lib/isnan.c

   1 /* Test for NaN that does not need libm.
   2    Copyright (C) 2007-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
  18
  19 #include <config.h>
  20
  21 /* Specification.  */
  22 #ifdef USE_LONG_DOUBLE
  23 /* Specification found in math.h or isnanl-nolibm.h.  */
  24 extern int rpl_isnanl (long double x) _GL_ATTRIBUTE_CONST;
  25 #elif ! defined USE_FLOAT
  26 /* Specification found in math.h or isnand-nolibm.h.  */
  27 extern int rpl_isnand (double x);
  28 #else /* defined USE_FLOAT */
  29 /* Specification found in math.h or isnanf-nolibm.h.  */
  30 extern int rpl_isnanf (float x);
  31 #endif
  32
  33 #include <float.h>
  34 #include <string.h>
  35
  36 #include "float+.h"
  37
  38 #ifdef USE_LONG_DOUBLE
  39 # define FUNC rpl_isnanl
  40 # define DOUBLE long double
  41 # define MAX_EXP LDBL_MAX_EXP
  42 # define MIN_EXP LDBL_MIN_EXP
  43 # if defined LDBL_EXPBIT0_WORD && defined LDBL_EXPBIT0_BIT
  44 #  define KNOWN_EXPBIT0_LOCATION
  45 #  define EXPBIT0_WORD LDBL_EXPBIT0_WORD
  46 #  define EXPBIT0_BIT LDBL_EXPBIT0_BIT
  47 # endif
  48 # define SIZE SIZEOF_LDBL
  49 # define L_(literal) literal##L
  50 #elif ! defined USE_FLOAT
  51 # define FUNC rpl_isnand
  52 # define DOUBLE double
  53 # define MAX_EXP DBL_MAX_EXP
  54 # define MIN_EXP DBL_MIN_EXP
  55 # if defined DBL_EXPBIT0_WORD && defined DBL_EXPBIT0_BIT
  56 #  define KNOWN_EXPBIT0_LOCATION
  57 #  define EXPBIT0_WORD DBL_EXPBIT0_WORD
  58 #  define EXPBIT0_BIT DBL_EXPBIT0_BIT
  59 # endif
  60 # define SIZE SIZEOF_DBL
  61 # define L_(literal) literal
  62 #else /* defined USE_FLOAT */
  63 # define FUNC rpl_isnanf
  64 # define DOUBLE float
  65 # define MAX_EXP FLT_MAX_EXP
  66 # define MIN_EXP FLT_MIN_EXP
  67 # if defined FLT_EXPBIT0_WORD && defined FLT_EXPBIT0_BIT
  68 #  define KNOWN_EXPBIT0_LOCATION
  69 #  define EXPBIT0_WORD FLT_EXPBIT0_WORD
  70 #  define EXPBIT0_BIT FLT_EXPBIT0_BIT
  71 # endif
  72 # define SIZE SIZEOF_FLT
  73 # define L_(literal) literal##f
  74 #endif
  75
  76 #define EXP_MASK ((MAX_EXP - MIN_EXP) | 7)
  77
  78 #define NWORDS \
  79   ((sizeof (DOUBLE) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
  80 typedef union { DOUBLE value; unsigned int word[NWORDS]; } memory_double;
  81
  82 /* Most hosts nowadays use IEEE floating point, so they use IEC 60559
  83    representations, have infinities and NaNs, and do not trap on
  84    exceptions.  Define IEEE_FLOATING_POINT if this host is one of the
  85    typical ones.  The C23 macro __STDC_IEC_60559_BFP__ macro (or its cousin,
  86    the now-obsolescent C11 macro __STDC_IEC_559__) is close to what is
  87    wanted here, but is not quite right because this file does not require
  88    all the features of C23 Annex F (and works even with pre-C11 platforms,
  89    for that matter).  */
  90
  91 #define IEEE_FLOATING_POINT (FLT_RADIX == 2 && FLT_MANT_DIG == 24 \
  92                              && FLT_MIN_EXP == -125 && FLT_MAX_EXP == 128)
  93
  94 int
  95 FUNC (DOUBLE x)
  96 {
  97 #if defined KNOWN_EXPBIT0_LOCATION && IEEE_FLOATING_POINT
  98 # if defined USE_LONG_DOUBLE && ((defined __ia64 && LDBL_MANT_DIG == 64) || (defined __x86_64__ || defined __amd64__) || (defined __i386 || defined __i386__ || defined _I386 || defined _M_IX86 || defined _X86_)) && !HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
  99   /* Special CPU dependent code is needed to treat bit patterns outside the
 100      IEEE 754 specification (such as Pseudo-NaNs, Pseudo-Infinities,
 101      Pseudo-Zeroes, Unnormalized Numbers, and Pseudo-Denormals) as NaNs.
 102      These bit patterns are:
 103        - exponent = 0x0001..0x7FFF, mantissa bit 63 = 0,
 104        - exponent = 0x0000, mantissa bit 63 = 1.
 105      The NaN bit pattern is:
 106        - exponent = 0x7FFF, mantissa >= 0x8000000000000001.  */
 107   memory_double m;
 108   unsigned int exponent;
 109
 110   m.value = x;
 111   exponent = (m.word[EXPBIT0_WORD] >> EXPBIT0_BIT) & EXP_MASK;
 112 #  ifdef WORDS_BIGENDIAN
 113   /* Big endian: EXPBIT0_WORD = 0, EXPBIT0_BIT = 16.  */
 114   if (exponent == 0)
 115     return 1 & (m.word[0] >> 15);
 116   else if (exponent == EXP_MASK)
 117     return (((m.word[0] ^ 0x8000U) << 16) | m.word[1] | (m.word[2] >> 16)) != 0;
 118   else
 119     return 1 & ~(m.word[0] >> 15);
 120 #  else
 121   /* Little endian: EXPBIT0_WORD = 2, EXPBIT0_BIT = 0.  */
 122   if (exponent == 0)
 123     return (m.word[1] >> 31);
 124   else if (exponent == EXP_MASK)
 125     return ((m.word[1] ^ 0x80000000U) | m.word[0]) != 0;
 126   else
 127     return (m.word[1] >> 31) ^ 1;
 128 #  endif
 129 # else
 130   /* Be careful to not do any floating-point operation on x, such as x == x,
 131      because x may be a signaling NaN.  */
 132 #  if defined __SUNPRO_C || defined __ICC || defined _MSC_VER \
 133       || defined __DECC || defined __TINYC__ \
 134       || (defined __sgi && !defined __GNUC__)
 135   /* The Sun C 5.0, Intel ICC 10.0, Microsoft Visual C/C++ 9.0, Compaq (ex-DEC)
 136      6.4, and TinyCC compilers don't recognize the initializers as constant
 137      expressions.  The Compaq compiler also fails when constant-folding
 138      0.0 / 0.0 even when constant-folding is not required.  The Microsoft
 139      Visual C/C++ compiler also fails when constant-folding 1.0 / 0.0 even
 140      when constant-folding is not required. The SGI MIPSpro C compiler
 141      complains about "floating-point operation result is out of range".  */
 142   static DOUBLE zero = L_(0.0);
 143   memory_double nan;
 144   DOUBLE plus_inf = L_(1.0) / zero;
 145   DOUBLE minus_inf = -L_(1.0) / zero;
 146   nan.value = zero / zero;
 147 #  else
 148   static memory_double nan = { L_(0.0) / L_(0.0) };
 149   static DOUBLE plus_inf = L_(1.0) / L_(0.0);
 150   static DOUBLE minus_inf = -L_(1.0) / L_(0.0);
 151 #  endif
 152   {
 153     memory_double m;
 154
 155     /* A NaN can be recognized through its exponent.  But exclude +Infinity and
 156        -Infinity, which have the same exponent.  */
 157     m.value = x;
 158     if (((m.word[EXPBIT0_WORD] ^ nan.word[EXPBIT0_WORD])
 159          & (EXP_MASK << EXPBIT0_BIT))
 160         == 0)
 161       return (memcmp (&m.value, &plus_inf, SIZE) != 0
 162               && memcmp (&m.value, &minus_inf, SIZE) != 0);
 163     else
 164       return 0;
 165   }
 166 # endif
 167 #else
 168   /* The configuration did not find sufficient information, or does
 169      not use IEEE floating point.  Give up about the signaling NaNs;
 170      handle only the quiet NaNs.  */
 171   if (x == x)
 172     {
 173 # if defined USE_LONG_DOUBLE && ((defined __ia64 && LDBL_MANT_DIG == 64) || (defined __x86_64__ || defined __amd64__) || (defined __i386 || defined __i386__ || defined _I386 || defined _M_IX86 || defined _X86_)) && !HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
 174       /* Detect any special bit patterns that pass ==; see comment above.  */
 175       memory_double m1;
 176       memory_double m2;
 177
 178       memset (&m1.value, 0, SIZE);
 179       memset (&m2.value, 0, SIZE);
 180       m1.value = x;
 181       m2.value = x + (x ? 0.0L : -0.0L);
 182       if (memcmp (&m1.value, &m2.value, SIZE) != 0)
 183         return 1;
 184 # endif
 185       return 0;
 186     }
 187   else
 188     return 1;
 189 #endif
 190 }