src/video/e_pow.h
author Sam Lantinga <slouken@libsdl.org>
Tue, 07 Feb 2006 18:36:54 +0000
changeset 1345 7f32b9bede06
parent 1330 450721ad5436
child 1424 7a610f25c12f
permissions -rw-r--r--
Fixes for Visual C++ 6.0
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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/* @(#)e_pow.c 5.1 93/09/24 */
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/*
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 * ====================================================
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 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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 *
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 * Developed at SunPro, a Sun Microsystems, Inc. business.
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 * Permission to use, copy, modify, and distribute this
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 * software is freely granted, provided that this notice
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 * is preserved.
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 * ====================================================
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 */
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#if defined(LIBM_SCCS) && !defined(lint)
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static char rcsid[] = "$NetBSD: e_pow.c,v 1.9 1995/05/12 04:57:32 jtc Exp $";
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#endif
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/* __ieee754_pow(x,y) return x**y
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 *
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 *		      n
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 * Method:  Let x =  2   * (1+f)
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 *	1. Compute and return log2(x) in two pieces:
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 *		log2(x) = w1 + w2,
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 *	   where w1 has 53-24 = 29 bit trailing zeros.
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 *	2. Perform y*log2(x) = n+y' by simulating muti-precision
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 *	   arithmetic, where |y'|<=0.5.
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 *	3. Return x**y = 2**n*exp(y'*log2)
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 *
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 * Special cases:
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 *	1.  (anything) ** 0  is 1
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 *	2.  (anything) ** 1  is itself
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 *	3.  (anything) ** NAN is NAN
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 *	4.  NAN ** (anything except 0) is NAN
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 *	5.  +-(|x| > 1) **  +INF is +INF
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 *	6.  +-(|x| > 1) **  -INF is +0
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 *	7.  +-(|x| < 1) **  +INF is +0
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 *	8.  +-(|x| < 1) **  -INF is +INF
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 *	9.  +-1         ** +-INF is NAN
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 *	10. +0 ** (+anything except 0, NAN)               is +0
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 *	11. -0 ** (+anything except 0, NAN, odd integer)  is +0
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 *	12. +0 ** (-anything except 0, NAN)               is +INF
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 *	13. -0 ** (-anything except 0, NAN, odd integer)  is +INF
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 *	14. -0 ** (odd integer) = -( +0 ** (odd integer) )
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 *	15. +INF ** (+anything except 0,NAN) is +INF
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 *	16. +INF ** (-anything except 0,NAN) is +0
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 *	17. -INF ** (anything)  = -0 ** (-anything)
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 *	18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
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 *	19. (-anything except 0 and inf) ** (non-integer) is NAN
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 *
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 * Accuracy:
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 *	pow(x,y) returns x**y nearly rounded. In particular
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 *			pow(integer,integer)
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 *	always returns the correct integer provided it is
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 *	representable.
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 *
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 * Constants :
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 * The hexadecimal values are the intended ones for the following
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 * constants. The decimal values may be used, provided that the
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 * compiler will convert from decimal to binary accurately enough
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 * to produce the hexadecimal values shown.
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 */
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/*#include "math.h"*/
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#include "math_private.h"
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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bp[] = {1.0, 1.5,},
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dp_h[] = { 0.0, 5.84962487220764160156e-01,}, /* 0x3FE2B803, 0x40000000 */
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dp_l[] = { 0.0, 1.35003920212974897128e-08,}, /* 0x3E4CFDEB, 0x43CFD006 */
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	/* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */
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L1  =  5.99999999999994648725e-01, /* 0x3FE33333, 0x33333303 */
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L2  =  4.28571428578550184252e-01, /* 0x3FDB6DB6, 0xDB6FABFF */
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L3  =  3.33333329818377432918e-01, /* 0x3FD55555, 0x518F264D */
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L4  =  2.72728123808534006489e-01, /* 0x3FD17460, 0xA91D4101 */
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L5  =  2.30660745775561754067e-01, /* 0x3FCD864A, 0x93C9DB65 */
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L6  =  2.06975017800338417784e-01, /* 0x3FCA7E28, 0x4A454EEF */
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P1   =  1.66666666666666019037e-01, /* 0x3FC55555, 0x5555553E */
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P2   = -2.77777777770155933842e-03, /* 0xBF66C16C, 0x16BEBD93 */
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P3   =  6.61375632143793436117e-05, /* 0x3F11566A, 0xAF25DE2C */
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P4   = -1.65339022054652515390e-06, /* 0xBEBBBD41, 0xC5D26BF1 */
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P5   =  4.13813679705723846039e-08, /* 0x3E663769, 0x72BEA4D0 */
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lg2  =  6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
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lg2_h  =  6.93147182464599609375e-01, /* 0x3FE62E43, 0x00000000 */
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lg2_l  = -1.90465429995776804525e-09, /* 0xBE205C61, 0x0CA86C39 */
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ovt =  8.0085662595372944372e-0017, /* -(1024-log2(ovfl+.5ulp)) */
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cp    =  9.61796693925975554329e-01, /* 0x3FEEC709, 0xDC3A03FD =2/(3ln2) */
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cp_h  =  9.61796700954437255859e-01, /* 0x3FEEC709, 0xE0000000 =(float)cp */
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cp_l  = -7.02846165095275826516e-09, /* 0xBE3E2FE0, 0x145B01F5 =tail of cp_h*/
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ivln2    =  1.44269504088896338700e+00, /* 0x3FF71547, 0x652B82FE =1/ln2 */
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ivln2_h  =  1.44269502162933349609e+00, /* 0x3FF71547, 0x60000000 =24b 1/ln2*/
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ivln2_l  =  1.92596299112661746887e-08; /* 0x3E54AE0B, 0xF85DDF44 =1/ln2 tail*/
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#ifdef __STDC__
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	double __ieee754_pow(double x, double y)
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#else
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	double __ieee754_pow(x,y)
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	double x, y;
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#endif
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{
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	double z,ax,z_h,z_l,p_h,p_l;
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	double y1,t1,t2,r,s,t,u,v,w;
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	int32_t i,j,k,yisint,n;
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	int32_t hx,hy,ix,iy;
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	u_int32_t lx,ly;
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	EXTRACT_WORDS(hx,lx,x);
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	EXTRACT_WORDS(hy,ly,y);
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	ix = hx&0x7fffffff;  iy = hy&0x7fffffff;
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   113
    /* y==zero: x**0 = 1 */
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   114
	if((iy|ly)==0) return one;
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   115
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   116
    /* +-NaN return x+y */
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   117
	if(ix > 0x7ff00000 || ((ix==0x7ff00000)&&(lx!=0)) ||
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   118
	   iy > 0x7ff00000 || ((iy==0x7ff00000)&&(ly!=0)))
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   119
		return x+y;
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   120
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   121
    /* determine if y is an odd int when x < 0
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   122
     * yisint = 0	... y is not an integer
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   123
     * yisint = 1	... y is an odd int
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   124
     * yisint = 2	... y is an even int
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   125
     */
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   126
	yisint  = 0;
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   127
	if(hx<0) {
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   128
	    if(iy>=0x43400000) yisint = 2; /* even integer y */
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   129
	    else if(iy>=0x3ff00000) {
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   130
		k = (iy>>20)-0x3ff;	   /* exponent */
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   131
		if(k>20) {
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   132
		    j = ly>>(52-k);
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   133
		    if((u_int32_t)(j<<(52-k))==ly) yisint = 2-(j&1);
1330
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   134
		} else if(ly==0) {
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   135
		    j = iy>>(20-k);
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   136
		    if((j<<(20-k))==iy) yisint = 2-(j&1);
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   137
		}
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   138
	    }
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   139
	}
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   140
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   141
    /* special value of y */
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   142
	if(ly==0) {
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   143
	    if (iy==0x7ff00000) {	/* y is +-inf */
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   144
	        if(((ix-0x3ff00000)|lx)==0)
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   145
		    return  y - y;	/* inf**+-1 is NaN */
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   146
	        else if (ix >= 0x3ff00000)/* (|x|>1)**+-inf = inf,0 */
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   147
		    return (hy>=0)? y: zero;
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   148
	        else			/* (|x|<1)**-,+inf = inf,0 */
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   149
		    return (hy<0)?-y: zero;
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   150
	    }
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   151
	    if(iy==0x3ff00000) {	/* y is  +-1 */
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   152
		if(hy<0) return one/x; else return x;
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   153
	    }
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   154
	    if(hy==0x40000000) return x*x; /* y is  2 */
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   155
	    if(hy==0x3fe00000) {	/* y is  0.5 */
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   156
		if(hx>=0)	/* x >= +0 */
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   157
		return __ieee754_sqrt(x);
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   158
	    }
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diff changeset
   159
	}
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   160
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   161
	ax   = x < 0 ? -x : x; /*fabs(x);*/
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   162
    /* special value of x */
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   163
	if(lx==0) {
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   164
	    if(ix==0x7ff00000||ix==0||ix==0x3ff00000){
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   165
		z = ax;			/*x is +-0,+-inf,+-1*/
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   166
		if(hy<0) z = one/z;	/* z = (1/|x|) */
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   167
		if(hx<0) {
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diff changeset
   168
		    if(((ix-0x3ff00000)|yisint)==0) {
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   169
			z = (z-z)/(z-z); /* (-1)**non-int is NaN */
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   170
		    } else if(yisint==1)
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   171
			z = -z;		/* (x<0)**odd = -(|x|**odd) */
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   172
		}
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   173
		return z;
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   174
	    }
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   175
	}
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   176
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   177
    /* (x<0)**(non-int) is NaN */
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   178
	if(((((u_int32_t)hx>>31)-1)|yisint)==0) return (x-x)/(x-x);
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   179
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   180
    /* |y| is huge */
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   181
	if(iy>0x41e00000) { /* if |y| > 2**31 */
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   182
	    if(iy>0x43f00000){	/* if |y| > 2**64, must o/uflow */
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   183
		if(ix<=0x3fefffff) return (hy<0)? huge*huge:tiny*tiny;
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   184
		if(ix>=0x3ff00000) return (hy>0)? huge*huge:tiny*tiny;
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   185
	    }
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   186
	/* over/underflow if x is not close to one */
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   187
	    if(ix<0x3fefffff) return (hy<0)? huge*huge:tiny*tiny;
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   188
	    if(ix>0x3ff00000) return (hy>0)? huge*huge:tiny*tiny;
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   189
	/* now |1-x| is tiny <= 2**-20, suffice to compute
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diff changeset
   190
	   log(x) by x-x^2/2+x^3/3-x^4/4 */
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   191
	    t = x-1;		/* t has 20 trailing zeros */
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   192
	    w = (t*t)*(0.5-t*(0.3333333333333333333333-t*0.25));
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   193
	    u = ivln2_h*t;	/* ivln2_h has 21 sig. bits */
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   194
	    v = t*ivln2_l-w*ivln2;
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   195
	    t1 = u+v;
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   196
	    SET_LOW_WORD(t1,0);
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   197
	    t2 = v-(t1-u);
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diff changeset
   198
	} else {
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   199
	    double s2,s_h,s_l,t_h,t_l;
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   200
	    n = 0;
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   201
	/* take care subnormal number */
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   202
	    if(ix<0x00100000)
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   203
		{ax *= two53; n -= 53; GET_HIGH_WORD(ix,ax); }
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   204
	    n  += ((ix)>>20)-0x3ff;
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   205
	    j  = ix&0x000fffff;
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diff changeset
   206
	/* determine interval */
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diff changeset
   207
	    ix = j|0x3ff00000;		/* normalize ix */
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   208
	    if(j<=0x3988E) k=0;		/* |x|<sqrt(3/2) */
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   209
	    else if(j<0xBB67A) k=1;	/* |x|<sqrt(3)   */
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   210
	    else {k=0;n+=1;ix -= 0x00100000;}
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   211
	    SET_HIGH_WORD(ax,ix);
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   212
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   213
	/* compute s = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
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   214
	    u = ax-bp[k];		/* bp[0]=1.0, bp[1]=1.5 */
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   215
	    v = one/(ax+bp[k]);
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   216
	    s = u*v;
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   217
	    s_h = s;
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   218
	    SET_LOW_WORD(s_h,0);
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diff changeset
   219
	/* t_h=ax+bp[k] High */
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   220
	    t_h = zero;
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   221
	    SET_HIGH_WORD(t_h,((ix>>1)|0x20000000)+0x00080000+(k<<18));
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   222
	    t_l = ax - (t_h-bp[k]);
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diff changeset
   223
	    s_l = v*((u-s_h*t_h)-s_h*t_l);
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diff changeset
   224
	/* compute log(ax) */
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   225
	    s2 = s*s;
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   226
	    r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6)))));
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   227
	    r += s_l*(s_h+s);
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   228
	    s2  = s_h*s_h;
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diff changeset
   229
	    t_h = 3.0+s2+r;
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diff changeset
   230
	    SET_LOW_WORD(t_h,0);
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   231
	    t_l = r-((t_h-3.0)-s2);
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   232
	/* u+v = s*(1+...) */
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   233
	    u = s_h*t_h;
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   234
	    v = s_l*t_h+t_l*s;
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	/* 2/(3log2)*(s+...) */
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   236
	    p_h = u+v;
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   237
	    SET_LOW_WORD(p_h,0);
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   238
	    p_l = v-(p_h-u);
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   239
	    z_h = cp_h*p_h;		/* cp_h+cp_l = 2/(3*log2) */
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   240
	    z_l = cp_l*p_h+p_l*cp+dp_l[k];
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   241
	/* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */
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   242
	    t = (double)n;
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   243
	    t1 = (((z_h+z_l)+dp_h[k])+t);
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   244
	    SET_LOW_WORD(t1,0);
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   245
	    t2 = z_l-(((t1-t)-dp_h[k])-z_h);
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   246
	}
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   247
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	s = one; /* s (sign of result -ve**odd) = -1 else = 1 */
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   249
	if(((((u_int32_t)hx>>31)-1)|(yisint-1))==0)
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   250
	    s = -one;/* (-ve)**(odd int) */
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   251
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   252
    /* split up y into y1+y2 and compute (y1+y2)*(t1+t2) */
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   253
	y1  = y;
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   254
	SET_LOW_WORD(y1,0);
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   255
	p_l = (y-y1)*t1+y*t2;
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   256
	p_h = y1*t1;
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   257
	z = p_l+p_h;
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   258
	EXTRACT_WORDS(j,i,z);
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   259
	if (j>=0x40900000) {				/* z >= 1024 */
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   260
	    if(((j-0x40900000)|i)!=0)			/* if z > 1024 */
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   261
		return s*huge*huge;			/* overflow */
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   262
	    else {
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   263
		if(p_l+ovt>z-p_h) return s*huge*huge;	/* overflow */
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   264
	    }
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   265
	} else if((j&0x7fffffff)>=0x4090cc00 ) {	/* z <= -1075 */
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   266
	    if(((j-0xc090cc00)|i)!=0) 		/* z < -1075 */
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   267
		return s*tiny*tiny;		/* underflow */
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diff changeset
   268
	    else {
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   269
		if(p_l<=z-p_h) return s*tiny*tiny;	/* underflow */
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   270
	    }
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   271
	}
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   272
    /*
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   273
     * compute 2**(p_h+p_l)
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   274
     */
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   275
	i = j&0x7fffffff;
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   276
	k = (i>>20)-0x3ff;
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   277
	n = 0;
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   278
	if(i>0x3fe00000) {		/* if |z| > 0.5, set n = [z+0.5] */
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   279
	    n = j+(0x00100000>>(k+1));
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   280
	    k = ((n&0x7fffffff)>>20)-0x3ff;	/* new k for n */
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   281
	    t = zero;
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   282
	    SET_HIGH_WORD(t,n&~(0x000fffff>>k));
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   283
	    n = ((n&0x000fffff)|0x00100000)>>(20-k);
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   284
	    if(j<0) n = -n;
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   285
	    p_h -= t;
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diff changeset
   286
	}
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   287
	t = p_l+p_h;
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   288
	SET_LOW_WORD(t,0);
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   289
	u = t*lg2_h;
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   290
	v = (p_l-(t-p_h))*lg2+t*lg2_l;
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   291
	z = u+v;
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   292
	w = v-(z-u);
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   293
	t  = z*z;
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   294
	t1  = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5))));
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   295
	r  = (z*t1)/(t1-two)-(w+z*w);
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   296
	z  = one-(r-z);
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   297
	GET_HIGH_WORD(j,z);
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   298
	j += (n<<20);
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   299
	if((j>>20)<=0) z = scalbn(z,n);	/* subnormal output */
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   300
	else SET_HIGH_WORD(z,j);
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   301
	return s*z;
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   302
}