src/libm/k_rem_pio2.c
author Ryan C. Gordon <icculus@icculus.org>
Fri, 12 Aug 2016 19:59:00 -0400
changeset 10266 c09f06c4e8c8
parent 8670 0c15c8a2f8c3
permissions -rw-r--r--
emscripten: send fake mouse events for touches, like other targets do. (This really should be handled at the higher level and not in the individual targets, but this fixes the immediate bug.)

/* @(#)k_rem_pio2.c 5.1 93/09/24 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#if defined(LIBM_SCCS) && !defined(lint)
static const char rcsid[] =
    "$NetBSD: k_rem_pio2.c,v 1.7 1995/05/10 20:46:25 jtc Exp $";
#endif

/*
 * __kernel_rem_pio2(x,y,e0,nx,prec,ipio2)
 * double x[],y[]; int e0,nx,prec; int ipio2[];
 *
 * __kernel_rem_pio2 return the last three digits of N with
 *		y = x - N*pi/2
 * so that |y| < pi/2.
 *
 * The method is to compute the integer (mod 8) and fraction parts of
 * (2/pi)*x without doing the full multiplication. In general we
 * skip the part of the product that are known to be a huge integer (
 * more accurately, = 0 mod 8 ). Thus the number of operations are
 * independent of the exponent of the input.
 *
 * (2/pi) is represented by an array of 24-bit integers in ipio2[].
 *
 * Input parameters:
 * 	x[]	The input value (must be positive) is broken into nx
 *		pieces of 24-bit integers in double precision format.
 *		x[i] will be the i-th 24 bit of x. The scaled exponent
 *		of x[0] is given in input parameter e0 (i.e., x[0]*2^e0
 *		match x's up to 24 bits.
 *
 *		Example of breaking a double positive z into x[0]+x[1]+x[2]:
 *			e0 = ilogb(z)-23
 *			z  = scalbn(z,-e0)
 *		for i = 0,1,2
 *			x[i] = floor(z)
 *			z    = (z-x[i])*2**24
 *
 *
 *	y[]	ouput result in an array of double precision numbers.
 *		The dimension of y[] is:
 *			24-bit  precision	1
 *			53-bit  precision	2
 *			64-bit  precision	2
 *			113-bit precision	3
 *		The actual value is the sum of them. Thus for 113-bit
 *		precison, one may have to do something like:
 *
 *		long double t,w,r_head, r_tail;
 *		t = (long double)y[2] + (long double)y[1];
 *		w = (long double)y[0];
 *		r_head = t+w;
 *		r_tail = w - (r_head - t);
 *
 *	e0	The exponent of x[0]
 *
 *	nx	dimension of x[]
 *
 *  	prec	an integer indicating the precision:
 *			0	24  bits (single)
 *			1	53  bits (double)
 *			2	64  bits (extended)
 *			3	113 bits (quad)
 *
 *	ipio2[]
 *		integer array, contains the (24*i)-th to (24*i+23)-th
 *		bit of 2/pi after binary point. The corresponding
 *		floating value is
 *
 *			ipio2[i] * 2^(-24(i+1)).
 *
 * External function:
 *	double scalbn(), floor();
 *
 *
 * Here is the description of some local variables:
 *
 * 	jk	jk+1 is the initial number of terms of ipio2[] needed
 *		in the computation. The recommended value is 2,3,4,
 *		6 for single, double, extended,and quad.
 *
 * 	jz	local integer variable indicating the number of
 *		terms of ipio2[] used.
 *
 *	jx	nx - 1
 *
 *	jv	index for pointing to the suitable ipio2[] for the
 *		computation. In general, we want
 *			( 2^e0*x[0] * ipio2[jv-1]*2^(-24jv) )/8
 *		is an integer. Thus
 *			e0-3-24*jv >= 0 or (e0-3)/24 >= jv
 *		Hence jv = max(0,(e0-3)/24).
 *
 *	jp	jp+1 is the number of terms in PIo2[] needed, jp = jk.
 *
 * 	q[]	double array with integral value, representing the
 *		24-bits chunk of the product of x and 2/pi.
 *
 *	q0	the corresponding exponent of q[0]. Note that the
 *		exponent for q[i] would be q0-24*i.
 *
 *	PIo2[]	double precision array, obtained by cutting pi/2
 *		into 24 bits chunks.
 *
 *	f[]	ipio2[] in floating point
 *
 *	iq[]	integer array by breaking up q[] in 24-bits chunk.
 *
 *	fq[]	final product of x*(2/pi) in fq[0],..,fq[jk]
 *
 *	ih	integer. If >0 it indicates q[] is >= 0.5, hence
 *		it also indicates the *sign* of the result.
 *
 */


/*
 * Constants:
 * The hexadecimal values are the intended ones for the following
 * constants. The decimal values may be used, provided that the
 * compiler will convert from decimal to binary accurately enough
 * to produce the hexadecimal values shown.
 */

#include "math_libm.h"
#include "math_private.h"

#include "SDL_assert.h"

libm_hidden_proto(scalbn)
    libm_hidden_proto(floor)
#ifdef __STDC__
     static const int init_jk[] = { 2, 3, 4, 6 };       /* initial value for jk */
#else
     static int init_jk[] = { 2, 3, 4, 6 };
#endif

#ifdef __STDC__
static const double PIo2[] = {
#else
static double PIo2[] = {
#endif
    1.57079625129699707031e+00, /* 0x3FF921FB, 0x40000000 */
    7.54978941586159635335e-08, /* 0x3E74442D, 0x00000000 */
    5.39030252995776476554e-15, /* 0x3CF84698, 0x80000000 */
    3.28200341580791294123e-22, /* 0x3B78CC51, 0x60000000 */
    1.27065575308067607349e-29, /* 0x39F01B83, 0x80000000 */
    1.22933308981111328932e-36, /* 0x387A2520, 0x40000000 */
    2.73370053816464559624e-44, /* 0x36E38222, 0x80000000 */
    2.16741683877804819444e-51, /* 0x3569F31D, 0x00000000 */
};

#ifdef __STDC__
static const double
#else
static double
#endif
  zero = 0.0, one = 1.0, two24 = 1.67772160000000000000e+07,    /* 0x41700000, 0x00000000 */
    twon24 = 5.96046447753906250000e-08;        /* 0x3E700000, 0x00000000 */

#ifdef __STDC__
int attribute_hidden
__kernel_rem_pio2(double *x, double *y, int e0, int nx, int prec,
                  const int32_t * ipio2)
#else
int attribute_hidden
__kernel_rem_pio2(x, y, e0, nx, prec, ipio2)
     double x[], y[];
     int e0, nx, prec;
     int32_t ipio2[];
#endif
{
    int32_t jz, jx, jv, jp, jk, carry, n, iq[20], i, j, k, m, q0, ih;
    double z, fw, f[20], fq[20], q[20];

    /* initialize jk */
    SDL_assert((prec >= 0) && (prec < SDL_arraysize(init_jk)));
    jk = init_jk[prec];
    SDL_assert((jk >= 2) && (jk <= 6));
    jp = jk;

    /* determine jx,jv,q0, note that 3>q0 */
    SDL_assert(nx > 0);
    jx = nx - 1;
    jv = (e0 - 3) / 24;
    if (jv < 0)
        jv = 0;
    q0 = e0 - 24 * (jv + 1);

    /* set up f[0] to f[jx+jk] where f[jx+jk] = ipio2[jv+jk] */
    j = jv - jx;
    m = jx + jk;
    for (i = 0; i <= m; i++, j++)
        f[i] = (j < 0) ? zero : (double) ipio2[j];

    /* compute q[0],q[1],...q[jk] */
    for (i = 0; i <= jk; i++) {
        for (j = 0, fw = 0.0; j <= jx; j++)
            fw += x[j] * f[jx + i - j];
        q[i] = fw;
    }

    jz = jk;
  recompute:
    /* distill q[] into iq[] reversingly */
    for (i = 0, j = jz, z = q[jz]; j > 0; i++, j--) {
        fw = (double) ((int32_t) (twon24 * z));
        iq[i] = (int32_t) (z - two24 * fw);
        z = q[j - 1] + fw;
    }

    /* compute n */
    z = scalbn(z, q0);          /* actual value of z */
    z -= 8.0 * floor(z * 0.125);        /* trim off integer >= 8 */
    n = (int32_t) z;
    z -= (double) n;
    ih = 0;
    if (q0 > 0) {               /* need iq[jz-1] to determine n */
        i = (iq[jz - 1] >> (24 - q0));
        n += i;
        iq[jz - 1] -= i << (24 - q0);
        ih = iq[jz - 1] >> (23 - q0);
    } else if (q0 == 0)
        ih = iq[jz - 1] >> 23;
    else if (z >= 0.5)
        ih = 2;

    if (ih > 0) {               /* q > 0.5 */
        n += 1;
        carry = 0;
        for (i = 0; i < jz; i++) {      /* compute 1-q */
            j = iq[i];
            if (carry == 0) {
                if (j != 0) {
                    carry = 1;
                    iq[i] = 0x1000000 - j;
                }
            } else
                iq[i] = 0xffffff - j;
        }
        if (q0 > 0) {           /* rare case: chance is 1 in 12 */
            switch (q0) {
            case 1:
                iq[jz - 1] &= 0x7fffff;
                break;
            case 2:
                iq[jz - 1] &= 0x3fffff;
                break;
            }
        }
        if (ih == 2) {
            z = one - z;
            if (carry != 0)
                z -= scalbn(one, q0);
        }
    }

    /* check if recomputation is needed */
    if (z == zero) {
        j = 0;
        for (i = jz - 1; i >= jk; i--)
            j |= iq[i];
        if (j == 0) {           /* need recomputation */
            for (k = 1; iq[jk - k] == 0; k++);  /* k = no. of terms needed */

            for (i = jz + 1; i <= jz + k; i++) {        /* add q[jz+1] to q[jz+k] */
                f[jx + i] = (double) ipio2[jv + i];
                for (j = 0, fw = 0.0; j <= jx; j++)
                    fw += x[j] * f[jx + i - j];
                q[i] = fw;
            }
            jz += k;
            goto recompute;
        }
    }

    /* chop off zero terms */
    if (z == 0.0) {
        jz -= 1;
        q0 -= 24;
        while (iq[jz] == 0) {
            jz--;
            q0 -= 24;
        }
    } else {                    /* break z into 24-bit if necessary */
        z = scalbn(z, -q0);
        if (z >= two24) {
            fw = (double) ((int32_t) (twon24 * z));
            iq[jz] = (int32_t) (z - two24 * fw);
            jz += 1;
            q0 += 24;
            iq[jz] = (int32_t) fw;
        } else
            iq[jz] = (int32_t) z;
    }

    /* convert integer "bit" chunk to floating-point value */
    fw = scalbn(one, q0);
    for (i = jz; i >= 0; i--) {
        q[i] = fw * (double) iq[i];
        fw *= twon24;
    }

    /* compute PIo2[0,...,jp]*q[jz,...,0] */
    for (i = jz; i >= 0; i--) {
        for (fw = 0.0, k = 0; k <= jp && k <= jz - i; k++)
            fw += PIo2[k] * q[i + k];
        fq[jz - i] = fw;
    }

    /* compress fq[] into y[] */
    switch (prec) {
    case 0:
        fw = 0.0;
        for (i = jz; i >= 0; i--)
            fw += fq[i];
        y[0] = (ih == 0) ? fw : -fw;
        break;
    case 1:
    case 2:
        fw = 0.0;
        for (i = jz; i >= 0; i--)
            fw += fq[i];
        y[0] = (ih == 0) ? fw : -fw;
        fw = fq[0] - fw;
        for (i = 1; i <= jz; i++)
            fw += fq[i];
        y[1] = (ih == 0) ? fw : -fw;
        break;
    case 3:                    /* painful */
        for (i = jz; i > 0; i--) {
            fw = fq[i - 1] + fq[i];
            fq[i] += fq[i - 1] - fw;
            fq[i - 1] = fw;
        }
        for (i = jz; i > 1; i--) {
            fw = fq[i - 1] + fq[i];
            fq[i] += fq[i - 1] - fw;
            fq[i - 1] = fw;
        }
        for (fw = 0.0, i = jz; i >= 2; i--)
            fw += fq[i];
        if (ih == 0) {
            y[0] = fq[0];
            y[1] = fq[1];
            y[2] = fw;
        } else {
            y[0] = -fq[0];
            y[1] = -fq[1];
            y[2] = -fw;
        }
    }
    return n & 7;
}