libm/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 modf(double x, double *iptr)
  28 {
  29         int32_t i0,i1,j0;
  30         u_int32_t i;
  31         EXTRACT_WORDS(i0,i1,x);
  32         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  33         if(j0<20) {                     /* integer part in high x */
  34             if(j0<0) {                  /* |x|<1 */
  35                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  36                 return x;
  37             } else {
  38                 i = (0x000fffff)>>j0;
  39                 if(((i0&i)|i1)==0) {            /* x is integral */
  40                     u_int32_t high;
  41                     *iptr = x;
  42                     GET_HIGH_WORD(high,x);
  43                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  44                     return x;
  45                 } else {
  46                     INSERT_WORDS(*iptr,i0&(~i),0);
  47                     return x - *iptr;
  48                 }
  49             }
  50         } else if (j0>51) {             /* no fraction part */
  51             u_int32_t high;
  52             *iptr = x*one;
  53             GET_HIGH_WORD(high,x);
  54             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  55             return x;
  56         } else {                        /* fraction part in low x */
  57             i = ((u_int32_t)(0xffffffff))>>(j0-20);
  58             if((i1&i)==0) {             /* x is integral */
  59                 u_int32_t high;
  60                 *iptr = x;
  61                 GET_HIGH_WORD(high,x);
  62                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  63                 return x;
  64             } else {
  65                 INSERT_WORDS(*iptr,i0,i1&(~i));
  66                 return x - *iptr;
  67             }
  68         }
  69 }
  70 libm_hidden_def(modf)