newlib/libm/common/s_modf.c

   1
   2 /* @(#)s_modf.c 5.1 93/09/24 */
   3 /*
   4  * ====================================================
   5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   6  *
   7  * Developed at SunPro, a Sun Microsystems, Inc. business.
   8  * Permission to use, copy, modify, and distribute this
   9  * software is freely granted, provided that this notice
  10  * is preserved.
  11  * ====================================================
  12  */
  13
  14 /*
  15 FUNCTION
  16        <<modf>>, <<modff>>---split fractional and integer parts
  17
  18 INDEX
  19         modf
  20 INDEX
  21         modff
  22
  23 SYNOPSIS
  24         #include <math.h>
  25         double modf(double <[val]>, double *<[ipart]>);
  26         float modff(float <[val]>, float *<[ipart]>);
  27
  28 DESCRIPTION
  29         <<modf>> splits the double <[val]> apart into an integer part
  30         and a fractional part, returning the fractional part and
  31         storing the integer part in <<*<[ipart]>>>.  No rounding
  32         whatsoever is done; the sum of the integer and fractional
  33         parts is guaranteed to be exactly  equal to <[val]>.   That
  34         is, if <[realpart]> = modf(<[val]>, &<[intpart]>); then
  35         `<<<[realpart]>+<[intpart]>>>' is the same as <[val]>.
  36         <<modff>> is identical, save that it takes and returns
  37         <<float>> rather than <<double>> values.
  38
  39 RETURNS
  40         The fractional part is returned.  Each result has the same
  41         sign as the supplied argument <[val]>.
  42
  43 PORTABILITY
  44         <<modf>> is ANSI C. <<modff>> is an extension.
  45
  46 QUICKREF
  47         modf  ansi pure
  48         modff - pure
  49
  50 */
  51
  52 /*
  53  * modf(double x, double *iptr)
  54  * return fraction part of x, and return x's integral part in *iptr.
  55  * Method:
  56  *      Bit twiddling.
  57  *
  58  * Exception:
  59  *      No exception.
  60  */
  61
  62 #include "fdlibm.h"
  63
  64 #ifndef _DOUBLE_IS_32BITS
  65
  66 #ifdef __STDC__
  67         double modf(double x, double *iptr)
  68 #else
  69         double modf(x, iptr)
  70         double x,*iptr;
  71 #endif
  72 {
  73         __int32_t i0,i1,j0;
  74         __uint32_t i;
  75         EXTRACT_WORDS(i0,i1,x);
  76         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  77         if(j0<20) {                     /* integer part in high x */
  78             if(j0<0) {                  /* |x|<1 */
  79                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  80                 return x;
  81             } else {
  82                 i = (0x000fffff)>>j0;
  83                 if(((i0&i)|i1)==0) {            /* x is integral */
  84                     *iptr = x;
  85                     INSERT_WORDS(x,i0&0x80000000,0);    /* return +-0 */
  86                     return x;
  87                 } else {
  88                     INSERT_WORDS(*iptr,i0&(~i),0);
  89                     return x - *iptr;
  90                 }
  91             }
  92         } else if (j0>51) {             /* no fraction part */
  93             *iptr = x;
  94             if (__fpclassifyd(x) == FP_NAN) return *iptr = x+x; /* x is NaN, return NaN */
  95             INSERT_WORDS(x,i0&0x80000000,0);    /* return +-0 */
  96             return x;
  97         } else {                        /* fraction part in low x */
  98             i = ((__uint32_t)(0xffffffff))>>(j0-20);
  99             if((i1&i)==0) {             /* x is integral */
 100                 *iptr = x;
 101                 INSERT_WORDS(x,i0&0x80000000,0);        /* return +-0 */
 102                 return x;
 103             } else {
 104                 INSERT_WORDS(*iptr,i0,i1&(~i));
 105                 return x - *iptr;
 106             }
 107         }
 108 }
 109
 110 #endif /* _DOUBLE_IS_32BITS */