e_fmodf.c (2704B)
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 }