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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../../cpp/../c/numeric/math/ldexp.html below:

ldexp, ldexpf, ldexpl - cppreference.com

#define ldexp( arg, exp )

Multiplies a floating-point value

by the number

raised to the

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.

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.

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.

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.

#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>
#include <stdio.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

• C23 standard (ISO/IEC 9899:2024):

• 7.12.6.6 The ldexp functions (p: TBD)

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

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

• C17 standard (ISO/IEC 9899:2018):

• 7.12.6.6 The ldexp functions (p: TBD)

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

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

• 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

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