contrib/openbsd_libm/src/s_rintl.c

   1 /*      $OpenBSD: s_rintl.c,v 1.1 2008/12/09 20:00:35 martynas Exp $    */
   2 /*-
   3  * Copyright (c) 2008 David Schultz <das@FreeBSD.ORG>
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  25  * SUCH DAMAGE.
  26  */
  27
  28 #include <sys/types.h>
  29 #include <machine/ieee.h>
  30 #include <float.h>
  31 #include <math.h>
  32
  33 #if LDBL_MAX_EXP != 0x4000
  34 /* We also require the usual bias, min exp and expsign packing. */
  35 #error "Unsupported long double format"
  36 #endif
  37
  38 #define BIAS    (LDBL_MAX_EXP - 1)
  39
  40 static const float
  41 shift[2] = {
  42 #if LDBL_MANT_DIG == 64
  43         0x1.0p63, -0x1.0p63
  44 #elif LDBL_MANT_DIG == 113
  45         0x1.0p112, -0x1.0p112
  46 #else
  47 #error "Unsupported long double format"
  48 #endif
  49 };
  50 static const float zero[2] = { 0.0, -0.0 };
  51
  52 long double
  53 rintl(long double x)
  54 {
  55         union {
  56                 long double e;
  57                 struct ieee_ext bits;
  58         } u;
  59         uint32_t expsign;
  60         int ex, sign;
  61
  62         u.e = x;
  63         expsign = (u.bits.ext_sign << 15) | u.bits.ext_exp;
  64         ex = expsign & 0x7fff;
  65
  66         if (ex >= BIAS + LDBL_MANT_DIG - 1) {
  67                 if (ex == BIAS + LDBL_MAX_EXP)
  68                         return (x + x); /* Inf, NaN, or unsupported format */
  69                 return (x);             /* finite and already an integer */
  70         }
  71         sign = expsign >> 15;
  72
  73         /*
  74          * The following code assumes that intermediate results are
  75          * evaluated in long double precision. If they are evaluated in
  76          * greater precision, double rounding may occur, and if they are
  77          * evaluated in less precision (as on i386), results will be
  78          * wildly incorrect.
  79          */
  80         x += shift[sign];
  81         x -= shift[sign];
  82
  83         /*
  84          * If the result is +-0, then it must have the same sign as x, but
  85          * the above calculation doesn't always give this.  Fix up the sign.
  86          */
  87         if (ex < BIAS && x == 0.0L)
  88                 return (zero[sign]);
  89
  90         return (x);
  91 }