libm/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 libm_hidden_proto(modf)
  37 #ifdef __STDC__
  38         double modf(double x, double *iptr)
  39 #else
  40         double modf(x, iptr)
  41         double x,*iptr;
  42 #endif
  43 {
  44         int32_t i0,i1,j0;
  45         u_int32_t i;
  46         EXTRACT_WORDS(i0,i1,x);
  47         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  48         if(j0<20) {                     /* integer part in high x */
  49             if(j0<0) {                  /* |x|<1 */
  50                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  51                 return x;
  52             } else {
  53                 i = (0x000fffff)>>j0;
  54                 if(((i0&i)|i1)==0) {            /* x is integral */
  55                     u_int32_t high;
  56                     *iptr = x;
  57                     GET_HIGH_WORD(high,x);
  58                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  59                     return x;
  60                 } else {
  61                     INSERT_WORDS(*iptr,i0&(~i),0);
  62                     return x - *iptr;
  63                 }
  64             }
  65         } else if (j0>51) {             /* no fraction part */
  66             u_int32_t high;
  67             *iptr = x*one;
  68             GET_HIGH_WORD(high,x);
  69             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  70             return x;
  71         } else {                        /* fraction part in low x */
  72             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  73             if((i1&i)==0) {             /* x is integral */
  74                 u_int32_t high;
  75                 *iptr = x;
  76                 GET_HIGH_WORD(high,x);
  77                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  78                 return x;
  79             } else {
  80                 INSERT_WORDS(*iptr,i0,i1&(~i));
  81                 return x - *iptr;
  82             }
  83         }
  84 }
  85 libm_hidden_def(modf)