| The Android Open Source Project | a27d2ba | 2008-10-21 07:00:00 -0700 | [diff] [blame^] | 1 | /* e_fmodf.c -- float version of e_fmod.c. |
| 2 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
| 3 | */ |
| 4 | |
| 5 | /* |
| 6 | * ==================================================== |
| 7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 8 | * |
| 9 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
| 10 | * Permission to use, copy, modify, and distribute this |
| 11 | * software is freely granted, provided that this notice |
| 12 | * is preserved. |
| 13 | * ==================================================== |
| 14 | */ |
| 15 | |
| 16 | #ifndef lint |
| 17 | static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmodf.c,v 1.6 2002/05/28 17:03:12 alfred Exp $"; |
| 18 | #endif |
| 19 | |
| 20 | /* |
| 21 | * __ieee754_fmodf(x,y) |
| 22 | * Return x mod y in exact arithmetic |
| 23 | * Method: shift and subtract |
| 24 | */ |
| 25 | |
| 26 | #include "math.h" |
| 27 | #include "math_private.h" |
| 28 | |
| 29 | static const float one = 1.0, Zero[] = {0.0, -0.0,}; |
| 30 | |
| 31 | float |
| 32 | __ieee754_fmodf(float x, float y) |
| 33 | { |
| 34 | int32_t n,hx,hy,hz,ix,iy,sx,i; |
| 35 | |
| 36 | GET_FLOAT_WORD(hx,x); |
| 37 | GET_FLOAT_WORD(hy,y); |
| 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)|| /* y=0,or x not finite */ |
| 44 | (hy>0x7f800000)) /* or y is NaN */ |
| 45 | return (x*y)/(x*y); |
| 46 | if(hx<hy) return x; /* |x|<|y| return x */ |
| 47 | if(hx==hy) |
| 48 | return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ |
| 49 | |
| 50 | /* determine ix = ilogb(x) */ |
| 51 | if(hx<0x00800000) { /* subnormal x */ |
| 52 | for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1; |
| 53 | } else ix = (hx>>23)-127; |
| 54 | |
| 55 | /* determine iy = ilogb(y) */ |
| 56 | if(hy<0x00800000) { /* subnormal y */ |
| 57 | for (iy = -126,i=(hy<<8); i>=0; i<<=1) iy -=1; |
| 58 | } else iy = (hy>>23)-127; |
| 59 | |
| 60 | /* set up {hx,lx}, {hy,ly} and align y to x */ |
| 61 | if(ix >= -126) |
| 62 | hx = 0x00800000|(0x007fffff&hx); |
| 63 | else { /* subnormal x, shift x to normal */ |
| 64 | n = -126-ix; |
| 65 | hx = hx<<n; |
| 66 | } |
| 67 | if(iy >= -126) |
| 68 | hy = 0x00800000|(0x007fffff&hy); |
| 69 | else { /* subnormal y, shift y to normal */ |
| 70 | n = -126-iy; |
| 71 | hy = hy<<n; |
| 72 | } |
| 73 | |
| 74 | /* fix point fmod */ |
| 75 | n = ix - iy; |
| 76 | while(n--) { |
| 77 | hz=hx-hy; |
| 78 | if(hz<0){hx = hx+hx;} |
| 79 | else { |
| 80 | if(hz==0) /* return sign(x)*0 */ |
| 81 | return Zero[(u_int32_t)sx>>31]; |
| 82 | hx = hz+hz; |
| 83 | } |
| 84 | } |
| 85 | hz=hx-hy; |
| 86 | if(hz>=0) {hx=hz;} |
| 87 | |
| 88 | /* convert back to floating value and restore the sign */ |
| 89 | if(hx==0) /* return sign(x)*0 */ |
| 90 | return Zero[(u_int32_t)sx>>31]; |
| 91 | while(hx<0x00800000) { /* normalize x */ |
| 92 | hx = hx+hx; |
| 93 | iy -= 1; |
| 94 | } |
| 95 | if(iy>= -126) { /* normalize output */ |
| 96 | hx = ((hx-0x00800000)|((iy+127)<<23)); |
| 97 | SET_FLOAT_WORD(x,hx|sx); |
| 98 | } else { /* subnormal output */ |
| 99 | n = -126 - iy; |
| 100 | hx >>= n; |
| 101 | SET_FLOAT_WORD(x,hx|sx); |
| 102 | x *= one; /* create necessary signal */ |
| 103 | } |
| 104 | return x; /* exact output */ |
| 105 | } |