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
  13 #ifndef lint
  14 static char rcsid[] = "$FreeBSD$";
  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 static const double one = 1.0;
  31
  32 double
  33 modf(double x, double *iptr)
  34 {
  35         int32_t i0,i1,j0;
  36         u_int32_t i;
  37         EXTRACT_WORDS(i0,i1,x);
  38         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  39         if(j0<20) {                     /* integer part in high x */
  40             if(j0<0) {                  /* |x|<1 */
  41                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  42                 return x;
  43             } else {
  44                 i = (0x000fffff)>>j0;
  45                 if(((i0&i)|i1)==0) {            /* x is integral */
  46                     u_int32_t high;
  47                     *iptr = x;
  48                     GET_HIGH_WORD(high,x);
  49                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  50                     return x;
  51                 } else {
  52                     INSERT_WORDS(*iptr,i0&(~i),0);
  53                     return x - *iptr;
  54                 }
  55             }
  56         } else if (j0>51) {             /* no fraction part */
  57             u_int32_t high;
  58             *iptr = x*one;
  59             GET_HIGH_WORD(high,x);
  60             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  61             return x;
  62         } else {                        /* fraction part in low x */
  63             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  64             if((i1&i)==0) {             /* x is integral */
  65                 u_int32_t high;
  66                 *iptr = x;
  67                 GET_HIGH_WORD(high,x);
  68                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  69                 return x;
  70             } else {
  71                 INSERT_WORDS(*iptr,i0,i1&(~i));
  72                 return x - *iptr;
  73             }
  74         }
  75 }