lib/libm/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 #include <sys/cdefs.h>
  14 #if defined(LIBM_SCCS) && !defined(lint)
  15 __RCSID("$NetBSD: s_modf.c,v 1.15 2014/06/16 12:54:43 joerg Exp $");
  16 #endif
  17
  18 /*
  19  * modf(double x, double *iptr)
  20  * return fraction part of x, and return x's integral part in *iptr.
  21  * Method:
  22  *      Bit twiddling.
  23  *
  24  * Exception:
  25  *      No exception.
  26  */
  27
  28 #include "math.h"
  29 #include "math_private.h"
  30
  31 static const double one = 1.0;
  32
  33 #ifndef __HAVE_LONG_DOUBLE
  34 __strong_alias(_modfl, modf)
  35 __weak_alias(modfl, modf)
  36 #endif
  37
  38 double
  39 modf(double x, double *iptr)
  40 {
  41         int32_t i0,i1,jj0;
  42         u_int32_t i;
  43         EXTRACT_WORDS(i0,i1,x);
  44         jj0 = (((uint32_t)i0>>20)&0x7ff)-0x3ff; /* exponent of x */
  45         if(jj0<20) {                    /* integer part in high x */
  46             if(jj0<0) {                 /* |x|<1 */
  47                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  48                 return x;
  49             } else {
  50                 i = (0x000fffff)>>jj0;
  51                 if(((i0&i)|i1)==0) {            /* x is integral */
  52                     u_int32_t high;
  53                     *iptr = x;
  54                     GET_HIGH_WORD(high,x);
  55                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  56                     return x;
  57                 } else {
  58                     INSERT_WORDS(*iptr,i0&(~i),0);
  59                     return x - *iptr;
  60                 }
  61             }
  62         } else if (jj0>51) {            /* no fraction part */
  63             u_int32_t high;
  64             *iptr = x*one;
  65             if (jj0 == 0x400)           /* +-inf or NaN */
  66                 return 0.0 / x;         /* +-0 or NaN */
  67             GET_HIGH_WORD(high,x);
  68             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
  69             return x;
  70         } else {                        /* fraction part in low x */
  71             i = ((u_int32_t)(0xffffffff))>>(jj0-20);
  72             if((i1&i)==0) {             /* x is integral */
  73                 u_int32_t high;
  74                 *iptr = x;
  75                 GET_HIGH_WORD(high,x);
  76                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
  77                 return x;
  78             } else {
  79                 INSERT_WORDS(*iptr,i0,i1&(~i));
  80                 return x - *iptr;
  81             }
  82         }
  83 }