| The Android Open Source Project | 1dc9e47 | 2009-03-03 19:28:35 -0800 | [diff] [blame] | 1 | /* @(#)e_fmod.c 1.3 95/01/18 */ |
| 2 | /*- |
| 3 | * ==================================================== |
| 4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 5 | * |
| 6 | * Developed at SunSoft, a Sun Microsystems, Inc. business. |
| 7 | * Permission to use, copy, modify, and distribute this |
| 8 | * software is freely granted, provided that this notice |
| 9 | * is preserved. |
| 10 | * ==================================================== |
| 11 | */ |
| 12 | |
| 13 | #include <sys/cdefs.h> |
| 14 | /* __FBSDID("$FreeBSD: src/lib/msun/src/s_remquof.c,v 1.1 2005/03/25 04:40:44 das Exp $"); */ |
| 15 | |
| 16 | #include "math.h" |
| 17 | #include "math_private.h" |
| 18 | |
| 19 | static const float Zero[] = {0.0, -0.0,}; |
| 20 | |
| 21 | /* |
| 22 | * Return the IEEE remainder and set *quo to the last n bits of the |
| 23 | * quotient, rounded to the nearest integer. We choose n=31 because |
| 24 | * we wind up computing all the integer bits of the quotient anyway as |
| 25 | * a side-effect of computing the remainder by the shift and subtract |
| 26 | * method. In practice, this is far more bits than are needed to use |
| 27 | * remquo in reduction algorithms. |
| 28 | */ |
| 29 | float |
| 30 | remquof(float x, float y, int *quo) |
| 31 | { |
| 32 | int32_t n,hx,hy,hz,ix,iy,sx,i; |
| 33 | u_int32_t q,sxy; |
| 34 | |
| 35 | GET_FLOAT_WORD(hx,x); |
| 36 | GET_FLOAT_WORD(hy,y); |
| 37 | sxy = (hx ^ hy) & 0x80000000; |
| 38 | sx = hx&0x80000000; /* sign of x */ |
| 39 | hx ^=sx; /* |x| */ |
| 40 | hy &= 0x7fffffff; /* |y| */ |
| 41 | |
| 42 | /* purge off exception values */ |
| 43 | if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */ |
| 44 | return (x*y)/(x*y); |
| 45 | if(hx<hy) { |
| 46 | q = 0; |
| 47 | goto fixup; /* |x|<|y| return x or x-y */ |
| 48 | } else if(hx==hy) { |
| 49 | *quo = 1; |
| 50 | return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ |
| 51 | } |
| 52 | |
| 53 | /* determine ix = ilogb(x) */ |
| 54 | if(hx<0x00800000) { /* subnormal x */ |
| 55 | for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1; |
| 56 | } else ix = (hx>>23)-127; |
| 57 | |
| 58 | /* determine iy = ilogb(y) */ |
| 59 | if(hy<0x00800000) { /* subnormal y */ |
| 60 | for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1; |
| 61 | } else iy = (hy>>23)-127; |
| 62 | |
| 63 | /* set up {hx,lx}, {hy,ly} and align y to x */ |
| 64 | if(ix >= -126) |
| 65 | hx = 0x00800000|(0x007fffff&hx); |
| 66 | else { /* subnormal x, shift x to normal */ |
| 67 | n = -126-ix; |
| 68 | hx <<= n; |
| 69 | } |
| 70 | if(iy >= -126) |
| 71 | hy = 0x00800000|(0x007fffff&hy); |
| 72 | else { /* subnormal y, shift y to normal */ |
| 73 | n = -126-iy; |
| 74 | hy <<= n; |
| 75 | } |
| 76 | |
| 77 | /* fix point fmod */ |
| 78 | n = ix - iy; |
| 79 | q = 0; |
| 80 | while(n--) { |
| 81 | hz=hx-hy; |
| 82 | if(hz<0) hx = hx << 1; |
| 83 | else {hx = hz << 1; q++;} |
| 84 | q <<= 1; |
| 85 | } |
| 86 | hz=hx-hy; |
| 87 | if(hz>=0) {hx=hz;q++;} |
| 88 | |
| 89 | /* convert back to floating value and restore the sign */ |
| 90 | if(hx==0) { /* return sign(x)*0 */ |
| 91 | *quo = (sxy ? -q : q); |
| 92 | return Zero[(u_int32_t)sx>>31]; |
| 93 | } |
| 94 | while(hx<0x00800000) { /* normalize x */ |
| 95 | hx <<= 1; |
| 96 | iy -= 1; |
| 97 | } |
| 98 | if(iy>= -126) { /* normalize output */ |
| 99 | hx = ((hx-0x00800000)|((iy+127)<<23)); |
| 100 | } else { /* subnormal output */ |
| 101 | n = -126 - iy; |
| 102 | hx >>= n; |
| 103 | } |
| 104 | fixup: |
| 105 | SET_FLOAT_WORD(x,hx); |
| 106 | y = fabsf(y); |
| 107 | if (y < 0x1p-125f) { |
| 108 | if (x+x>y || (x+x==y && (q & 1))) { |
| 109 | q++; |
| 110 | x-=y; |
| 111 | } |
| 112 | } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) { |
| 113 | q++; |
| 114 | x-=y; |
| 115 | } |
| 116 | GET_FLOAT_WORD(hx,x); |
| 117 | SET_FLOAT_WORD(x,hx^sx); |
| 118 | q &= 0x7fffffff; |
| 119 | *quo = (sxy ? -q : q); |
| 120 | return x; |
| 121 | } |