lib/msun/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: src/lib/msun/src/s_modf.c,v 1.5 1999/08/28 00:06:53 peter Exp $
  13  * $DragonFly: src/lib/msun/src/Attic/s_modf.c,v 1.2 2003/06/17 04:26:53 dillon Exp $
  14  */
  15
  16 /*
  17  * modf(double x, double *iptr)
  18  * return fraction part of x, and return x's integral part in *iptr.
  19  * Method:
  20  *      Bit twiddling.
  21  *
  22  * Exception:
  23  *      No exception.
  24  */
  25
  26 #include "math.h"
  27 #include "math_private.h"
  28
  29 #ifdef __STDC__
  30 static const double one = 1.0;
  31 #else
  32 static double one = 1.0;
  33 #endif
  34
  35 #ifdef __STDC__
  36         double modf(double x, double *iptr)
  37 #else
  38         double modf(x, iptr)
  39         double x,*iptr;
  40 #endif
  41 {
  42         int32_t i0,i1,j0;
  43         u_int32_t i;
  44         EXTRACT_WORDS(i0,i1,x);
  45         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  46         if(j0<20) {                     /* integer part in high x */
  47             if(j0<0) {                  /* |x|<1 */
  48                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  49                 return x;
  50             } else {
  51                 i = (0x000fffff)>>j0;
  52                 if(((i0&i)|i1)==0) {            /* x is integral */
  53                     u_int32_t high;
  54                     *iptr = x;
  55                     GET_HIGH_WORD(high,x);
  56                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  57                     return x;
  58                 } else {
  59                     INSERT_WORDS(*iptr,i0&(~i),0);
  60                     return x - *iptr;
  61                 }
  62             }
  63         } else if (j0>51) {             /* no fraction part */
  64             u_int32_t high;
  65             *iptr = x*one;
  66             GET_HIGH_WORD(high,x);
  67             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  68             return x;
  69         } else {                        /* fraction part in low x */
  70             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  71             if((i1&i)==0) {             /* x is integral */
  72                 u_int32_t high;
  73                 *iptr = x;
  74                 GET_HIGH_WORD(high,x);
  75                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  76                 return x;
  77             } else {
  78                 INSERT_WORDS(*iptr,i0,i1&(~i));
  79                 return x - *iptr;
  80             }
  81         }
  82 }