lib/msun/src/s_modf.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * modf(double x, double *iptr)
  14  * return fraction part of x, and return x's integral part in *iptr.
  15  * Method:
  16  *      Bit twiddling.
  17  *
  18  * Exception:
  19  *      No exception.
  20  */
  21
  22 #include "math.h"
  23 #include "math_private.h"
  24
  25 static const double one = 1.0;
  26
  27 double
  28 modf(double x, double *iptr)
  29 {
  30         int32_t i0,i1,j0;
  31         u_int32_t i;
  32         EXTRACT_WORDS(i0,i1,x);
  33         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  34         if(j0<20) {                     /* integer part in high x */
  35             if(j0<0) {                  /* |x|<1 */
  36                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  37                 return x;
  38             } else {
  39                 i = (0x000fffff)>>j0;
  40                 if(((i0&i)|i1)==0) {            /* x is integral */
  41                     u_int32_t high;
  42                     *iptr = x;
  43                     GET_HIGH_WORD(high,x);
  44                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  45                     return x;
  46                 } else {
  47                     INSERT_WORDS(*iptr,i0&(~i),0);
  48                     return x - *iptr;
  49                 }
  50             }
  51         } else if (j0>51) {             /* no fraction part */
  52             u_int32_t high;
  53             if (j0 == 0x400) {          /* inf/NaN */
  54                 *iptr = x;
  55                 return 0.0 / x;
  56             }
  57             *iptr = x*one;
  58             GET_HIGH_WORD(high,x);
  59             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  60             return x;
  61         } else {                        /* fraction part in low x */
  62             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  63             if((i1&i)==0) {             /* x is integral */
  64                 u_int32_t high;
  65                 *iptr = x;
  66                 GET_HIGH_WORD(high,x);
  67                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  68                 return x;
  69             } else {
  70                 INSERT_WORDS(*iptr,i0,i1&(~i));
  71                 return x - *iptr;
  72             }
  73         }
  74 }