log(3) - NetBSD Manual Pages

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


NAME

     log, logf, log10, log10f, log1p, log1pf, log2, log2f -- logarithm func-
     tions


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

     A log() function appeared in Version 1 AT&T UNIX.

NetBSD 10.1                    September 2, 2019                   NetBSD 10.1