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LOG(3) Library Functions Manual LOG(3) NAME log, logf, log10, log10f, log1p, log1pf log2, log2f - logarithm functions LIBRARY Math Library (libm, -lm) SYNOPSIS #include <math.h> double log(double x); float logf(float x); double log10(double x); float log10f(float x); double log1p(double x); float log1pf(float x); double log2(double x); float log2f(float x); DESCRIPTION The following functions compute logarithms: ⊕ The log() and logf() functions return the natural logarithm. ⊕ The log10() and log10f() functions return the base 10 logarithm. ⊕ The log1p() and log1pf() functions return the natural logarithm of (1.0 + x) accurately even for very small values of x. ⊕ The log2() and log2f() functions return the base 2 logarithm. 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 The history of the logarithm functions dates back to Version 6 AT&T UNIX. NetBSD 8.99.34 September 13, 2011 NetBSD 8.99.34