The Android Open Source Project | b07e1d9 | 2009-03-03 19:29:30 -0800 | [diff] [blame] | 1 | |
| 2 | /* @(#)e_fmod.c 1.3 95/01/18 */ |
| 3 | /* |
| 4 | * ==================================================== |
| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 6 | * |
| 7 | * Developed at SunSoft, a Sun Microsystems, Inc. business. |
| 8 | * Permission to use, copy, modify, and distribute this |
| 9 | * software is freely granted, provided that this notice |
| 10 | * is preserved. |
| 11 | * ==================================================== |
| 12 | */ |
| 13 | |
| 14 | /* |
| 15 | * __ieee754_fmod(x,y) |
| 16 | * Return x mod y in exact arithmetic |
| 17 | * Method: shift and subtract |
| 18 | */ |
| 19 | |
| 20 | #include "fdlibm.h" |
| 21 | |
| 22 | #ifdef __STDC__ |
| 23 | static const double one = 1.0, Zero[] = {0.0, -0.0,}; |
| 24 | #else |
| 25 | static double one = 1.0, Zero[] = {0.0, -0.0,}; |
| 26 | #endif |
| 27 | |
| 28 | #ifdef __STDC__ |
| 29 | double __ieee754_fmod(double x, double y) |
| 30 | #else |
| 31 | double __ieee754_fmod(x,y) |
| 32 | double x,y ; |
| 33 | #endif |
| 34 | { |
| 35 | int n,hx,hy,hz,ix,iy,sx,i; |
| 36 | unsigned lx,ly,lz; |
| 37 | |
| 38 | hx = __HI(x); /* high word of x */ |
| 39 | lx = __LO(x); /* low word of x */ |
| 40 | hy = __HI(y); /* high word of y */ |
| 41 | ly = __LO(y); /* low word of y */ |
| 42 | sx = hx&0x80000000; /* sign of x */ |
| 43 | hx ^=sx; /* |x| */ |
| 44 | hy &= 0x7fffffff; /* |y| */ |
| 45 | |
| 46 | /* purge off exception values */ |
| 47 | if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */ |
| 48 | ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */ |
| 49 | return (x*y)/(x*y); |
| 50 | if(hx<=hy) { |
| 51 | if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */ |
| 52 | if(lx==ly) |
| 53 | return Zero[(unsigned)sx>>31]; /* |x|=|y| return x*0*/ |
| 54 | } |
| 55 | |
| 56 | /* determine ix = ieee_ilogb(x) */ |
| 57 | if(hx<0x00100000) { /* subnormal x */ |
| 58 | if(hx==0) { |
| 59 | for (ix = -1043, i=lx; i>0; i<<=1) ix -=1; |
| 60 | } else { |
| 61 | for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1; |
| 62 | } |
| 63 | } else ix = (hx>>20)-1023; |
| 64 | |
| 65 | /* determine iy = ieee_ilogb(y) */ |
| 66 | if(hy<0x00100000) { /* subnormal y */ |
| 67 | if(hy==0) { |
| 68 | for (iy = -1043, i=ly; i>0; i<<=1) iy -=1; |
| 69 | } else { |
| 70 | for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1; |
| 71 | } |
| 72 | } else iy = (hy>>20)-1023; |
| 73 | |
| 74 | /* set up {hx,lx}, {hy,ly} and align y to x */ |
| 75 | if(ix >= -1022) |
| 76 | hx = 0x00100000|(0x000fffff&hx); |
| 77 | else { /* subnormal x, shift x to normal */ |
| 78 | n = -1022-ix; |
| 79 | if(n<=31) { |
| 80 | hx = (hx<<n)|(lx>>(32-n)); |
| 81 | lx <<= n; |
| 82 | } else { |
| 83 | hx = lx<<(n-32); |
| 84 | lx = 0; |
| 85 | } |
| 86 | } |
| 87 | if(iy >= -1022) |
| 88 | hy = 0x00100000|(0x000fffff&hy); |
| 89 | else { /* subnormal y, shift y to normal */ |
| 90 | n = -1022-iy; |
| 91 | if(n<=31) { |
| 92 | hy = (hy<<n)|(ly>>(32-n)); |
| 93 | ly <<= n; |
| 94 | } else { |
| 95 | hy = ly<<(n-32); |
| 96 | ly = 0; |
| 97 | } |
| 98 | } |
| 99 | |
| 100 | /* fix point fmod */ |
| 101 | n = ix - iy; |
| 102 | while(n--) { |
| 103 | hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; |
| 104 | if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;} |
| 105 | else { |
| 106 | if((hz|lz)==0) /* return sign(x)*0 */ |
| 107 | return Zero[(unsigned)sx>>31]; |
| 108 | hx = hz+hz+(lz>>31); lx = lz+lz; |
| 109 | } |
| 110 | } |
| 111 | hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; |
| 112 | if(hz>=0) {hx=hz;lx=lz;} |
| 113 | |
| 114 | /* convert back to floating value and restore the sign */ |
| 115 | if((hx|lx)==0) /* return sign(x)*0 */ |
| 116 | return Zero[(unsigned)sx>>31]; |
| 117 | while(hx<0x00100000) { /* normalize x */ |
| 118 | hx = hx+hx+(lx>>31); lx = lx+lx; |
| 119 | iy -= 1; |
| 120 | } |
| 121 | if(iy>= -1022) { /* normalize output */ |
| 122 | hx = ((hx-0x00100000)|((iy+1023)<<20)); |
| 123 | __HI(x) = hx|sx; |
| 124 | __LO(x) = lx; |
| 125 | } else { /* subnormal output */ |
| 126 | n = -1022 - iy; |
| 127 | if(n<=20) { |
| 128 | lx = (lx>>n)|((unsigned)hx<<(32-n)); |
| 129 | hx >>= n; |
| 130 | } else if (n<=31) { |
| 131 | lx = (hx<<(32-n))|(lx>>n); hx = sx; |
| 132 | } else { |
| 133 | lx = hx>>(n-32); hx = sx; |
| 134 | } |
| 135 | __HI(x) = hx|sx; |
| 136 | __LO(x) = lx; |
| 137 | x *= one; /* create necessary signal */ |
| 138 | } |
| 139 | return x; /* exact output */ |
| 140 | } |