lib/libm/src/lrint.c

   1 /*-
   2  * Copyright (c) 2004
   3  *      Matthias Drochner. All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $NetBSD: lrint.c,v 1.3 2004/10/13 15:18:32 drochner Exp $
  27  * $DragonFly: src/lib/libm/src/lrint.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  28  */
  29
  30 #include <math.h>
  31 #include <sys/ieee754.h>
  32 #include <machine/limits.h>
  33 #include "math_private.h"
  34
  35 #ifndef LRINTNAME
  36 #define LRINTNAME lrint
  37 #define RESTYPE long int
  38 #define RESTYPE_MIN LONG_MIN
  39 #define RESTYPE_MAX LONG_MAX
  40 #endif
  41
  42 #define RESTYPE_BITS (sizeof(RESTYPE) * 8)
  43
  44 static const double
  45 TWO52[2]={
  46   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  47  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  48 };
  49
  50 RESTYPE
  51 LRINTNAME(double x)
  52 {
  53         u_int32_t i0, i1;
  54         int e, s, shift;
  55         RESTYPE res;
  56
  57         GET_HIGH_WORD(i0, x);
  58         e = i0 >> 20;
  59         s = e >> DBL_EXPBITS;
  60         e = (e & 0x7ff) - DBL_EXP_BIAS;
  61
  62         /* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
  63         if (e < -1)
  64                 return (0);
  65         /* 1.0 x 2^31 (or 2^63) is already too large */
  66         if (e >= (int)RESTYPE_BITS - 1)
  67                 return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */
  68
  69         /* >= 2^52 is already an exact integer */
  70         if (e < DBL_FRACBITS) {
  71                 /* round, using current direction */
  72                 x += TWO52[s];
  73                 x -= TWO52[s];
  74         }
  75
  76         EXTRACT_WORDS(i0, i1, x);
  77         e = ((i0 >> 20) & 0x7ff) - DBL_EXP_BIAS;
  78         i0 &= 0xfffff;
  79         i0 |= (1 << 20);
  80
  81         shift = e - DBL_FRACBITS;
  82         if (shift >=0)
  83                 res = (shift < 32 ? (RESTYPE)i1 << shift : 0);
  84         else
  85                 res = (shift > -32 ? i1 >> -shift : 0);
  86         shift += 32;
  87         if (shift >=0)
  88                 res |= (shift < 32 ? (RESTYPE)i0 << shift : 0);
  89         else
  90                 res |= (shift > -32 ? i0 >> -shift : 0);
  91
  92         return (s ? -res : res);
  93 }