ldexp

 

C

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Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

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Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

 

Common mathematical functions

Functions
Basic operations
abslabsllabsimaxabs (C99) fabs divldivlldivimaxdiv (C99) fmod	remainder (C99) remquo (C99) fma (C99) fmax (C99) fmin (C99) fdim (C99) nannanfnanl (C99)(C99)(C99)
Exponential functions
exp exp2 (C99) expm1 (C99)	log log10 log1p (C99) log2 (C99)
Power functions
sqrt cbrt (C99)	hypot (C99) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C99) acosh (C99) atanh (C99)
Error and gamma functions
erf (C99) erfc (C99)	lgamma (C99) tgamma (C99)
Nearest integer floating point operations
ceil floor roundlroundllround (C99)(C99)(C99)	trunc (C99) nearbyint (C99) rintlrintllrint (C99)(C99)(C99)
Floating point manipulation functions
ldexp scalbnscalbln (C99)(C99) ilogb (C99) logb (C99)	frexp modf nextafternexttoward (C99)(C99) copysign (C99)
Classification
fpclassify (C99)
isfinite (C99)
isinf (C99)
isnan (C99)
isnormal (C99)
signbit (C99)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C99)(C99)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C99)(C99)(C99)(C99)(C99)

 

Defined in header <math.h>
float       ldexpf( float arg, int exp );		(since C99)
double      ldexp( double arg, int exp );
long double ldexpl( long double arg, int exp );		(since C99)

Multiplies a floating point value arg by 2 raised to power exp.

Parameters

arg	-	floating point value
exp	-	integer value

Return value

Returns arg×2exp.

If the result is too large for the underlying type, range error occurs and HUGE_VAL is returned.

Example

Run this code

#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <errno.h>
#include <float.h>
#include <string.h>
 
#pragma STDC FENV_ACCESS ON
 
void show_fe_exceptions(void)
{
    printf("current exceptions raised: ");
    if(fetestexcept(FE_DIVBYZERO))     printf(" FE_DIVBYZERO");
    if(fetestexcept(FE_INEXACT))       printf(" FE_INEXACT");
    if(fetestexcept(FE_INVALID))       printf(" FE_INVALID");
    if(fetestexcept(FE_OVERFLOW))      printf(" FE_OVERFLOW");
    if(fetestexcept(FE_UNDERFLOW))     printf(" FE_UNDERFLOW");
    if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none");
    printf("\n");
}
 
int main(void)
{
    printf("ldexp(1.0,+1023)   = %g\n",    ldexp(1.0,+1023));     /* 1 * 2^(+1023)  */
    printf("ldexp(1.0,-1074)   = %g\n",    ldexp(1.0,-1074));     /* 1 * 2^(-1074)  */
    printf("ldexp(5.0,0)       = %+.1f\n", ldexp(5.0,0));         /* 5 * 2^0        */
    printf("ldexp(+0.0,1)      = %+.1f\n", ldexp(+0.0,1));        /* 0 * 2^1        */
    printf("ldexp(-0.0,1)      = %+.1f\n", ldexp(-0.0,1));
    printf("ldexp(+INFINITY,1) = %+f\n",   ldexp(+INFINITY,1));   /* INFINITY * 2^1 */
    printf("ldexp(-INFINITY,1) = %+f\n",   ldexp(-INFINITY,1));
    printf("\n");
 
    /* "inexact" and "overflow" floating-point exceptions */
    /* Overflow does set errno (range error).             */
    /* 1 * 2^(+1024)                                      */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("ldexp(1.0,1024)    = %f\n",   ldexp(1.0,1024));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
    printf("\n");
 
    /* "inexact" and "underflow" floating-point exceptions */
    /* Underflow does set errno (range error).             */
    /* 1 * 2^(-1075)                                       */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("ldexp(1.0,-1075)   = %g\n",   ldexp(1.0,-1075));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
 
    return 0;
}

Possible output:

ldexp(1.0,1023)    = 8.98847e+307
ldexp(1.0,-1074)   = 4.94066e-324
ldexp(5.0,0)       = +5.0
ldexp(+0.0,1)      = +0.0
ldexp(-0.0,1)      = -0.0
ldexp(+INFINITY,1) = +inf
ldexp(-INFINITY,1) = -inf
 
ldexp(1.0,1024)    = inf
Numerical result out of range
current exceptions raised:  FE_INEXACT FE_OVERFLOW
 
ldexp(1.0,-1075)   = 0
Numerical result out of range
current exceptions raised:  FE_INEXACT FE_UNDERFLOW

See also

frexpfrexpffrexpl (C99)(C99)	breaks a number into significand and a power of 2 (function)
scalbnscalbnfscalbnlscalblnscalblnfscalblnl (C99)(C99)(C99)(C99)(C99)(C99)	computes efficiently a number times FLT_RADIX raised to a power (function)
C++ documentation for ldexp