MirOS Manual: log(3), log10(3), log10f(3), log1p(3), log1pf(3), log2(3), log2f(3), logf(3)

LOG(3)                     BSD Programmer's Manual                      LOG(3)

NAME

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

LIBRARY

     libm

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
     descibed 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.

MirOS BSD #10-current         September 13, 2011                             1

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