newlib/libm/common/s_lround.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 <<lround>>, <<lroundf>>, <<llround>>, <<llroundf>>---round to integer, to nearest
  14 INDEX
  15         lround
  16 INDEX
  17         lroundf
  18 INDEX
  19         llround
  20 INDEX
  21         llroundf
  22
  23 SYNOPSIS
  24         #include <math.h>
  25         long int lround(double <[x]>);
  26         long int lroundf(float <[x]>);
  27         long long int llround(double <[x]>);
  28         long long int llroundf(float <[x]>);
  29
  30 DESCRIPTION
  31         The <<lround>> and <<llround>> functions round their argument to the
  32         nearest integer value, rounding halfway cases away from zero, regardless
  33         of the current rounding direction.  If the rounded value is outside the
  34         range of the return type, the numeric result is unspecified (depending
  35         upon the floating-point implementation, not the library).  A range
  36         error may occur if the magnitude of x is too large.
  37
  38 RETURNS
  39 <[x]> rounded to an integral value as an integer.
  40
  41 SEEALSO
  42 See the <<round>> functions for the return being the same floating-point type
  43 as the argument.  <<lrint>>, <<llrint>>.
  44
  45 PORTABILITY
  46 ANSI C, POSIX
  47
  48 */
  49
  50 #include "fdlibm.h"
  51
  52 #ifndef _DOUBLE_IS_32BITS
  53
  54 #ifdef __STDC__
  55         long int lround(double x)
  56 #else
  57         long int lround(x)
  58         double x;
  59 #endif
  60 {
  61   __int32_t sign, exponent_less_1023;
  62   /* Most significant word, least significant word. */
  63   __uint32_t msw, lsw;
  64   long int result;
  65
  66   EXTRACT_WORDS(msw, lsw, x);
  67
  68   /* Extract sign. */
  69   sign = ((msw & 0x80000000) ? -1 : 1);
  70   /* Extract exponent field. */
  71   exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;
  72   msw &= 0x000fffff;
  73   msw |= 0x00100000;
  74   /* exponent_less_1023 in [-1023,1024] */
  75   if (exponent_less_1023 < 20)
  76     {
  77       /* exponent_less_1023 in [-1023,19] */
  78       if (exponent_less_1023 < 0)
  79         {
  80           if (exponent_less_1023 < -1)
  81             return 0;
  82           else
  83             return sign;
  84         }
  85       else
  86         {
  87           /* exponent_less_1023 in [0,19] */
  88           /* shift amt in [0,19] */
  89           msw += 0x80000 >> exponent_less_1023;
  90           /* shift amt in [20,1] */
  91           result = msw >> (20 - exponent_less_1023);
  92         }
  93     }
  94   else if (exponent_less_1023 < (8 * sizeof (long int)) - 1)
  95     {
  96       /* 32bit long: exponent_less_1023 in [20,30] */
  97       /* 64bit long: exponent_less_1023 in [20,62] */
  98       if (exponent_less_1023 >= 52)
  99         /* 64bit long: exponent_less_1023 in [52,62] */
 100         /* 64bit long: shift amt in [32,42] */
 101         result = ((long int) msw << (exponent_less_1023 - 20))
 102                 /* 64bit long: shift amt in [0,10] */
 103                 | (lsw << (exponent_less_1023 - 52));
 104       else
 105         {
 106           /* 32bit long: exponent_less_1023 in [20,30] */
 107           /* 64bit long: exponent_less_1023 in [20,51] */
 108           unsigned int tmp = lsw
 109                     /* 32bit long: shift amt in [0,10] */
 110                     /* 64bit long: shift amt in [0,31] */
 111                     + (0x80000000 >> (exponent_less_1023 - 20));
 112           if (tmp < lsw)
 113             ++msw;
 114           /* 32bit long: shift amt in [0,10] */
 115           /* 64bit long: shift amt in [0,31] */
 116           result = ((long int) msw << (exponent_less_1023 - 20))
 117                     /* ***32bit long: shift amt in [32,22] */
 118                     /* ***64bit long: shift amt in [32,1] */
 119                     | SAFE_RIGHT_SHIFT (tmp, (52 - exponent_less_1023));
 120         }
 121     }
 122   else
 123     /* Result is too large to be represented by a long int. */
 124     return (long int)x;
 125
 126   return sign * result;
 127 }
 128
 129 #endif /* _DOUBLE_IS_32BITS */