1 /* @(#)e_fmod.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, 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 #if defined(LIBM_SCCS) && !defined(lint) 14 static char rcsid[] = "$NetBSD: e_fmod.c,v 1.8 1995/05/10 20:45:07 jtc Exp $"; 15 #endif 16 17 /* 18 * __ieee754_fmod(x,y) 19 * Return x mod y in exact arithmetic 20 * Method: shift and subtract 21 */ 22 23 #include "math.h" 24 #include "math_private.h" 25 26 #ifdef __STDC__ 27 static const double one = 1.0, Zero[] = {0.0, -0.0,}; 28 #else 29 static double one = 1.0, Zero[] = {0.0, -0.0,}; 30 #endif 31 32 #ifdef __STDC__ 33 double __ieee754_fmod(double x, double y) 34 #else 35 double __ieee754_fmod(x,y) 36 double x,y ; 37 #endif 38 { 39 int32_t n,hx,hy,hz,ix,iy,sx,i; 40 u_int32_t lx,ly,lz; 41 42 EXTRACT_WORDS(hx,lx,x); 43 EXTRACT_WORDS(hy,ly,y); 44 sx = hx&0x80000000; /* sign of x */ 45 hx ^=sx; /* |x| */ 46 hy &= 0x7fffffff; /* |y| */ 47 48 /* purge off exception values */ 49 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */ 50 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */ 51 return (x*y)/(x*y); 52 if(hx<=hy) { 53 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */ 54 if(lx==ly) 55 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ 56 } 57 58 /* determine ix = ilogb(x) */ 59 if(hx<0x00100000) { /* subnormal x */ 60 if(hx==0) { 61 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1; 62 } else { 63 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1; 64 } 65 } else ix = (hx>>20)-1023; 66 67 /* determine iy = ilogb(y) */ 68 if(hy<0x00100000) { /* subnormal y */ 69 if(hy==0) { 70 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1; 71 } else { 72 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1; 73 } 74 } else iy = (hy>>20)-1023; 75 76 /* set up {hx,lx}, {hy,ly} and align y to x */ 77 if(ix >= -1022) 78 hx = 0x00100000|(0x000fffff&hx); 79 else { /* subnormal x, shift x to normal */ 80 n = -1022-ix; 81 if(n<=31) { 82 hx = (hx<<n)|(lx>>(32-n)); 83 lx <<= n; 84 } else { 85 hx = lx<<(n-32); 86 lx = 0; 87 } 88 } 89 if(iy >= -1022) 90 hy = 0x00100000|(0x000fffff&hy); 91 else { /* subnormal y, shift y to normal */ 92 n = -1022-iy; 93 if(n<=31) { 94 hy = (hy<<n)|(ly>>(32-n)); 95 ly <<= n; 96 } else { 97 hy = ly<<(n-32); 98 ly = 0; 99 } 100 } 101 102 /* fix point fmod */ 103 n = ix - iy; 104 while(n--) { 105 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 106 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;} 107 else { 108 if((hz|lz)==0) /* return sign(x)*0 */ 109 return Zero[(u_int32_t)sx>>31]; 110 hx = hz+hz+(lz>>31); lx = lz+lz; 111 } 112 } 113 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 114 if(hz>=0) {hx=hz;lx=lz;} 115 116 /* convert back to floating value and restore the sign */ 117 if((hx|lx)==0) /* return sign(x)*0 */ 118 return Zero[(u_int32_t)sx>>31]; 119 while(hx<0x00100000) { /* normalize x */ 120 hx = hx+hx+(lx>>31); lx = lx+lx; 121 iy -= 1; 122 } 123 if(iy>= -1022) { /* normalize output */ 124 hx = ((hx-0x00100000)|((iy+1023)<<20)); 125 INSERT_WORDS(x,hx|sx,lx); 126 } else { /* subnormal output */ 127 n = -1022 - iy; 128 if(n<=20) { 129 lx = (lx>>n)|((u_int32_t)hx<<(32-n)); 130 hx >>= n; 131 } else if (n<=31) { 132 lx = (hx<<(32-n))|(lx>>n); hx = sx; 133 } else { 134 lx = hx>>(n-32); hx = sx; 135 } 136 INSERT_WORDS(x,hx|sx,lx); 137 x *= one; /* create necessary signal */ 138 } 139 return x; /* exact output */ 140 } 141