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ldexp, ldexpf, ldexpl

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


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 higher

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


Floating-point value.

Integer exponent.

Return value

The ldexp functions return the value of x * 2exp 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.


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.


Routine C header C++ header
ldexp, ldexpf, ldexpl <math.h> <cmath>
ldexp macro <tgmath.h>

For compatibility information, see Compatibility.


// 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 );


4.0 times two to the power of 3 is 32.0

See also

Math and floating-point support
modf, modff, modfl