newlib/libm/common/s_trunc.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 FUNCTION
  13 <<trunc>>, <<truncf>>---round to integer, towards zero
  14 INDEX
  15         trunc
  16 INDEX
  17         truncf
  18
  19 SYNOPSIS
  20         #include <math.h>
  21         double trunc(double <[x]>);
  22         float truncf(float <[x]>);
  23
  24 DESCRIPTION
  25         The <<trunc>> functions round their argument to the integer value, in
  26         floating format, nearest to but no larger in magnitude than the
  27         argument, regardless of the current rounding direction.  (While the
  28         "inexact" floating-point exception behavior is unspecified by the C
  29         standard, the <<trunc>> functions are written so that "inexact" is not
  30         raised if the result does not equal the argument, which behavior is as
  31         recommended by IEEE 754 for its related functions.)
  32
  33 RETURNS
  34 <[x]> truncated to an integral value.
  35
  36 PORTABILITY
  37 ANSI C, POSIX
  38
  39 */
  40
  41 #include "fdlibm.h"
  42
  43 #ifndef _DOUBLE_IS_32BITS
  44
  45 #ifdef __STDC__
  46         double trunc(double x)
  47 #else
  48         double trunc(x)
  49         double x;
  50 #endif
  51 {
  52   int signbit;
  53   /* Most significant word, least significant word. */
  54   int msw;
  55   unsigned int lsw;
  56   int exponent_less_1023;
  57
  58   EXTRACT_WORDS(msw, lsw, x);
  59
  60   /* Extract sign bit. */
  61   signbit = msw & 0x80000000;
  62
  63   /* Extract exponent field. */
  64   exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;
  65
  66   if (exponent_less_1023 < 20)
  67     {
  68       /* All significant digits are in msw. */
  69       if (exponent_less_1023 < 0)
  70         {
  71           /* -1 < x < 1, so result is +0 or -0. */
  72           INSERT_WORDS(x, signbit, 0);
  73         }
  74       else
  75         {
  76           /* All relevant fraction bits are in msw, so lsw of the result is 0. */
  77           INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 0);
  78         }
  79     }
  80   else if (exponent_less_1023 > 51)
  81     {
  82       if (exponent_less_1023 == 1024)
  83         {
  84           /* x is infinite, or not a number, so trigger an exception. */
  85           return x + x;
  86         }
  87       /* All bits in the fraction fields of the msw and lsw are needed in the result. */
  88     }
  89   else
  90     {
  91       /* All fraction bits in msw are relevant.  Truncate irrelevant
  92          bits from lsw. */
  93       INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20)));
  94     }
  95   return x;
  96 }
  97
  98 #endif /* _DOUBLE_IS_32BITS */