sysdeps/libm-ieee754/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
  13 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: s_modf.c,v 1.8 1995/05/10 20:47:55 jtc Exp $";
  15 #endif
  16
  17 /*
  18  * modf(double x, double *iptr)
  19  * return fraction part of x, and return x's integral part in *iptr.
  20  * Method:
  21  *      Bit twiddling.
  22  *
  23  * Exception:
  24  *      No exception.
  25  */
  26
  27 #include "math.h"
  28 #include "math_private.h"
  29
  30 #ifdef __STDC__
  31 static const double one = 1.0;
  32 #else
  33 static double one = 1.0;
  34 #endif
  35
  36 #ifdef __STDC__
  37         double __modf(double x, double *iptr)
  38 #else
  39         double __modf(x, iptr)
  40         double x,*iptr;
  41 #endif
  42 {
  43         int32_t i0,i1,j0;
  44         u_int32_t i;
  45         EXTRACT_WORDS(i0,i1,x);
  46         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  47         if(j0<20) {                     /* integer part in high x */
  48             if(j0<0) {                  /* |x|<1 */
  49                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  50                 return x;
  51             } else {
  52                 i = (0x000fffff)>>j0;
  53                 if(((i0&i)|i1)==0) {            /* x is integral */
  54                     *iptr = x;
  55                     INSERT_WORDS(x,i0&0x80000000,0);    /* return +-0 */
  56                     return x;
  57                 } else {
  58                     INSERT_WORDS(*iptr,i0&(~i),0);
  59                     return x - *iptr;
  60                 }
  61             }
  62         } else if (j0>51) {             /* no fraction part */
  63             u_int32_t high;
  64             *iptr = x*one;
  65             /* We must handle NaNs separately.  */
  66             if (j0 == 0x400 && ((i0 & 0xfffff) | i1))
  67               return x*one;
  68             INSERT_WORDS(x,i0&0x80000000,0);    /* return +-0 */
  69             return x;
  70         } else {                        /* fraction part in low x */
  71             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  72             if((i1&i)==0) {             /* x is integral */
  73                 u_int32_t high;
  74                 *iptr = x;
  75                 GET_HIGH_WORD(high,x);
  76                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  77                 return x;
  78             } else {
  79                 INSERT_WORDS(*iptr,i0,i1&(~i));
  80                 return x - *iptr;
  81             }
  82         }
  83 }
  84 weak_alias (__modf, modf)
  85 #ifdef NO_LONG_DOUBLE
  86 strong_alias (__modf, __modfl)
  87 weak_alias (__modf, modfl)
  88 #endif