The Open Group Base Specifications Issue 7
IEEE Std 1003.1, 2013 Edition
Copyright © 2001-2013 The IEEE and The Open Group

NAME

exp2, exp2f, exp2l - exponential base 2 functions

SYNOPSIS

#include <math.h>

double exp2(double
x);
float exp2f(float
x);
long double exp2l(long double
x);

DESCRIPTION

[CX] [Option Start] 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. [Option End]

These functions shall compute the base-2 exponential of x.

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 2x.

If the correct value would cause overflow, a range error shall occur and exp2(), exp2f(), and exp2l() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively.

If the correct value would cause underflow, [MXX] [Option Start]  and is not representable, [Option End]  a range error may occur, and exp2(), exp2f(), and exp2l() shall return [MXX] [Option Start]  0.0, or [Option End]  (if the IEC 60559 Floating-Point option is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

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

If x is ±0, 1 shall be returned.

If x is -Inf, +0 shall be returned.

If x is +Inf, x shall be returned. [Option End]

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

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.


The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

For IEEE Std 754-1985 double, 1024 <= x implies exp2(x) has overflowed. The value x < -1022 implies exp(x) has underflowed.

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

None.

FUTURE DIRECTIONS

None.

SEE ALSO

exp, feclearexcept, fetestexcept, isnan, log

XBD 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/TC1-2008/0108 [68] and XSH/TC1-2008/0109 [68] are applied.

End of informative text.

 

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