Open System Services Library Calls Reference Manual (G06.29+, H06.08+, J06.03+)

OSS Library Calls (i - m) log(3)
NAME
log - Computes the natural logarithm function
LIBRARY
G-series native Guardian processes: $SYSTEM.SYSnn.ZCRESRL
G-series native OSS processes: /G/system/sysnn/zcresrl
H-series and J-series native Guardian processes: $SYSTEM.ZDLLnnn.ZCREDLL
32-bit H-series and J-series OSS processes: /G/system/zdllnnn/zcredll
64-bit H-series and J-series OSS processes: /G/system/zdllnnn/ycredll
SYNOPSIS
#include <math.h>
double log(
double x);
PARAMETERS
x Specifies a double value.
DESCRIPTION
The log( ) function computes the natural logarithm of x.
NOTES
This function supports both IEEE Std 754-1985 floating-point and Tandem floating-point values
in the native environment. IEEE values can include NaN and infinity, and the sign of 0.0 (zero)
can be either positive or negative. Refer to the fp_class(3) reference page for a description of
IEEE value classes.
Guardian functions are available to convert between floating-point formats. Refer to the Guar-
dian Programmer’s Guide for a discussion of floating-point conversions.
RETURN VALUES
The log( ) function returns the natural logarithm of x. The value of x must be positive.
For IEEE floating-point data, if the value of x is NaN, NaN is returned. If the value of x is posi-
tive infinity, positive infinity is returned.
If x is negative, either -HUGE_VALis returned for Tandem floating-point data or NaN is
returned for IEEE floating-point data, and errno is set to [EDOM]. If x is 0.0 (zero),
-HUGE_VALis returned and errno is set to [ERANGE].
ERRORS
If any of the following conditions occurs, the log( ) function sets errno to the corresponding
value:
[EDOM] The value of x is negative.
[ERANGE] The value of x is 0.0 (zero).
RELATED INFORMATION
Functions: exp(3), fp_class(3), isnan(3), log10(3), pow(3), sinh(3).
STANDARDS CONFORMANCE
This function conforms to the XPG4 Version 2 specification with extensions when used for IEEE
floating-point format data. This function conforms to the XPG4 Version 2 specification without
extensions when used for Tandem floating-point data.
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