ldexp, ldexpf, ldexpl

 

C

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headers

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Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

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)	isgreater (C99) isgreaterequal (C99) isless (C99) islessequal (C99) islessgreater (C99) isunordered (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 );	(1)	(since C99)
double      ldexp( double arg, int exp );	(2)
long double ldexpl( long double arg, int exp );	(3)	(since C99)
Defined in header <tgmath.h>
#define ldexp( arg, exp )	(4)	(since C99)

1-3) Multiplies a floating point value arg by the number 2 raised to the exp power.

4) Type-generic macro: If arg has type long double, ldexpl is called. Otherwise, if arg has integer type or the type double, ldexp is called. Otherwise, ldexpf is called, respectively.

Parameters

arg	-	floating point value
exp	-	integer value

Return value

If no errors occur, arg multiplied by 2 to the power of exp (arg×2exp
) is returned.

If a range error due to overflow occurs, ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL is returned.

If a range error due to underflow occurs, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• Unless a range error occurs, FE_INEXACT is never raised (the result is exact)
• Unless a range error occurs, the current rounding mode is ignored
• If arg is ±0, it is returned, unmodified
• If arg is ±∞, it is returned, unmodified
• If exp is 0, then arg is returned, unmodified
• If arg is NaN, NaN is returned

Notes

On binary systems (where FLT_RADIX is 2), ldexp is equivalent to scalbn.

The function ldexp ("load exponent"), together with its dual, frexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.

On many implementations, ldexp is less efficient than multiplication or division by a power of two using arithmetic operators.

Example

Run this code

#include <stdio.h>
#include <math.h>
#include <float.h>
#include <errno.h>
#include <fenv.h>
#pragma STDC FENV_ACCESS ON
int main(void)
{
    printf("ldexp(7, -4) = %f\n", ldexp(7, -4));
    printf("ldexp(1, -1074) = %g (minimum positive subnormal double)\n",
            ldexp(1, -1074));
    printf("ldexp(nextafter(1,0), 1024) = %g (largest finite double)\n",
            ldexp(nextafter(1,0), 1024));
    // special values
    printf("ldexp(-0, 10) = %f\n", ldexp(-0.0, 10));
    printf("ldexp(-Inf, -1) = %f\n", ldexp(-INFINITY, -1));
    //error handling
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("ldexp(1, 1024) = %f\n", ldexp(1, 1024));
    if(errno == ERANGE) perror("    errno == ERANGE");
    if(fetestexcept(FE_OVERFLOW)) puts("    FE_OVERFLOW raised");
}

Possible output:

ldexp(7, -4) = 0.437500
ldexp(1, -1074) = 4.94066e-324 (minimum positive subnormal double)
ldexp(nextafter(1,0), 1024) = 1.79769e+308 (largest finite double)
ldexp(-0, 10) = -0.000000
ldexp(-Inf, -1) = -inf
ldexp(1, 1024) = inf
    errno == ERANGE: Numerical result out of range
    FE_OVERFLOW raised

References

• C11 standard (ISO/IEC 9899:2011):

• 7.12.6.6 The ldexp functions (p: 244)

• 7.25 Type-generic math <tgmath.h> (p: 373-375)

• F.10.3.6 The ldexp functions (p: 522)

• C99 standard (ISO/IEC 9899:1999):

• 7.12.6.6 The ldexp functions (p: 225)

• 7.22 Type-generic math <tgmath.h> (p: 335-337)

• F.9.3.6 The ldexp functions (p: 459)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.5.4.3 The ldexp function

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