sysdeps/ieee754/dbl-64/s_modf.c

   1 /* Rewritten for 64-bit machines by Ulrich Drepper <drepper@gmail.com>.  */
   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 #include <libm-alias-double.h>
  26 #include <stdint.h>
  27
  28 static const double one = 1.0;
  29
  30 double
  31 __modf(double x, double *iptr)
  32 {
  33         int64_t i0;
  34         int32_t j0;
  35         EXTRACT_WORDS64(i0,x);
  36         j0 = ((i0>>52)&0x7ff)-0x3ff;    /* exponent of x */
  37         if(j0<52) {                     /* integer part in x */
  38             if(j0<0) {                  /* |x|<1 */
  39                 /* *iptr = +-0 */
  40                 INSERT_WORDS64(*iptr,i0&UINT64_C(0x8000000000000000));
  41                 return x;
  42             } else {
  43                 uint64_t i = UINT64_C(0x000fffffffffffff)>>j0;
  44                 if((i0&i)==0) {         /* x is integral */
  45                     *iptr = x;
  46                     /* return +-0 */
  47                     INSERT_WORDS64(x,i0&UINT64_C(0x8000000000000000));
  48                     return x;
  49                 } else {
  50                     INSERT_WORDS64(*iptr,i0&(~i));
  51                     return x - *iptr;
  52                 }
  53             }
  54         } else { /* no fraction part */
  55             *iptr = x*one;
  56             /* We must handle NaNs separately.  */
  57             if (j0 == 0x400 && (i0 & UINT64_C(0xfffffffffffff)))
  58               return x*one;
  59             INSERT_WORDS64(x,i0&UINT64_C(0x8000000000000000));  /* return +-0 */
  60             return x;
  61         }
  62 }
  63 #ifndef __modf
  64 libm_alias_double (__modf, modf)
  65 #endif