FLT_EVAL_METHOD

From cppreference.com
< c‎ | types‎ | limits
Defined in header <float.h>
#define FLT_EVAL_METHOD /* implementation defined */
(since C99)

Specifies range and precision of floating-point values obtained from floating-point constants and from all operations (operators, implicit conversions of operands) except assignment, cast, and library function call.

Value Explanation
negative values except -1 implementation-defined behavior
-1 the default precision is not known
0 all operations and constants evaluate in the range and precision of the type used. Additionally, float_t and double_t are equivalent to float and double respectively
1 all operations and constants evaluate in the range and precision of double. Additionally, both float_t and double_t are equivalent to double
2 all operations and constants evaluate in the range and precision of long double. Additionally, both float_t and double_t are equivalent to long double

Notes

Regardless of the value of FLT_EVAL_METHOD, any floating-point expression may be contracted, that is, calculated as if all intermediate results have infinite range and precision (unless #pragma STDC FP_CONTRACT is off)

Cast and assignment strip away any extraneous range and precision: this models the action of storing a value from an extended-precision FPU register into a standard-sized memory location.

See also

most efficient floating-point type at least as wide as float or double
(typedef)