+ return 1 & ~(m.word[0] >> 15);
+# else
+ /* Little endian: EXPBIT0_WORD = 2, EXPBIT0_BIT = 0. */
+ if (exponent == 0)
+ return (m.word[1] >> 31);
+ else if (exponent == EXP_MASK)
+ return ((m.word[1] ^ 0x80000000U) | m.word[0]) != 0;
+ else
+ return (m.word[1] >> 31) ^ 1;
+# endif
+# else
+ /* Be careful to not do any floating-point operation on x, such as x == x,
+ because x may be a signaling NaN. */
+# if defined __SUNPRO_C || defined __DECC || (defined __sgi && !defined __GNUC__)
+ /* The Sun C 5.0 compilers and the Compaq (ex-DEC) 6.4 compilers don't
+ recognize the initializers as constant expressions. The latter compiler
+ also fails when constant-folding 0.0 / 0.0 even when constant-folding is
+ not required. The SGI MIPSpro C compiler complains about "floating-point
+ operation result is out of range". */
+ static DOUBLE zero = L_(0.0);
+ memory_double nan;
+ DOUBLE plus_inf = L_(1.0) / L_(0.0);
+ DOUBLE minus_inf = -L_(1.0) / L_(0.0);
+ nan.value = zero / zero;
+# else
+ static memory_double nan = { L_(0.0) / L_(0.0) };
+ static DOUBLE plus_inf = L_(1.0) / L_(0.0);
+ static DOUBLE minus_inf = -L_(1.0) / L_(0.0);
+# endif
+ {
+ memory_double m;
+
+ /* A NaN can be recognized through its exponent. But exclude +Infinity and
+ -Infinity, which have the same exponent. */
+ m.value = x;
+ if (((m.word[EXPBIT0_WORD] ^ nan.word[EXPBIT0_WORD])
+ & (EXP_MASK << EXPBIT0_BIT))
+ == 0)
+ return (memcmp (&m.value, &plus_inf, SIZE) != 0
+ && memcmp (&m.value, &minus_inf, SIZE) != 0);
+ else
+ return 0;
+ }
+# endif