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 } 141
