lib/libm/src/lrintf.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: lrintf.c,v 1.4 2006/08/01 20:14:35 drochner Exp $
  27  * $DragonFly: src/lib/libm/src/lrintf.c,v 1.2 2007/06/17 02:27:53 pavalos 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 lrintf
  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 float
  45 TWO23[2]={
  46   8.3886080000e+06, /* 0x4b000000 */
  47  -8.3886080000e+06, /* 0xcb000000 */
  48 };
  49
  50 RESTYPE
  51 LRINTNAME(float x)
  52 {
  53         u_int32_t i0;
  54         int e, s, shift;
  55         RESTYPE res;
  56 #ifdef __i386__ /* XXX gcc4 will omit the rounding otherwise */
  57         volatile
  58 #endif
  59                 float w;
  60
  61         GET_FLOAT_WORD(i0, x);
  62         e = i0 >> SNG_FRACBITS;
  63         s = e >> SNG_EXPBITS;
  64         e = (e & 0xff) - SNG_EXP_BIAS;
  65
  66         /* 1.0 x 2^-1 is the smallest number which can be rounded to 1 */
  67         if (e < -1)
  68                 return (0);
  69         /* 1.0 x 2^31 (or 2^63) is already too large */
  70         if (e >= (int)RESTYPE_BITS - 1)
  71                 return (s ? RESTYPE_MIN : RESTYPE_MAX); /* ??? unspecified */
  72
  73         /* >= 2^23 is already an exact integer */
  74         if (e < SNG_FRACBITS) {
  75                 /* round, using current direction */
  76                 w = TWO23[s] + x;
  77                 x = w - TWO23[s];
  78         }
  79
  80         GET_FLOAT_WORD(i0, x);
  81         e = ((i0 >> SNG_FRACBITS) & 0xff) - SNG_EXP_BIAS;
  82         i0 &= 0x7fffff;
  83         i0 |= (1 << SNG_FRACBITS);
  84
  85         shift = e - SNG_FRACBITS;
  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 }