#include <math.h>
double ldexp(double x, int exp);
ldexp multiplies a floating-point number by an integral power of 2.
ldexp returns x * 2^exp.
If the result overflows, errno is set to ERANGE and ldexp returns HUGE_VAL.
If x is ? or NaN, ldexp returns x.
If the result overflows, ldexp returns ?.
ldexp conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).