mul2_quad(Uint32);
        break;
    }

#undef mul2_quad

    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Convert rate up by multiple of 2, for 5.1 */
static void SDLCALL
SDL_RateMUL2_c6(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate * 2 (six channels)\n");
#endif

#define mul2_chansix(type) { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + (cvt->len_cvt * 2)); \
        for (i = cvt->len_cvt / (sizeof (type) * 6); i; --i) { \
            const type c1 = src[-1]; \
            const type c2 = src[-2]; \
            const type c3 = src[-3]; \
            const type c4 = src[-4]; \
            const type c5 = src[-5]; \
            const type c6 = src[-6]; \
            src -= 6; \
            dst[-1] = c1; \
            dst[-2] = c2; \
            dst[-3] = c3; \
            dst[-4] = c4; \
            dst[-5] = c5; \
            dst[-6] = c6; \
            dst[-7] = c1; \
            dst[-8] = c2; \
            dst[-9] = c3; \
            dst[-10] = c4; \
            dst[-11] = c5; \
            dst[-12] = c6; \
            dst -= 12; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        mul2_chansix(Uint8);
        break;
    case 16:
        mul2_chansix(Uint16);
        break;
    case 32:
        mul2_chansix(Uint32);
        break;
    }

#undef mul2_chansix

    cvt->len_cvt *= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Convert rate down by multiple of 2 */
static void SDLCALL
SDL_RateDIV2(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate / 2 (mono)\n");
#endif

#define div2_mono(type) { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 2); i; --i) { \
            dst[0] = src[0]; \
            src += 2; \
            dst++; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        div2_mono(Uint8);
        break;
    case 16:
        div2_mono(Uint16);
        break;
    case 32:
        div2_mono(Uint32);
        break;
    }

#undef div2_mono

    cvt->len_cvt /= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Convert rate down by multiple of 2, for stereo */
static void SDLCALL
SDL_RateDIV2_c2(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate / 2 (stereo)\n");
#endif

#define div2_stereo(type) { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 4); i; --i) { \
            dst[0] = src[0]; \
            dst[1] = src[1]; \
            src += 4; \
            dst += 2; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        div2_stereo(Uint8);
        break;
    case 16:
        div2_stereo(Uint16);
        break;
    case 32:
        div2_stereo(Uint32);
        break;
    }

#undef div2_stereo

    cvt->len_cvt /= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Convert rate down by multiple of 2, for quad */
static void SDLCALL
SDL_RateDIV2_c4(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate / 2 (quad)\n");
#endif

#define div2_quad(type) { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 8); i; --i) { \
            dst[0] = src[0]; \
            dst[1] = src[1]; \
            dst[2] = src[2]; \
            dst[3] = src[3]; \
            src += 8; \
            dst += 4; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        div2_quad(Uint8);
        break;
    case 16:
        div2_quad(Uint16);
        break;
    case 32:
        div2_quad(Uint32);
        break;
    }

#undef div2_quad

    cvt->len_cvt /= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Convert rate down by multiple of 2, for 5.1 */
static void SDLCALL
SDL_RateDIV2_c6(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate / 2 (six channels)\n");
#endif

#define div2_chansix(type) { \
        const type *src = (const type *) cvt->buf; \
        type *dst = (type *) cvt->buf; \
        for (i = cvt->len_cvt / (sizeof (type) * 12); i; --i) { \
            dst[0] = src[0]; \
            dst[1] = src[1]; \
            dst[2] = src[2]; \
            dst[3] = src[3]; \
            dst[4] = src[4]; \
            dst[5] = src[5]; \
            src += 12; \
            dst += 6; \
        } \
    }

    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        div2_chansix(Uint8);
        break;
    case 16:
        div2_chansix(Uint16);
        break;
    case 32:
        div2_chansix(Uint32);
        break;
    }

#undef div_chansix

    cvt->len_cvt /= 2;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

/* Very slow rate conversion routine */
static void SDLCALL
SDL_RateSLOW(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    double ipos;
    int i, clen;

#ifdef DEBUG_CONVERT
    fprintf(stderr, "Converting audio rate * %4.4f\n", 1.0 / cvt->rate_incr);
#endif
    clen = (int) ((double) cvt->len_cvt / cvt->rate_incr);
    if (cvt->rate_incr > 1.0) {
        switch (SDL_AUDIO_BITSIZE(format)) {
        case 8:
            {
                Uint8 *output;

                output = cvt->buf;
                ipos = 0.0;
                for (i = clen; i; --i) {
                    *output = cvt->buf[(int) ipos];
                    ipos += cvt->rate_incr;
                    output += 1;
                }
            }
            break;

        case 16:
            {
                Uint16 *output;

                clen &= ~1;
                output = (Uint16 *) cvt->buf;
                ipos = 0.0;
                for (i = clen / 2; i; --i) {
                    *output = ((Uint16 *) cvt->buf)[(int) ipos];
                    ipos += cvt->rate_incr;
                    output += 1;
                }
            }
            break;

        case 32:
            {
                /* !!! FIXME: need 32-bit converter here! */
#ifdef DEBUG_CONVERT
                fprintf(stderr, "FIXME: need 32-bit converter here!\n");
#endif
            }
        }
    } else {
        switch (SDL_AUDIO_BITSIZE(format)) {
        case 8:
            {
                Uint8 *output;

                output = cvt->buf + clen;
                ipos = (double) cvt->len_cvt;
                for (i = clen; i; --i) {
                    ipos -= cvt->rate_incr;
                    output -= 1;
                    *output = cvt->buf[(int) ipos];
                }
            }
            break;

        case 16:
            {
                Uint16 *output;

                clen &= ~1;
                output = (Uint16 *) (cvt->buf + clen);
                ipos = (double) cvt->len_cvt / 2;
                for (i = clen / 2; i; --i) {
                    ipos -= cvt->rate_incr;
                    output -= 1;
                    *output = ((Uint16 *) cvt->buf)[(int) ipos];
                }
            }
            break;

        case 32:
            {
                /* !!! FIXME: need 32-bit converter here! */
#ifdef DEBUG_CONVERT
                fprintf(stderr, "FIXME: need 32-bit converter here!\n");
#endif
            }
        }
    }

    cvt->len_cvt = clen;
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}

int
SDL_ConvertAudio(SDL_AudioCVT * cvt)
{
    /* Make sure there's data to convert */
    if (cvt->buf == NULL) {
        SDL_SetError("No buffer allocated for conversion");
        return (-1);
    }
    /* Return okay if no conversion is necessary */
    cvt->len_cvt = cvt->len;
    if (cvt->filters[0] == NULL) {
        return (0);
    }

    /* Set up the conversion and go! */
    cvt->filter_index = 0;
    cvt->filters[0] (cvt, cvt->src_format);
    return (0);
}


static SDL_AudioFilter
SDL_HandTunedTypeCVT(SDL_AudioFormat src_fmt, SDL_AudioFormat dst_fmt)
{
    /*
     * Fill in any future conversions that are specialized to a
     *  processor, platform, compiler, or library here.
     */

    return NULL;                /* no specialized converter code available. */
}


/*
 * Find a converter between two data types. We try to select a hand-tuned
 *  asm/vectorized/optimized function first, and then fallback to an
 *  autogenerated function that is customized to convert between two
 *  specific data types.
 */
static int
SDL_BuildAudioTypeCVT(SDL_AudioCVT * cvt,
                      SDL_AudioFormat src_fmt, SDL_AudioFormat dst_fmt)
{
    if (src_fmt != dst_fmt) {
        const Uint16 src_bitsize = SDL_AUDIO_BITSIZE(src_fmt);
        const Uint16 dst_bitsize = SDL_AUDIO_BITSIZE(dst_fmt);
        SDL_AudioFilter filter = SDL_HandTunedTypeCVT(src_fmt, dst_fmt);

        /* No hand-tuned converter? Try the autogenerated ones. */
        if (filter == NULL) {
            int i;
            for (i = 0; sdl_audio_type_filters[i].filter != NULL; i++) {
                const SDL_AudioTypeFilters *filt = &sdl_audio_type_filters[i];
                if ((filt->src_fmt == src_fmt) && (filt->dst_fmt == dst_fmt)) {
                    filter = filt->filter;
                    break;
                }
            }

            if (filter == NULL) {
                return -1;      /* Still no matching converter?! */
            }
        }

        /* Update (cvt) with filter details... */
        cvt->filters[cvt->filter_index++] = filter;
        if (src_bitsize < dst_bitsize) {
            const int mult = (dst_bitsize / src_bitsize);
            cvt->len_mult *= mult;
            cvt->len_ratio *= mult;
        } else if (src_bitsize > dst_bitsize) {
            cvt->len_ratio /= (src_bitsize / dst_bitsize);
        }

        return 1;               /* added a converter. */
    }

    return 0;                   /* no conversion necessary. */
}

/* Generate the necessary IIR lowpass coefficients for resampling.
   Assume that the SDL_AudioCVT struct is already set up with
   the correct values for len_mult and len_div, and use the
   type of dst_format. Also assume the buffer is allocated.
   Note the buffer needs to be 6 units long.
   For now, use RBJ's cookbook coefficients. It might be more
   optimal to create a Butterworth filter, but this is more difficult.
*/
int SDL_BuildIIRLowpass(SDL_AudioCVT * cvt, SDL_AudioFormat format) {
	float fc;			/* cutoff frequency */
	float coeff[6];		/* floating point iir coefficients b0, b1, b2, a0, a1, a2 */
	float scale;
	float w0, alpha, cosw0;
	int i;
	
	/* The higher Q is, the higher CUTOFF can be. Need to find a good balance to avoid aliasing */
	static const float Q = 5.0f;
	static const float CUTOFF = 0.4f;
	
	fc = (cvt->len_mult > cvt->len_div) ? CUTOFF / (float)cvt->len_mult : CUTOFF / (float)cvt->len_div;
	
	w0 = 2.0f * M_PI * fc;
	cosw0 = cosf(w0);
	alpha = sin(w0) / (2.0f * Q);
	
	/* Compute coefficients, normalizing by a0 */
	scale = 1.0f / (1.0f + alpha);
	
	coeff[0] = (1.0f - cosw0) / 2.0f * scale;
	coeff[1] = (1.0f - cosw0) * scale;
	coeff[2] = coeff[0];
	
	coeff[3] = 1.0f;	/* a0 is normalized to 1 */
	coeff[4] = -2.0f * cosw0 * scale;
	coeff[5] = (1.0f - alpha) * scale;
	
	/* Copy the coefficients to the struct. If necessary, convert coefficients to fixed point, using the range (-2.0, 2.0) */
#define convert_fixed(type, fix) { \
			type *cvt_coeff = (type *)cvt->coeff; \
			for(i = 0; i < 6; ++i) { \
				cvt_coeff[i] = fix(coeff[i]); \
			} \
		}
		
	if(SDL_AUDIO_ISFLOAT(format) && SDL_AUDIO_BITSIZE(format) == 32) {
		float *cvt_coeff = (float *)cvt->coeff;
		for(i = 0; i < 6; ++i) {
			cvt_coeff[i] = coeff[i];
		}
	} else {
		switch(SDL_AUDIO_BITSIZE(format)) {
			case 8:
				convert_fixed(Uint8, SDL_Make_2_6);
				break;
			case 16:
				convert_fixed(Uint16, SDL_Make_2_14);
				break;
			case 32:
				convert_fixed(Uint32, SDL_Make_2_30);
				break;
		}
	}
	
#ifdef DEBUG_CONVERT
#define debug_iir(type) { \
			type *cvt_coeff = (type *)cvt->coeff; \
			for(i = 0; i < 6; ++i) { \
				printf("coeff[%u] = %f = 0x%x\n", i, coeff[i], cvt_coeff[i]); \
			} \
		}
		if(SDL_AUDIO_ISFLOAT(format) && SDL_AUDIO_BITSIZE(format) == 32) {
			float *cvt_coeff = (float *)cvt->coeff;
			for(i = 0; i < 6; ++i) { \
				printf("coeff[%u] = %f = %f\n", i, coeff[i], cvt_coeff[i]); \
			}
		} else {
			switch(SDL_AUDIO_BITSIZE(format)) {
				case 8:
					debug_iir(Uint8);
					break;
				case 16:
					debug_iir(Uint16);
					break;
				case 32:
					debug_iir(Uint32);
					break;
			}
		}
#undef debug_iir
#endif
	
	/* Initialize the state buffer to all zeroes, and set initial position */
	memset(cvt->state_buf, 0, 4 * SDL_AUDIO_BITSIZE(format) / 4);
	cvt->state_pos = 0;
#undef convert_fixed
}

/* Apply the lowpass IIR filter to the given SDL_AudioCVT struct */
static void SDL_FilterIIR(SDL_AudioCVT * cvt, SDL_AudioFormat format) {
	Uint32 i, n;
	
	/* TODO: Check that n is calculated right */
	n = 8 * cvt->len_cvt / SDL_AUDIO_BITSIZE(format);

	/* Note that the coefficients are 2_x and the input is 1_x. Do we need to shift left at the end here? The right shift temp = buf[n] >> 1 needs to depend on whether the type is signed or not for sign extension.*/
	/* cvt->state_pos = 1: state[0] = x_n-1, state[1] = x_n-2, state[2] = y_n-1, state[3] - y_n-2 */
#define iir_fix(type, mult) {\
			type *coeff = (type *)cvt->coeff; \
			type *state = (type *)cvt->state_buf; \
			type *buf = (type *)cvt->buf; \
			type temp; \
			for(i = 0; i < n; ++i) { \
					temp = buf[i] >> 1; \
					if(cvt->state_pos) { \
						buf[i] = mult(coeff[0], temp) + mult(coeff[1], state[0]) + mult(coeff[2], state[1]) - mult(coeff[4], state[2]) - mult(coeff[5], state[3]); \
						state[1] = temp; \
						state[3] = buf[i]; \
						cvt->state_pos = 0; \
					} else { \
						buf[i] = mult(coeff[0], temp) + mult(coeff[1], state[1]) + mult(coeff[2], state[0]) - mult(coeff[4], state[3]) - mult(coeff[5], state[2]); \
						state[0] = temp; \
						state[2] = buf[i]; \
						cvt->state_pos = 1; \
					} \
				} \
		}
/* Need to test to see if the previous method or this one is faster */
/*#define iir_fix(type, mult) {\
			type *coeff = (type *)cvt->coeff; \
			type *state = (type *)cvt->state_buf; \
			type *buf = (type *)cvt->buf; \
			type temp; \
			for(i = 0; i < n; ++i) { \
					temp = buf[i] >> 1; \
					buf[i] = mult(coeff[0], temp) + mult(coeff[1], state[0]) + mult(coeff[2], state[1]) - mult(coeff[4], state[2]) - mult(coeff[5], state[3]); \
					state[1] = state[0]; \
					state[0] = temp; \
					state[3] = state[2]; \
					state[2] = buf[i]; \
				} \
		}*/

	if(SDL_AUDIO_ISFLOAT(format) && SDL_AUDIO_BITSIZE(format) == 32) {
		float *coeff = (float *)cvt->coeff;
		float *state = (float *)cvt->state_buf;
		float *buf = (float *)cvt->buf;
		float temp;

		for(i = 0; i < n; ++i) {
			/* y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a[2] * y[n-2] */
			temp = buf[i];
			if(cvt->state_pos) {
				buf[i] = coeff[0] * buf[n] + coeff[1] * state[0] + coeff[2] * state[1] - coeff[4] * state[2] - coeff[5] * state[3];
				state[1] = temp;
				state[3] = buf[i];
				cvt->state_pos = 0;
			} else {
				buf[i] = coeff[0] * buf[n] + coeff[1] * state[1] + coeff[2] * state[0] - coeff[4] * state[3] - coeff[5] * state[2];
				state[0] = temp;
				state[2] = buf[i];
				cvt->state_pos = 1;
			}
		}
	} else {
		/* Treat everything as signed! */
		switch(SDL_AUDIO_BITSIZE(format)) {
			case 8:
				iir_fix(Sint8, SDL_FixMpy8);
				break;
			case 16:
				iir_fix(Sint16, SDL_FixMpy16);
				break;
			case 32:
				iir_fix(Sint32, SDL_FixMpy32);
				break;
		}
	}
#undef iir_fix
}

/* Apply the windowed sinc FIR filter to the given SDL_AudioCVT struct */
static void SDL_FilterFIR(SDL_AudioCVT * cvt, SDL_AudioFormat format) {
	int n = 8 * cvt->len_cvt / SDL_AUDIO_BITSIZE(format);
	int m = cvt->len_sinc;
	int i, j;
				
	/* 
	   Note: We can make a big optimization here by taking advantage
	   of the fact that the signal is zero stuffed, so we can do
	   significantly fewer multiplications and additions. However, this
	   depends on the zero stuffing ratio, so it may not pay off.
	*/
#define filter_sinc(type, mult) { \
			type *sinc = (type *)cvt->coeff; \
			type *state = (type *)cvt->state_buf; \
			type *buf = (type *)cvt->buf; \
			for(i = 0; i < n; ++i) { \
				state[cvt->state_pos] = buf[i]; \
				buf[i] = 0; \
				for(j = 0; j < m;  ++j) { \
					buf[i] += mult(sinc[j], state[(cvt->state_pos + j) % m]); \
				} \
				cvt->state_pos = (cvt->state_pos + 1) % m; \
			} \
		}
	
	/* If it's floating point, do it normally, otherwise used fixed-point code */
	if(SDL_AUDIO_ISFLOAT(format) && SDL_AUDIO_BITSIZE(format) == 32) {
		float *sinc = (float *)cvt->coeff;
		float *state = (float *)cvt->state_buf;
		float *buf = (float *)cvt->buf;
		
		for(i = 0; i < n; ++i) {
			state[cvt->state_pos] = buf[i];
			buf[i] = 0.0f;
			for(j = 0; j < m; ++j) {
				buf[i] += sinc[j] * state[(cvt->state_pos + j) % m];
			}
			cvt->state_pos = (cvt->state_pos + 1) % m;
		}
	} else {
		switch (SDL_AUDIO_BITSIZE(format)) {
			case 8:
				filter_sinc(Sint8, SDL_FixMpy8);
				break;
			case 16:
				filter_sinc(Sint16, SDL_FixMpy16);
				break;
			case 32:
				filter_sinc(Sint32, SDL_FixMpy32);
				break;
		}
	}
	
#undef filter_sinc
			
}

/* Generate the necessary windowed sinc filter for resampling.
   Assume that the SDL_AudioCVT struct is already set up with
   the correct values for len_mult and len_div, and use the
   type of dst_format. Also assume the buffer is allocated.
   Note the buffer needs to be m+1 units long.
*/
int
SDL_BuildWindowedSinc(SDL_AudioCVT * cvt, SDL_AudioFormat format, unsigned int m) {
	float fScale;		/* scale factor for fixed point */
	float *fSinc;		/* floating point sinc buffer, to be converted to fixed point */
	float fc;			/* cutoff frequency */
	float two_pi_fc, two_pi_over_m, four_pi_over_m, m_over_two;
	float norm_sum, norm_fact;
	unsigned int i;

	/* Check that the buffer is allocated */
	if( cvt->coeff == NULL ) {
		return -1;
	}

	/* Set the length */
	cvt->len_sinc = m + 1;
	
	/* Allocate the floating point windowed sinc. */
	fSinc = (float *)malloc(m * sizeof(float));
	if( fSinc == NULL ) {
		return -1;
	}
	
	/* Set up the filter parameters */
	fc = (cvt->len_mult > cvt->len_div) ? 0.5f / (float)cvt->len_mult : 0.5f / (float)cvt->len_div;
#ifdef DEBUG_CONVERT
	printf("Lowpass cutoff frequency = %f\n", fc);
#endif
//	fc = 0.02f;
	two_pi_fc = 2.0f * M_PI * fc;
	two_pi_over_m = 2.0f * M_PI / (float)m;
	four_pi_over_m = 2.0f * two_pi_over_m;
	m_over_two = (float)m / 2.0f;
	norm_sum = 0.0f;
	
	for(i = 0; i <= m; ++i ) {
		if( i == m/2 ) {
			fSinc[i] = two_pi_fc;
		} else {
			fSinc[i] = sinf(two_pi_fc * ((float)i - m_over_two)) / ((float)i - m_over_two);
			/* Apply blackman window */
			fSinc[i] *= 0.42f - 0.5f * cosf(two_pi_over_m * (float)i) + 0.08f * cosf(four_pi_over_m * (float)i);
		}
		norm_sum += fabs(fSinc[i]);
	}
		
#define convert_fixed(type, fix) { \
		norm_fact = 0.7f / norm_sum; \
		type *dst = (type *)cvt->coeff; \
		for( i = 0; i <= m; ++i ) { \
			dst[i] = fix(fSinc[i] * norm_fact); \
		} \
	}
	
	/* If we're using floating point, we only need to normalize */
	if(SDL_AUDIO_ISFLOAT(format) && SDL_AUDIO_BITSIZE(format) == 32) {
		float *fDest = (float *)cvt->coeff;
		norm_fact = 1.0f / norm_sum;
		for(i = 0; i <= m; ++i) {
			fDest[i] = fSinc[i] * norm_fact;
		}
	} else {
		switch (SDL_AUDIO_BITSIZE(format)) {
			case 8:
				convert_fixed(Uint8, SDL_Make_1_7);
				break;
			case 16:
				convert_fixed(Uint16, SDL_Make_1_15);
				break;
			case 32:
				convert_fixed(Uint32, SDL_Make_1_31);
				break;
		}
	}
	
	/* Initialize the state buffer to all zeroes, and set initial position */
	memset(cvt->state_buf, 0, cvt->len_sinc * SDL_AUDIO_BITSIZE(format) / 4);
	cvt->state_pos = 0;
	
	/* Clean up */
#undef convert_fixed
	free(fSinc);
}

/* This is used to reduce the resampling ratio */
inline int SDL_GCD(int a, int b) {
	int temp;
	while(b != 0) {
		temp = a % b;
		a = b;
		b = temp;
	}
	return a;
}

/* Perform proper resampling */
static void SDLCALL
SDL_Resample(SDL_AudioCVT * cvt, SDL_AudioFormat format)
{
    int i, j;

#ifdef DEBUG_CONVERT
    printf("Converting audio rate via proper resampling (mono)\n");
#endif

#define zerostuff_mono(type) { \
        const type *src = (const type *) (cvt->buf + cvt->len_cvt); \
        type *dst = (type *) (cvt->buf + (cvt->len_cvt * cvt->len_mult)); \
        for (i = cvt->len_cvt / sizeof (type); i; --i) { \
            src--; \
            dst[-1] = src[0]; \
			for( j = -cvt->len_mult; j < -1; ++j ) { \
				dst[j] = 0; \
			} \
            dst -= cvt->len_mult; \
        } \
    }
	
#define discard_mono(type) { \
        const type *src = (const type *) (cvt->buf); \
        type *dst = (type *) (cvt->buf); \
        for (i = 0; i < cvt->len_cvt / cvt->len_div / sizeof (type); ++i) { \
            dst[0] = src[0]; \
            src += cvt->len_div; \
            ++dst; \
        } \
    }

	// Step 1: Zero stuff the conversion buffer
#ifdef DEBUG_CONVERT
	printf("Zero-stuffing by a factor of %u\n", cvt->len_mult);
#endif
    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        zerostuff_mono(Uint8);
        break;
    case 16:
        zerostuff_mono(Uint16);
        break;
    case 32:
        zerostuff_mono(Uint32);
        break;
    }
	
	cvt->len_cvt *= cvt->len_mult;

	// Step 2: Use either a windowed sinc FIR filter or IIR lowpass filter to remove all alias frequencies
	SDL_FilterFIR( cvt, format );
	
	// Step 3: Discard unnecessary samples
#ifdef DEBUG_CONVERT
	printf("Discarding samples by a factor of %u\n", cvt->len_div);
#endif
    switch (SDL_AUDIO_BITSIZE(format)) {
    case 8:
        discard_mono(Uint8);
        break;
    case 16:
        discard_mono(Uint16);
        break;
    case 32:
        discard_mono(Uint32);
        break;
    }
	
#undef zerostuff_mono
#undef discard_mono

    cvt->len_cvt /= cvt->len_div;
	
    if (cvt->filters[++cvt->filter_index]) {
        cvt->filters[cvt->filter_index] (cvt, format);
    }
}


/* Creates a set of audio filters to convert from one format to another.
   Returns -1 if the format conversion is not supported, 0 if there's
   no conversion needed, or 1 if the audio filter is set up.
*/

int
SDL_BuildAudioCVT(SDL_AudioCVT * cvt,
                  SDL_AudioFormat src_fmt, Uint8 src_channels, int src_rate,
                  SDL_AudioFormat dst_fmt, Uint8 dst_channels, int dst_rate)
{
    /* there are no unsigned types over 16 bits, so catch this upfront. */
    if ((SDL_AUDIO_BITSIZE(src_fmt) > 16) && (!SDL_AUDIO_ISSIGNED(src_fmt))) {
        return -1;
    }
    if ((SDL_AUDIO_BITSIZE(dst_fmt) > 16) && (!SDL_AUDIO_ISSIGNED(dst_fmt))) {
        return -1;
    }
#ifdef DEBUG_CONVERT
    printf("Build format %04x->%04x, channels %u->%u, rate %d->%d\n",
           src_fmt, dst_fmt, src_channels, dst_channels, src_rate, dst_rate);
#endif

    /* Start off with no conversion necessary */

    cvt->src_format = src_fmt;
    cvt->dst_format = dst_fmt;
    cvt->needed = 0;
    cvt->filter_index = 0;
    cvt->filters[0] = NULL;
    cvt->len_mult = 1;
    cvt->len_ratio = 1.0;

    /* Convert data types, if necessary. Updates (cvt). */
    if (SDL_BuildAudioTypeCVT(cvt, src_fmt, dst_fmt) == -1)
        return -1;              /* shouldn't happen, but just in case... */

    /* Channel conversion */
    if (src_channels != dst_channels) {
        if ((src_channels == 1) && (dst_channels > 1)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertStereo;
            cvt->len_mult *= 2;
            src_channels = 2;
            cvt->len_ratio *= 2;
        }
        if ((src_channels == 2) && (dst_channels == 6)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertSurround;
            src_channels = 6;
            cvt->len_mult *= 3;
            cvt->len_ratio *= 3;
        }
        if ((src_channels == 2) && (dst_channels == 4)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertSurround_4;
            src_channels = 4;
            cvt->len_mult *= 2;
            cvt->len_ratio *= 2;
        }
        while ((src_channels * 2) <= dst_channels) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertStereo;
            cvt->len_mult *= 2;
            src_channels *= 2;
            cvt->len_ratio *= 2;
        }
        if ((src_channels == 6) && (dst_channels <= 2)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertStrip;
            src_channels = 2;
            cvt->len_ratio /= 3;
        }
        if ((src_channels == 6) && (dst_channels == 4)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertStrip_2;
            src_channels = 4;
            cvt->len_ratio /= 2;
        }
        /* This assumes that 4 channel audio is in the format:
           Left {front/back} + Right {front/back}
           so converting to L/R stereo works properly.
         */
        while (((src_channels % 2) == 0) &&
               ((src_channels / 2) >= dst_channels)) {
            cvt->filters[cvt->filter_index++] = SDL_ConvertMono;
            src_channels /= 2;
            cvt->len_ratio /= 2;
        }
        if (src_channels != dst_channels) {
            /* Uh oh.. */ ;
        }
    }

    /* Do rate conversion */
	int rate_gcd;
	rate_gcd = SDL_GCD(src_rate, dst_rate);
	cvt->len_mult = dst_rate / rate_gcd;
	cvt->len_div = src_rate / rate_gcd;
	cvt->len_ratio = (double)cvt->len_mult / (double)cvt->len_div;
	cvt->filters[cvt->filter_index++] = SDL_Resample;
	//SDL_BuildIIRLowpass(cvt, dst_fmt);
	SDL_BuildWindowedSinc(cvt, dst_fmt, 20);
	
    /*cvt->rate_incr = 0.0;
    if ((src_rate / 100) != (dst_rate / 100)) {
        Uint32 hi_rate, lo_rate;
        int len_mult;
        double len_ratio;
        SDL_AudioFilter rate_cvt = NULL;

        if (src_rate > dst_rate) {
            hi_rate = src_rate;
            lo_rate = dst_rate;
            switch (src_channels) {
            case 1:
                rate_cvt = SDL_RateDIV2;
                break;
            case 2:
                rate_cvt = SDL_RateDIV2_c2;
                break;
            case 4:
                rate_cvt = SDL_RateDIV2_c4;
                break;
            case 6:
                rate_cvt = SDL_RateDIV2_c6;
                break;
            default:
                return -1;
            }
            len_mult = 1;
            len_ratio = 0.5;
        } else {
            hi_rate = dst_rate;
            lo_rate = src_rate;
            switch (src_channels) {
            case 1:
                rate_cvt = SDL_RateMUL2;
                break;
            case 2:
                rate_cvt = SDL_RateMUL2_c2;
                break;
            case 4:
                rate_cvt = SDL_RateMUL2_c4;
                break;
            case 6:
                rate_cvt = SDL_RateMUL2_c6;
                break;
            default:
                return -1;
            }
            len_mult = 2;
            len_ratio = 2.0;
        }*/
        /* If hi_rate = lo_rate*2^x then conversion is easy */
        /*while (((lo_rate * 2) / 100) <= (hi_rate / 100)) {
            cvt->filters[cvt->filter_index++] = rate_cvt;
            cvt->len_mult *= len_mult;
            lo_rate *= 2;
            cvt->len_ratio *= len_ratio;
        }*/
        /* We may need a slow conversion here to finish up */
        /*if ((lo_rate / 100) != (hi_rate / 100)) {*/
#if 1
            /* The problem with this is that if the input buffer is
               say 1K, and the conversion rate is say 1.1, then the
               output buffer is 1.1K, which may not be an acceptable
               buffer size for the audio driver (not a power of 2)
             */
            /* For now, punt and hope the rate distortion isn't great.
             */
#else
            if (src_rate < dst_rate) {
                cvt->rate_incr = (double) lo_rate / hi_rate;
                cvt->len_mult *= 2;
                cvt->len_ratio /= cvt->rate_incr;
            } else {
                cvt->rate_incr = (double) hi_rate / lo_rate;
                cvt->len_ratio *= cvt->rate_incr;
            }
            cvt->filters[cvt->filter_index++] = SDL_RateSLOW;
#endif
/*        }
    }*/

    /* Set up the filter information */
    if (cvt->filter_index != 0) {
        cvt->needed = 1;
        cvt->src_format = src_fmt;
        cvt->dst_format = dst_fmt;
        cvt->len = 0;
        cvt->buf = NULL;
        cvt->filters[cvt->filter_index] = NULL;
    }
    return (cvt->needed);
}

#undef SDL_FixMpy8
#undef SDL_FixMpy16
#undef SDL_FixMpy32
#undef SDL_Make_1_7
#undef SDL_Make_1_15
#undef SDL_Make_1_31
#undef SDL_Make_2_6
#undef SDL_Make_2_14
#undef SDL_Make_2_30

/* vi: set ts=4 sw=4 expandtab: */