#include <math.h> double ldexp(double x, int exp); float ldexpf(float x, int exp); long double ldexpl(long double x, int exp);
These functions shall compute the quantity x * 2exp.
An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
If these functions would cause overflow, a range error shall occur and ldexp(), ldexpf(), and ldexpl() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (according to the sign of x), respectively.
If the correct value would cause underflow, and is not representable, a range error may occur, and ldexp(), ldexpf(), and ldexpl() shall return 0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
If x is NaN, a NaN shall be returned.
If x is ±0 or ±Inf, x shall be returned.
If exp is 0, x shall be returned.
If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.
These functions may fail if:
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.
The following sections are informative.
The Base Definitions volume of POSIX.1-2008, Section 4.19, Treatment of Error Conditions for Mathematical Functions, <math.h>
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