NAME

scalbln, scalblnf, scalblnl, scalbn, scalbnf, scalbnl — compute exponent using FLT_RADIX

SYNOPSIS

#include <math.h>

double scalbln(double x, long n);
float scalblnf(float x, long n);
long double scalblnl(long double x, long n);
double scalbn(double x, int n);
float scalbnf(float x, int n);
long double scalbnl(long double x, int n);


DESCRIPTION

^[CX] 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.1-2024 defers to the ISO C standard.

These functions shall compute x * FLT_RADIXⁿ efficiently, not normally by computing FLT_RADIXⁿ explicitly.

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

RETURN VALUE

Upon successful completion, these functions shall return x * FLT_RADIXⁿ.

^[MX] If the calculation does not overflow or underflow, the returned value shall be exact and shall be independent of the current rounding direction mode.

If the result would cause overflow, a range error shall occur and these functions shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (according to the sign of x) as appropriate for the return type of the function.

If the correct value would cause underflow, ^[MXX]  and is not representable,  a range error may occur, and scalbln(), scalblnf(), scalblnl(), scalbn(), scalbnf(), and scalbnl() 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, LDBL_MIN, DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

^[MX] If x is NaN, a NaN shall be returned.

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

If n 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.

ERRORS

These functions shall fail if:

Range Error

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:

Range Error

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.

EXAMPLES

None.

APPLICATION USAGE

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.

RATIONALE

These functions are named so as to avoid conflicting with the historical definition of the scalb() function from the Single UNIX Specification. The difference is that the scalb() function has a second argument of double instead of int. The scalb() function is not part of the ISO C standard. The three functions whose second type is long are provided because the factor required to scale from the smallest positive floating-point value to the largest finite one, on many implementations, is too large to represent in the minimum-width int format.

FUTURE DIRECTIONS

None.

SEE ALSO

feclearexcept, fetestexcept

XBD 4.23 Treatment of Error Conditions for Mathematical Functions, <math.h>

CHANGE HISTORY

First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0521 [68] and XSH/TC1-2008/0522 [68] are applied.

Issue 8

Austin Group Defect 1302 is applied, aligning these functions with the ISO/IEC 9899:2018 standard.