1 /*- 2 * ==================================================== 3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 4 * 5 * Developed at SunSoft, a Sun Microsystems, Inc. business. 6 * Permission to use, copy, modify, and distribute this 7 * software is freely granted, provided that this notice 8 * is preserved. 9 * ==================================================== 10 */ 11 12 #include "math.h" 13 #include "math_private.h" 14 15 static const float Zero[] = {0.0, -0.0,}; 16 17 /* 18 * Return the IEEE remainder and set *quo to the last n bits of the 19 * quotient, rounded to the nearest integer. We choose n=31 because 20 * we wind up computing all the integer bits of the quotient anyway as 21 * a side-effect of computing the remainder by the shift and subtract 22 * method. In practice, this is far more bits than are needed to use 23 * remquo in reduction algorithms. 24 */ 25 float 26 remquof(float x, float y, int *quo) 27 { 28 int32_t n,hx,hy,hz,ix,iy,sx,i; 29 u_int32_t q,sxy; 30 31 GET_FLOAT_WORD(hx,x); 32 GET_FLOAT_WORD(hy,y); 33 sxy = (hx ^ hy) & 0x80000000; 34 sx = hx&0x80000000; /* sign of x */ 35 hx ^=sx; /* |x| */ 36 hy &= 0x7fffffff; /* |y| */ 37 38 /* purge off exception values */ 39 if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */ 40 return nan_mix_op(x, y, *)/nan_mix_op(x, y, *); 41 if(hx<hy) { 42 q = 0; 43 goto fixup; /* |x|<|y| return x or x-y */ 44 } else if(hx==hy) { 45 *quo = (sxy ? -1 : 1); 46 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ 47 } 48 49 /* determine ix = ilogb(x) */ 50 if(hx<0x00800000) { /* subnormal x */ 51 for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1; 52 } else ix = (hx>>23)-127; 53 54 /* determine iy = ilogb(y) */ 55 if(hy<0x00800000) { /* subnormal y */ 56 for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1; 57 } else iy = (hy>>23)-127; 58 59 /* set up {hx,lx}, {hy,ly} and align y to x */ 60 if(ix >= -126) 61 hx = 0x00800000|(0x007fffff&hx); 62 else { /* subnormal x, shift x to normal */ 63 n = -126-ix; 64 hx <<= n; 65 } 66 if(iy >= -126) 67 hy = 0x00800000|(0x007fffff&hy); 68 else { /* subnormal y, shift y to normal */ 69 n = -126-iy; 70 hy <<= n; 71 } 72 73 /* fix point fmod */ 74 n = ix - iy; 75 q = 0; 76 while(n--) { 77 hz=hx-hy; 78 if(hz<0) hx = hx << 1; 79 else {hx = hz << 1; q++;} 80 q <<= 1; 81 } 82 hz=hx-hy; 83 if(hz>=0) {hx=hz;q++;} 84 85 /* convert back to floating value and restore the sign */ 86 if(hx==0) { /* return sign(x)*0 */ 87 q &= 0x7fffffff; 88 *quo = (sxy ? -q : q); 89 return Zero[(u_int32_t)sx>>31]; 90 } 91 while(hx<0x00800000) { /* normalize x */ 92 hx <<= 1; 93 iy -= 1; 94 } 95 if(iy>= -126) { /* normalize output */ 96 hx = ((hx-0x00800000)|((iy+127)<<23)); 97 } else { /* subnormal output */ 98 n = -126 - iy; 99 hx >>= n; 100 } 101 fixup: 102 SET_FLOAT_WORD(x,hx); 103 y = fabsf(y); 104 if (y < 0x1p-125f) { 105 if (x+x>y || (x+x==y && (q & 1))) { 106 q++; 107 x-=y; 108 } 109 } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) { 110 q++; 111 x-=y; 112 } 113 GET_FLOAT_WORD(hx,x); 114 SET_FLOAT_WORD(x,hx^sx); 115 q &= 0x7fffffff; 116 *quo = (sxy ? -q : q); 117 return x; 118 } 119