lib/libm/src/s_scalbnl.c

   1 /*      $NetBSD: s_scalbnl.c,v 1.9 2013/05/20 19:40:09 joerg Exp $      */
   2
   3 /*-
   4  * Copyright (c) 2011 The NetBSD Foundation, Inc.
   5  * All rights reserved.
   6  *
   7  * This code is derived from software contributed to The NetBSD Foundation
   8  * by Joerg Sonnenberger.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
  20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
  23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  29  * POSSIBILITY OF SUCH DAMAGE.
  30  */
  31
  32 #include <sys/cdefs.h>
  33 __RCSID("$NetBSD: s_scalbnl.c,v 1.9 2013/05/20 19:40:09 joerg Exp $");
  34
  35 #include "namespace.h"
  36
  37 #include <float.h>
  38 #include <math.h>
  39 #include <machine/ieee.h>
  40
  41 #ifdef __HAVE_LONG_DOUBLE
  42
  43 #ifdef _LP64
  44 long double
  45 scalbnl(long double x, int n)
  46 {
  47         return scalblnl(x, n);
  48 }
  49 #else
  50 __strong_alias(_scalbnl, _scalblnl)
  51 #endif
  52
  53 __weak_alias(scalbnl, _scalbnl)
  54 __weak_alias(scalblnl, _scalblnl)
  55 __weak_alias(ldexpl, _scalbnl)
  56
  57 #if LDBL_MANT_DIG == 64
  58 #define FROM_UNDERFLOW  0x1p65L
  59 #define TO_UNDERFLOW    0x1p-65L
  60 #elif LDBL_MANT_DIG == 113
  61 #define FROM_UNDERFLOW  0x1p114L
  62 #define TO_UNDERFLOW    0x1p-114L
  63 #else
  64 #error Unsupported long double format
  65 #endif
  66
  67 long double
  68 scalblnl(long double x, long n)
  69 {
  70         union ieee_ext_u u;
  71
  72         /* Trivial cases first */
  73         if (n == 0 || x == 0.0L)
  74                 return x;
  75
  76         u.extu_ld = x;
  77
  78         /* NaN and infinite don't change either, but trigger exception */
  79         if (u.extu_ext.ext_exp == EXT_EXP_INFNAN)
  80                 return x + x;
  81
  82         /* Protect against integer overflow in calculation of new exponent */
  83         if (n > LDBL_MAX_EXP - LDBL_MIN_EXP + LDBL_MANT_DIG)
  84                 goto overflow;
  85         if (n < LDBL_MIN_EXP - LDBL_MAX_EXP - LDBL_MANT_DIG)
  86                 goto underflow;
  87
  88         /* Scale denormalized numbers slightly, so that they are normal */
  89         if (u.extu_ext.ext_exp == 0) {
  90                 u.extu_ld *= FROM_UNDERFLOW;
  91                 n -= LDBL_MANT_DIG + 1;
  92         }
  93
  94         n += u.extu_ext.ext_exp;
  95         if (n >= LDBL_MAX_EXP + EXT_EXP_BIAS)
  96                 goto overflow;
  97         /* Positive exponent (incl. bias) means normal result */
  98         if (n > 0) {
  99                 u.extu_ext.ext_exp = n;
 100                 return u.extu_ld;
 101         }
 102         /* Shift the exponent and let the multiply below handle subnormal */
 103         n += LDBL_MANT_DIG + 1;
 104         if (n <= 0)
 105                 goto underflow;
 106         u.extu_ext.ext_exp = n;
 107         return u.extu_ld * TO_UNDERFLOW;
 108
 109 underflow:
 110         return LDBL_MIN * copysignl(LDBL_MIN, x);
 111
 112 overflow:
 113         return LDBL_MAX * copysignl(LDBL_MAX, x);
 114 }
 115
 116 #endif