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 /*
  14  * modf(double x, double *iptr)
  15  * return fraction part of x, and return x's integral part in *iptr.
  16  * Method:
  17  *      Bit twiddling.
  18  *
  19  * Exception:
  20  *      No exception.
  21  */
  22
  23 #include "math.h"
  24 #include "math_private.h"
  25
  26 static const double one = 1.0;
  27
  28 double
  29 modf(double x, double *iptr)
  30 {
  31         int32_t i0,i1,j0;
  32         u_int32_t i;
  33         EXTRACT_WORDS(i0,i1,x);
  34         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  35         if(j0<20) {                     /* integer part in high x */
  36             if(j0<0) {                  /* |x|<1 */
  37                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  38                 return x;
  39             } else {
  40                 i = (0x000fffff)>>j0;
  41                 if(((i0&i)|i1)==0) {            /* x is integral */
  42                     u_int32_t high;
  43                     *iptr = x;
  44                     GET_HIGH_WORD(high,x);
  45                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  46                     return x;
  47                 } else {
  48                     INSERT_WORDS(*iptr,i0&(~i),0);
  49                     return x - *iptr;
  50                 }
  51             }
  52         } else if (j0>51) {             /* no fraction part */
  53             u_int32_t high;
  54             if (j0 == 0x400) {          /* inf/NaN */
  55                 *iptr = x;
  56                 return 0.0 / x;
  57             }
  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 }