scalbn, scalbln

 

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Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

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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       scalbnf( float arg, int exp );		(since C99)
double      scalbn( double arg, int exp );		(since C99)
long double scalbnl( long double arg, int exp );		(since C99)
float       scalblnf( float arg, long exp );		(since C99)
double      scalbln( double arg, long exp );		(since C99)
long double scalblnl( long double arg, long exp );		(since C99)

Multiplies a floating point value arg by FLT_RADIX raised to power exp. On binary systems it is equivalent to ldexp().

Parameters

arg	-	floating point value
exp	-	integer value

Return value

Returns arg×FLT_RADIXexp.

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("FLT_RADIX = %d\n", FLT_RADIX);
    printf("\n");
 
    printf("scalbn(1.0,+1023)   = %g\n",    scalbn(1.0,+1023));     /* 1 * 2^(+1023)  */
    printf("scalbn(1.0,-1074)   = %g\n",    scalbn(1.0,-1074));     /* 1 * 2^(-1074)  */
    printf("scalbn(5.0,0)       = %+.1f\n", scalbn(5.0,0));         /* 5 * 2^0        */
    printf("scalbn(+0.0,1)      = %+.1f\n", scalbn(+0.0,1));        /* 0 * 2^1        */
    printf("scalbn(-0.0,1)      = %+.1f\n", scalbn(-0.0,1));
    printf("scalbn(+INFINITY,1) = %+f\n",   scalbn(+INFINITY,1));   /* INFINITY * 2^1 */
    printf("scalbn(-INFINITY,1) = %+f\n",   scalbn(-INFINITY,1));
    printf("\n");
 
    /* "inexact" and "overflow" floating-point exceptions */
    /* Overflow does not set errno.                       */
    /* 1 * 2^(+1024)                                      */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("scalbn(1.0,1024)    = %f\n",   scalbn(1.0,1024));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
    printf("\n");
 
    /* "inexact" and "underflow" floating-point exceptions */
    /* Underflow does not set errno.                       */
    /* 1 * 2^(-1075)                                       */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("scalbn(1.0,-1075)   = %g\n",   scalbn(1.0,-1075));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
 
    return 0;
}

Possible output:

FLT_RADIX = 2
 
scalbn(1.0,1023)    = 8.98847e+307
scalbn(1.0,-1074)   = 4.94066e-324
scalbn(5.0,0)       = +5.0
scalbn(+0.0,1)      = +0.0
scalbn(-0.0,1)      = -0.0
scalbn(+INFINITY,1) = +inf
scalbn(-INFINITY,1) = -inf
 
scalbn(1.0,1024)    = inf
Success
current exceptions raised:  FE_INEXACT FE_OVERFLOW
 
scalbn(1.0,-1075)   = 0
Success
current exceptions raised:  FE_INEXACT FE_UNDERFLOW

See also

frexpfrexpffrexpl (C99)(C99)	breaks a number into significand and a power of 2 (function)
ldexpldexpfldexpl (C99)(C99)	multiplies a number by 2 raised to a power (function)
C++ documentation for scalbn