ldexp(), ldexpf(), ldexpl() — Multiply by a power of two

Standards

Standards / Extensions	C or C++	Dependencies
ISO C POSIX.1 XPG4 XPG4.2 ISO/ANSI C++ C99 Single UNIX Specification, Version 3 C++ TR1 C99	both

Format

#include <math.h>

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

General description

Calculates the value of x*(2^exp).

Restriction: The ldexpf() and ldexpl() functions do not support the _FP_MODE_VARIABLE feature test macro.

Returned value

Returns the calculated value.

Otherwise, if the correct calculated value is outside the range of representable values, ±HUGE_VAL is returned, according to the sign of the value. The value ERANGE is stored in errno to indicate that the result was out of range.

Special behavior for XPG4.2:

Error Code: Description
ERANGE: The result underflowed. ldexp() returns 0.0.

Example

CELEBL02

⁄* CELEBL02                                      

   This example computes  y = 1.5*&lpar.2**5&rpar.                              
                                                                                
 *⁄                                                                             
#include <math.h>                                                               
#include <stdio.h>                                                              
                                                                                
int main(void)                                                                  
{                                                                               
   double x, y;                                                                 
   int p;                                                                       
                                                                                
   x = 1.5;                                                                     
   p = 5;                                                                       
   y = ldexp(x,p);                                                              
                                                                                
   printf("%lf times 2 to the power of %d is %Lf\n", x, p, y);                  
}

Output

1.500000 times 2 to the power of 5 is 48.000000