ldexp, ldexpf, ldexpl

Multiplies a floating-point number by an integral power of two.

Syntax

double ldexp(
   double x,
   int exp
);
float ldexpf(
   float x,
   int exp
);
long double ldexpl(
   long double x,
   int exp
);
#define ldexp(X, INT) // Requires C11 or later

float ldexp(
   float x,
   int exp
);  // C++ only
long double ldexp(
   long double x,
   int exp
);  // C++ only

Parameters

x
Floating-point value.

exp
Integer exponent.

Return value

The ldexp functions return the value of x * 2^exp if successful. On overflow, and depending on the sign of x, ldexp returns +/- HUGE_VAL; the errno value is set to ERANGE.

For more information about errno and possible error return values, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Remarks

Because C++ allows overloading, you can call overloads of ldexp that take float or long double types. In a C program, unless you're using the <tgmath.h> macro to call this function, ldexp always takes a double and an int and returns a double.

If you use the <tgmath.h> ldexp() macro, the type of the argument determines which version of the function is selected. See Type-generic math for details.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

For compatibility information, see Compatibility.

Example

// crt_ldexp.c

#include <math.h>
#include <stdio.h>

int main( void )
{
   double x = 4.0, y;
   int p = 3;

   y = ldexp( x, p );
   printf( "%2.1f times two to the power of %d is %2.1f\n", x, p, y );
}

Output

4.0 times two to the power of 3 is 32.0

See also

Math and floating-point support
frexp
modf, modff, modfl