log(3) - NetBSD Manual Pages

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LOG(3)                  NetBSD Library Functions Manual                 LOG(3)


NAME
log, logf, logl, log10, log10f, log10l, log1p, log1pf, log1pl, log2, log2f log2l -- logarithm functions
LIBRARY
Math Library (libm, -lm)
SYNOPSIS
#include <math.h> double log(double x); float logf(float x); long double logl(long double x); double log10(double x); float log10f(float x); log double log10l(long double x); double log1p(double x); float log1pf(float x); long double log1pl(long double x); double log2(double x); float log2f(float x); long double log2l(long double x);
DESCRIPTION
The following functions compute logarithms: The log(), logf() and logl() functions return the natural loga- rithm. The log10(), log10f() and log10l() functions return the base 10 logarithm. The log1p(), log1pf() and log1pl() functions return the natural logarithm of (1.0 + x) accurately even for very small values of x. The log2(), log2f() and log2l() functions return the base 2 loga- rithm.
RETURN VALUES
Upon successful completion, the functions return the logarithm of x as described above. Otherwise the following may occur: 1. If x is NaN, all functions return NaN. 2. If x is positive infinity, all functions return x. If x is negative infinity, all functions return NaN. 3. If x is +0.0 or -0.0, the log(), log10(), and log2() families return either -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, whereas the log1p() family returns x. 4. If x is +1.0, the log(), log10(), and log2() families return +0.0. If x is -1.0, the log1p() family returns -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL. In addition, on a VAX, errno is set to EDOM and the reserved operand is returned by log() unless x > 0, by log1p() unless x > -1.
SEE ALSO
exp(3), ilogb(3), math(3)
STANDARDS
The described functions conform to ISO/IEC 9899:1999 (``ISO C99'').
HISTORY
A log() function appeared in Version 1 AT&T UNIX. NetBSD 10.99 January 24, 2024 NetBSD 10.99
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