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  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. }
  131.