newlib/libm/common/sf_remquo.c

   1 /* Adapted for Newlib, 2009.  (Allow for int < 32 bits; return *quo=0 during
   2  * errors to make test scripts easier.)  */
   3 /* @(#)e_fmod.c 1.3 95/01/18 */
   4 /*-
   5  * ====================================================
   6  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   7  *
   8  * Developed at SunSoft, a Sun Microsystems, Inc. business.
   9  * Permission to use, copy, modify, and distribute this
  10  * software is freely granted, provided that this notice
  11  * is preserved.
  12  * ====================================================
  13  */
  14
  15 #include <math.h>
  16 #include "fdlibm.h"
  17
  18 /* For quotient, return either all 31 bits that can from calculation (using
  19  * int32_t), or as many as can fit into an int that is smaller than 32 bits.  */
  20 #if INT_MAX > 0x7FFFFFFFL
  21   #define QUO_MASK 0x7FFFFFFF
  22 # else
  23   #define QUO_MASK INT_MAX
  24 #endif
  25
  26 static const float Zero[] = {0.0, -0.0,};
  27
  28 /*
  29  * Return the IEEE remainder and set *quo to the last n bits of the
  30  * quotient, rounded to the nearest integer.  We choose n=31--if that many fit--
  31  * we wind up computing all the integer bits of the quotient anyway as
  32  * a side-effect of computing the remainder by the shift and subtract
  33  * method.  In practice, this is far more bits than are needed to use
  34  * remquo in reduction algorithms.
  35  */
  36 float
  37 remquof(float x, float y, int *quo)
  38 {
  39         __int32_t n,hx,hy,hz,ix,iy,sx,i;
  40         __uint32_t q,sxy;
  41
  42         GET_FLOAT_WORD(hx,x);
  43         GET_FLOAT_WORD(hy,y);
  44         sxy = (hx ^ hy) & 0x80000000;
  45         sx = hx&0x80000000;             /* sign of x */
  46         hx ^=sx;                /* |x| */
  47         hy &= 0x7fffffff;       /* |y| */
  48
  49     /* purge off exception values */
  50         if(hy==0||hx>=0x7f800000||hy>0x7f800000) { /* y=0,NaN;or x not finite */
  51             *quo = 0;   /* Not necessary, but return consistent value */
  52             return (x*y)/(x*y);
  53         }
  54         if(hx<hy) {
  55             q = 0;
  56             goto fixup; /* |x|<|y| return x or x-y */
  57         } else if(hx==hy) {
  58             *quo = 1;
  59             return Zero[(__uint32_t)sx>>31];    /* |x|=|y| return x*0*/
  60         }
  61
  62     /* determine ix = ilogb(x) */
  63         if(hx<0x00800000) {     /* subnormal x */
  64             for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
  65         } else ix = (hx>>23)-127;
  66
  67     /* determine iy = ilogb(y) */
  68         if(hy<0x00800000) {     /* subnormal y */
  69             for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
  70         } else iy = (hy>>23)-127;
  71
  72     /* set up {hx,lx}, {hy,ly} and align y to x */
  73         if(ix >= -126)
  74             hx = 0x00800000|(0x007fffff&hx);
  75         else {          /* subnormal x, shift x to normal */
  76             n = -126-ix;
  77             hx <<= n;
  78         }
  79         if(iy >= -126)
  80             hy = 0x00800000|(0x007fffff&hy);
  81         else {          /* subnormal y, shift y to normal */
  82             n = -126-iy;
  83             hy <<= n;
  84         }
  85
  86     /* fix point fmod */
  87         n = ix - iy;
  88         q = 0;
  89         while(n--) {
  90             hz=hx-hy;
  91             if(hz<0) hx = hx << 1;
  92             else {hx = hz << 1; q++;}
  93             q <<= 1;
  94         }
  95         hz=hx-hy;
  96         if(hz>=0) {hx=hz;q++;}
  97
  98     /* convert back to floating value and restore the sign */
  99         if(hx==0) {                             /* return sign(x)*0 */
 100             *quo = (sxy ? -q : q);
 101             return Zero[(__uint32_t)sx>>31];
 102         }
 103         while(hx<0x00800000) {          /* normalize x */
 104             hx <<= 1;
 105             iy -= 1;
 106         }
 107         if(iy>= -126) {         /* normalize output */
 108             hx = ((hx-0x00800000)|((iy+127)<<23));
 109         } else {                /* subnormal output */
 110             n = -126 - iy;
 111             hx >>= n;
 112         }
 113 fixup:
 114         SET_FLOAT_WORD(x,hx);
 115         y = fabsf(y);
 116         if (y < 0x1p-125f) {
 117             if (x+x>y || (x+x==y && (q & 1))) {
 118                 q++;
 119                 x-=y;
 120             }
 121         } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
 122             q++;
 123             x-=y;
 124         }
 125         GET_FLOAT_WORD(hx,x);
 126         SET_FLOAT_WORD(x,hx^sx);
 127         q &= 0x7fffffff;
 128         *quo = (sxy ? -q : q);
 129         return x;
 130 }