# 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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