lib/libm/src/lrint.c

   1 /* $NetBSD: lrint.c,v 1.4 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 LRINTNAME
  35 #define LRINTNAME lrint
  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 static const double
  44 TWO52[2]={
  45   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  46  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  47 };
  48
  49 RESTYPE
  50 LRINTNAME(double x)
  51 {
  52         u_int32_t i0, i1;
  53         int e, s, shift;
  54         RESTYPE res;
  55
  56         GET_HIGH_WORD(i0, x);
  57         e = i0 >> 20;
  58         s = (uint32_t)e >> DBL_EXPBITS;
  59         e = (e & 0x7ff) - DBL_EXP_BIAS;
  60
  61         /* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
  62         if (e < -1)
  63                 return (0);
  64         /* 1.0 x 2^31 (or 2^63) is already too large */
  65         if (e >= (int)RESTYPE_BITS - 1)
  66                 return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */
  67
  68         /* >= 2^52 is already an exact integer */
  69         if (e < DBL_FRACBITS) {
  70                 /* round, using current direction */
  71                 x += TWO52[s];
  72                 x -= TWO52[s];
  73         }
  74
  75         EXTRACT_WORDS(i0, i1, x);
  76         e = ((i0 >> 20) & 0x7ff) - DBL_EXP_BIAS;
  77         i0 &= 0xfffff;
  78         i0 |= (1 << 20);
  79
  80         shift = e - DBL_FRACBITS;
  81         if (shift >=0)
  82                 res = (shift < 32 ? (RESTYPE)i1 << shift : 0);
  83         else
  84                 res = (shift > -32 ? i1 >> -shift : 0);
  85         shift += 32;
  86         if (shift >=0)
  87                 res |= (shift < 32 ? (RESTYPE)i0 << shift : 0);
  88         else
  89                 res |= (shift > -32 ? i0 >> -shift : 0);
  90
  91         return (s ? -res : res);
  92 }