lib/libm/src/s_rintl.c

   1 /*      $NetBSD: s_rintl.c,v 1.5 2013/08/21 13:04:44 martin Exp $       */
   2
   3 /*-
   4  * Copyright (c) 2008 David Schultz <das@FreeBSD.ORG>
   5  * 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 <sys/cdefs.h>
  30 #if 0
  31 __FBSDID("$FreeBSD: src/lib/msun/src/s_rintl.c,v 1.5 2008/02/22 11:59:05 bde Exp $");
  32 #else
  33 __RCSID("$NetBSD: s_rintl.c,v 1.5 2013/08/21 13:04:44 martin Exp $");
  34 #endif
  35
  36 #include <float.h>
  37 #include <machine/ieee.h>
  38
  39 #include "math.h"
  40 #include "math_private.h"
  41
  42 #ifdef __HAVE_LONG_DOUBLE
  43 static const float
  44 shift[2] = {
  45 #if EXT_FRACBITS == 64
  46         0x1.0p63, -0x1.0p63
  47 #elif EXT_FRACBITS == 113
  48         0x1.0p112, -0x1.0p112
  49 #elif EXT_FRACBITS == 112
  50         0x1.0p111, -0x1.0p111
  51 #else
  52 #error "Unsupported long double format"
  53 #endif
  54 };
  55 static const float zero[2] = { 0.0, -0.0 };
  56
  57 long double
  58 rintl(long double x)
  59 {
  60         union ieee_ext_u u;
  61         uint32_t expsign;
  62         int ex, sign;
  63
  64         u.extu_ld = x;
  65         u.extu_ext.ext_frach &= ~0x80000000;
  66         expsign = u.extu_ext.ext_sign;
  67         ex = expsign & 0x7fff;
  68
  69         if (ex >= EXT_EXP_BIAS + EXT_FRACBITS - 1) {
  70                 if (ex == EXT_EXP_BIAS + EXT_FRACBITS)
  71                         return (x + x); /* Inf, NaN, or unsupported format */
  72                 return (x);             /* finite and already an integer */
  73         }
  74         sign = expsign >> 15;
  75
  76         /*
  77          * The following code assumes that intermediate results are
  78          * evaluated in long double precision. If they are evaluated in
  79          * greater precision, double rounding may occur, and if they are
  80          * evaluated in less precision (as on i386), results will be
  81          * wildly incorrect.
  82          */
  83         x += shift[sign];
  84         x -= shift[sign];
  85
  86         /*
  87          * If the result is +-0, then it must have the same sign as x, but
  88          * the above calculation doesn't always give this.  Fix up the sign.
  89          */
  90         if (ex < EXT_EXP_BIAS && x == 0.0L)
  91                 return (zero[sign]);
  92
  93         return (x);
  94 }
  95 #endif