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

OSS Library Calls (i - m) logbl(3)
NAME
logbl - Computes the radix-independent exponent as a long double number
LIBRARY
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>
long double logbl(
long double x);
PARAMETERS
x Specifies the long double value for which the exponent is to be calculated.
DESCRIPTION
The logbl( ) function is a long double version of the logb( ) function; it takes a long double argu-
ment and returns a long double result.
The logbl( ) function returns the unbiased exponent part of the floating-point value given as the x
parameter. The logbl( ) function calculates the integral part of the base-r logarithm (where r is
the radix of the machine’s floating-point arithmetic) of the absolute value of x and returns the
result as a signed floating-point value.
NOTES
The logbl( ) function can be called only by native processes.
This function supports both IEEE Std 754-1985 floating-point and Tandem floating-point values.
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 logbl( ) function returns the exponent of x.
For IEEE floating-point data, the following are true:
• logbl(NaN) returns a quiet NaN.
• When the value of x is positive or negative infinity, logbl( ) returns a value of positive
infinity.
• When the value of x is 0.0 (zero), logbl(0.0) returns a value of -HUGE_VALL and sets
errno to [EDOM].
For Tandem floating-point data, when x has a value of 0.0 (zero), logbl( ) returns the value
-HUGE_VALL and sets errno to [EDOM].
ERRORS
If any of the following conditions occurs, the logbl( ) function sets errno to the corresponding
value:
[EDOM] The x parameter is 0.0 (zero).
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