lib/libm/src/s_modf.c

   1 /* @(#)s_modf.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  * FreeBSD SVN: 165838 (2007-01-06)
  13  */
  14
  15 /*
  16  * modf(double x, double *iptr)
  17  * return fraction part of x, and return x's integral part in *iptr.
  18  * Method:
  19  *      Bit twiddling.
  20  *
  21  * Exception:
  22  *      No exception.
  23  */
  24
  25 #include <math.h>
  26 #include "math_private.h"
  27
  28 static const double one = 1.0;
  29
  30 double
  31 modf(double x, double *iptr)
  32 {
  33         int32_t i0,i1,j0;
  34         u_int32_t i;
  35         EXTRACT_WORDS(i0,i1,x);
  36         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  37         if(j0<20) {                     /* integer part in high x */
  38             if(j0<0) {                  /* |x|<1 */
  39                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  40                 return x;
  41             } else {
  42                 i = (0x000fffff)>>j0;
  43                 if(((i0&i)|i1)==0) {            /* x is integral */
  44                     u_int32_t high;
  45                     *iptr = x;
  46                     GET_HIGH_WORD(high,x);
  47                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  48                     return x;
  49                 } else {
  50                     INSERT_WORDS(*iptr,i0&(~i),0);
  51                     return x - *iptr;
  52                 }
  53             }
  54         } else if (j0>51) {             /* no fraction part */
  55             u_int32_t high;
  56             if (j0 == 0x400) {          /* inf/NaN */
  57                 *iptr = x;
  58                 return 0.0 / x;
  59             }
  60             *iptr = x*one;
  61             GET_HIGH_WORD(high,x);
  62             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  63             return x;
  64         } else {                        /* fraction part in low x */
  65             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  66             if((i1&i)==0) {             /* x is integral */
  67                 u_int32_t high;
  68                 *iptr = x;
  69                 GET_HIGH_WORD(high,x);
  70                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  71                 return x;
  72             } else {
  73                 INSERT_WORDS(*iptr,i0,i1&(~i));
  74                 return x - *iptr;
  75             }
  76         }
  77 }