sysdeps/ieee754/dbl-64/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 #include <libm-alias-double.h>
  25 #include <stdint.h>
  26
  27 static const double one = 1.0;
  28
  29 double
  30 __modf(double x, double *iptr)
  31 {
  32         int64_t i0;
  33         int32_t j0;
  34         EXTRACT_WORDS64(i0,x);
  35         j0 = ((i0>>52)&0x7ff)-0x3ff;    /* exponent of x */
  36         if(j0<52) {                     /* integer part in x */
  37             if(j0<0) {                  /* |x|<1 */
  38                 /* *iptr = +-0 */
  39                 INSERT_WORDS64(*iptr,i0&UINT64_C(0x8000000000000000));
  40                 return x;
  41             } else {
  42                 uint64_t i = UINT64_C(0x000fffffffffffff)>>j0;
  43                 if((i0&i)==0) {         /* x is integral */
  44                     *iptr = x;
  45                     /* return +-0 */
  46                     INSERT_WORDS64(x,i0&UINT64_C(0x8000000000000000));
  47                     return x;
  48                 } else {
  49                     INSERT_WORDS64(*iptr,i0&(~i));
  50                     return x - *iptr;
  51                 }
  52             }
  53         } else { /* no fraction part */
  54             *iptr = x*one;
  55             /* We must handle NaNs separately.  */
  56             if (j0 == 0x400 && (i0 & UINT64_C(0xfffffffffffff)))
  57               return x*one;
  58             INSERT_WORDS64(x,i0&UINT64_C(0x8000000000000000));  /* return +-0 */
  59             return x;
  60         }
  61 }
  62 #ifndef __modf
  63 libm_alias_double (__modf, modf)
  64 #endif