# ldexp(), ldexpf(), ldexpl()

Multiply a floating-point number by an integral power of 2

## Synopsis:

```#include <math.h>

double ldexp( double x,
int exp );

float ldexp( float x,
int exp );

long double ldexpl( long double x,
int exp );
```

## Arguments:

x
A floating-point number.
exp
The exponent of 2 to multiply x by.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

These functions multiply the floating-point number x by 2exp. A range error may occur.

To check for error situations, use feclearexcept() and fetestexcept():

• Call feclearexcept(FE_ALL_EXCEPT) before calling ldexp(), ldexpf(), or ldexpl().
• On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, then an error has occurred.

## Returns:

x × 2exp

For a correct value that would cause an underflow, these functions return 0.0.

• If these functions would cause an overflow, a range error occurs, and they return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (according to the sign of x), respectively.
• If the correct value would cause an underflow, range error may occur, and these functions return 0.0, or (if IEC 60559 Floating-Point isn't supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
• If x is NaN, the functions return NaN.
• If x is ±0 or ±Inf, x is returned.
• If exp is 0, x is returned.
• If the correct value would cause an underflow, and is representable, a range error may occur, and the correct value is returned.

## Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;
double value;

feclearexcept(FE_ALL_EXCEPT);

value = ldexp( 4.7072345, 5 );

except_flags = fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

printf( "%f\n", value );

return EXIT_SUCCESS;
}
```

produces the output:

```150.631504
```

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No