float_t, double_t − most efficient floating types
Math library (libm)
#include <math.h>
typedef
/* ... */ float_t;
typedef /* ... */ double_t;
The implementation’s most efficient floating types at least as wide as float and double respectively. Their type depends on the value of the macro FLT_EVAL_METHOD (defined in <float.h>):
For other values of FLT_EVAL_METHOD, the types of float_t and double_t are implementation-defined.
C11, POSIX.1-2008.
C99, POSIX.1-2001.
float.h(0p), math.h(0p)