Floating-Point Format Builtins (Using the GNU Compiler Collection (GCC))

7.2.1 Floating-Point Format Builtins

Built-in Function: double __builtin_huge_val (void): Returns a positive infinity, if supported by the floating-point format, else DBL_MAX. This function is suitable for implementing the ISO C macro HUGE_VAL.

Built-in Function: float __builtin_huge_valf (void): Similar to __builtin_huge_val, except the return type is float.

Built-in Function: long double __builtin_huge_vall (void): Similar to __builtin_huge_val, except the return type is long double.

Built-in Function: _Floatn __builtin_huge_valfn (void): Similar to __builtin_huge_val, except the return type is _Floatn.

Built-in Function: _Floatnx __builtin_huge_valfnx (void): Similar to __builtin_huge_val, except the return type is _Floatnx.

Built-in Function: int __builtin_fpclassify (int, int, int, int, int, ...): This built-in implements the C99 fpclassify functionality. The first five int arguments should be the target library’s notion of the possible FP classes and are used for return values. They must be constant values and they must appear in this order: FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL and FP_ZERO. The ellipsis is for exactly one floating-point value to classify. GCC treats the last argument as type-generic, which means it does not do default promotion from float to double.

Built-in Function: double __builtin_inf (void): Similar to __builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.

Built-in Function: _Decimal32 __builtin_infd32 (void): Similar to __builtin_inf, except the return type is _Decimal32.

Built-in Function: _Decimal64 __builtin_infd64 (void): Similar to __builtin_inf, except the return type is _Decimal64.

Built-in Function: _Decimal128 __builtin_infd128 (void): Similar to __builtin_inf, except the return type is _Decimal128.

Built-in Function: float __builtin_inff (void): Similar to __builtin_inf, except the return type is float. This function is suitable for implementing the ISO C99 macro INFINITY.

Built-in Function: long double __builtin_infl (void): Similar to __builtin_inf, except the return type is long double.

Built-in Function: _Floatn __builtin_inffn (void): Similar to __builtin_inf, except the return type is _Floatn.

Built-in Function: _Floatn __builtin_inffnx (void): Similar to __builtin_inf, except the return type is _Floatnx.

Built-in Function: int __builtin_isinf_sign (...): Similar to isinf, except the return value is -1 for an argument of -Inf and 1 for an argument of +Inf. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double.

Built-in Function: double __builtin_nan (const char *str)

This is an implementation of the ISO C99 function nan.

Since ISO C99 defines this function in terms of strtod, which we do not implement, a description of the parsing is in order. The string is parsed as by strtol; that is, the base is recognized by leading ‘0’ or ‘0x’ prefixes. The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand. The number is truncated to fit the significand field provided. The significand is forced to be a quiet NaN.

This function, if given a string literal all of which would have been consumed by strtol, is evaluated early enough that it is considered a compile-time constant.

Built-in Function: _Decimal32 __builtin_nand32 (const char *str): Similar to __builtin_nan, except the return type is _Decimal32.

Built-in Function: _Decimal64 __builtin_nand64 (const char *str): Similar to __builtin_nan, except the return type is _Decimal64.

Built-in Function: _Decimal128 __builtin_nand128 (const char *str): Similar to __builtin_nan, except the return type is _Decimal128.

Built-in Function: float __builtin_nanf (const char *str): Similar to __builtin_nan, except the return type is float.

Built-in Function: long double __builtin_nanl (const char *str): Similar to __builtin_nan, except the return type is long double.

Built-in Function: _Floatn __builtin_nanfn (const char *str): Similar to __builtin_nan, except the return type is _Floatn.

Built-in Function: _Floatnx __builtin_nanfnx (const char *str): Similar to __builtin_nan, except the return type is _Floatnx.

Built-in Function: double __builtin_nans (const char *str): Similar to __builtin_nan, except the significand is forced to be a signaling NaN. The nans function is proposed by WG14 N965.

Built-in Function: _Decimal32 __builtin_nansd32 (const char *str): Similar to __builtin_nans, except the return type is _Decimal32.

Built-in Function: _Decimal64 __builtin_nansd64 (const char *str): Similar to __builtin_nans, except the return type is _Decimal64.

Built-in Function: _Decimal128 __builtin_nansd128 (const char *str): Similar to __builtin_nans, except the return type is _Decimal128.

Built-in Function: float __builtin_nansf (const char *str): Similar to __builtin_nans, except the return type is float.

Built-in Function: long double __builtin_nansl (const char *str): Similar to __builtin_nans, except the return type is long double.

Built-in Function: _Floatn __builtin_nansfn (const char *str): Similar to __builtin_nans, except the return type is _Floatn.

Built-in Function: _Floatnx __builtin_nansfnx (const char *str): Similar to __builtin_nans, except the return type is _Floatnx.

Built-in Function: int __builtin_issignaling (...): Return non-zero if the argument is a signaling NaN and zero otherwise. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double. This built-in function can work even without the non-default -fsignaling-nans option, although if a signaling NaN is computed, stored or passed as argument to some function other than this built-in in the current translation unit, it is safer to use -fsignaling-nans. With -ffinite-math-only option this built-in function will always return 0.

Built-in Function: double __builtin_powi (double, int)
Built-in Function: float __builtin_powif (float, int)
Built-in Function: long double __builtin_powil (long double, int): Returns the first argument raised to the power of the second. Unlike the pow function no guarantees about precision and rounding are made.