newlib/libm/ld/s_rintl.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   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 __FBSDID("$FreeBSD$");
  31
  32 #include <float.h>
  33 #include <math.h>
  34 #include <stdint.h>
  35
  36 #include "fpmath.h"
  37
  38 #if LDBL_MAX_EXP != 0x4000
  39 /* We also require the usual bias, min exp and expsign packing. */
  40 #error "Unsupported long double format"
  41 #endif
  42
  43 #define BIAS    (LDBL_MAX_EXP - 1)
  44
  45 static const float
  46 shift[2] = {
  47 #if LDBL_MANT_DIG == 64
  48         0x1.0p63, -0x1.0p63
  49 #elif LDBL_MANT_DIG == 113
  50         0x1.0p112, -0x1.0p112
  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 IEEEl2bits u;
  61         uint32_t expsign;
  62         int ex, sign;
  63
  64         u.e = x;
  65         expsign = u.xbits.expsign;
  66         ex = expsign & 0x7fff;
  67
  68         if (ex >= BIAS + LDBL_MANT_DIG - 1) {
  69                 if (ex == BIAS + LDBL_MAX_EXP)
  70                         return (x + x); /* Inf, NaN, or unsupported format */
  71                 return (x);             /* finite and already an integer */
  72         }
  73         sign = expsign >> 15;
  74
  75         /*
  76          * The following code assumes that intermediate results are
  77          * evaluated in long double precision. If they are evaluated in
  78          * greater precision, double rounding may occur, and if they are
  79          * evaluated in less precision (as on i386), results will be
  80          * wildly incorrect.
  81          */
  82         x += shift[sign];
  83         x -= shift[sign];
  84
  85         /*
  86          * If the result is +-0, then it must have the same sign as x, but
  87          * the above calculation doesn't always give this.  Fix up the sign.
  88          */
  89         if (ex < BIAS && x == 0.0L)
  90                 return (zero[sign]);
  91
  92         return (x);
  93 }