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log2, log2f, log2l - compute base 2 logarithm functions

#include <math.h>

double log2(doublex);

float log2f(floatx);

long double log2l(long doublex);

These functions shall compute the base 2 logarithm of their argument

x, log_2(x).An application wishing to check for error situations should set

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the base 2 logarithm of

x.If

xis ±0, a pole error shall occur andlog2(),log2f(), andlog2l() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.For finite values of

xthat are less than 0, or ifxis -Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.If

xis NaN, a NaN shall be returned.If

xis 1, +0 shall be returned.If

xis +Inf,xshall be returned.

These functions shall fail if:

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then

Domain Error The finite value of xis less than zero, orxis -Inf.If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errnoshall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.Pole Error The value of xis zero.errnoshall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

The following sections are informative.

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() ,fetestexcept() ,log() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions,<math.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group |
LOG2 (P) | 2003 |