lib/libm/src/lround.c

   1 /* $NetBSD: lround.c,v 1.3 2008/04/26 23:49:50 christos Exp $ */
   2
   3 /*-
   4  * Copyright (c) 2004
   5  *      Matthias Drochner. All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  */
  28
  29 #include <math.h>
  30 #include <sys/ieee754.h>
  31 #include <machine/limits.h>
  32 #include "math_private.h"
  33
  34 #ifndef LROUNDNAME
  35 #define LROUNDNAME lround
  36 #define RESTYPE long int
  37 #define RESTYPE_MIN LONG_MIN
  38 #define RESTYPE_MAX LONG_MAX
  39 #endif
  40
  41 #define RESTYPE_BITS (sizeof(RESTYPE) * 8)
  42
  43 RESTYPE
  44 LROUNDNAME(double x)
  45 {
  46         u_int32_t i0, i1;
  47         int e, s, shift;
  48         RESTYPE res;
  49
  50         GET_HIGH_WORD(i0, x);
  51         e = i0 >> 20;
  52         s = (uint32_t)e >> DBL_EXPBITS;
  53         e = (e & 0x7ff) - DBL_EXP_BIAS;
  54
  55         /* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
  56         if (e < -1)
  57                 return (0);
  58         /* 1.0 x 2^31 (or 2^63) is already too large */
  59         if (e >= (int)RESTYPE_BITS - 1)
  60                 return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */
  61
  62         /* >= 2^52 is already an exact integer */
  63         if (e < DBL_FRACBITS) {
  64                 /* add 0.5, extraction below will truncate */
  65                 x += (s ? -0.5 : 0.5);
  66         }
  67
  68         EXTRACT_WORDS(i0, i1, x);
  69         e = ((i0 >> 20) & 0x7ff) - DBL_EXP_BIAS;
  70         i0 &= 0xfffff;
  71         i0 |= (1 << 20);
  72
  73         shift = e - DBL_FRACBITS;
  74         if (shift >=0)
  75                 res = (shift < 32 ? (RESTYPE)i1 << shift : 0);
  76         else
  77                 res = (shift > -32 ? i1 >> -shift : 0);
  78         shift += 32;
  79         if (shift >=0)
  80                 res |= (shift < 32 ? (RESTYPE)i0 << shift : 0);
  81         else
  82                 res |= (shift > -32 ? i0 >> -shift : 0);
  83
  84         return (s ? -res : res);
  85 }