LDEXP(3) Library Functions Manual LDEXP(3)

ldexp ldexpf ldexpl — load exponent of a floating-point number

#include <math.h>

double ldexp(double x, int exp);
float ldexpf(float x, int exp);
long double ldexpl(long double x, int exp);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

These functions shall compute the quantity x * 2 exp.

An application wishing to check for error situations should set errno to zero and call (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return x multiplied by 2, raised to the power exp.

If these functions would cause overflow, a range error shall occur and ldexp (), ldexpf (), and ldexpl () shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (according to the sign of x), respectively.

If the correct value would cause underflow, [MXX] and is not representable, a range error may occur, and ldexp (), ldexpf (), and ldexpl () shall return [MXX] 0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

If x is NaN, a NaN shall be returned.

If x is ±0 or ±Inf, x shall be returned.

If exp is 0, x shall be returned.

[MXX] If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

These functions shall fail if:

The result overflows. If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

These functions may fail if:

The result underflows. If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised.

None.

On error, the expressions ( math_errhandling & MATH_ERRNO) and ( math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

None.

None.

feclearexcept(3), fetestexcept(3), frexp(3), isnan(3)

XBD V1_chap04(7), <math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The ldexpf () and ldexpl () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0352 [68] and XSH/TC1-2008/0353 [68] are applied.

January 1, 2016 posix.fail