| .\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>. |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
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| .\" Inspired by a page by Walter Harms created 2002-08-10 |
| .\" |
| .TH ILOGB 3 2016-03-15 "" "Linux Programmer's Manual" |
| .SH NAME |
| ilogb, ilogbf, ilogbl \- get integer exponent of a floating-point value |
| .SH SYNOPSIS |
| .B #include <math.h> |
| .sp |
| .BI "int ilogb(double " x ); |
| .br |
| .BI "int ilogbf(float " x ); |
| .br |
| .BI "int ilogbl(long double " x ); |
| .sp |
| Link with \fI\-lm\fP. |
| .sp |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .sp |
| .ad l |
| .BR ilogb (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| || _XOPEN_SOURCE\ >=\ 500 |
| .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .RE |
| .br |
| .BR ilogbf (), |
| .BR ilogbl (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .RE |
| .ad b |
| .SH DESCRIPTION |
| These functions return the exponent part of their argument |
| as a signed integer. |
| When no error occurs, these functions |
| are equivalent to the corresponding |
| .BR logb (3) |
| functions, cast to |
| .IR int . |
| .SH RETURN VALUE |
| On success, these functions return the exponent of |
| .IR x , |
| as a signed integer. |
| |
| If |
| .I x |
| is zero, then a domain error occurs, and the functions return |
| .\" the POSIX.1 spec for logb() says logb() gives pole error for this |
| .\" case, but for ilogb() it says domain error. |
| .BR FP_ILOGB0 . |
| .\" glibc: The numeric value is either `INT_MIN' or `-INT_MAX'. |
| |
| If |
| .I x |
| is a NaN, then a domain error occurs, and the functions return |
| .BR FP_ILOGBNAN . |
| .\" glibc: The numeric value is either `INT_MIN' or `INT_MAX'. |
| .\" On i386, FP_ILOGB0 and FP_ILOGBNAN have the same value. |
| |
| If |
| .I x |
| is negative infinity or positive infinity, then |
| a domain error occurs, and the functions return |
| .BR INT_MAX . |
| .\" |
| .\" POSIX.1-2001 also says: |
| .\" If the correct value is greater than {INT_MAX}, {INT_MAX} |
| .\" shall be returned and a domain error shall occur. |
| .\" |
| .\" If the correct value is less than {INT_MIN}, {INT_MIN} |
| .\" shall be returned and a domain error shall occur. |
| .SH ERRORS |
| See |
| .BR math_error (7) |
| for information on how to determine whether an error has occurred |
| when calling these functions. |
| .PP |
| The following errors can occur: |
| .TP |
| Domain error: \fIx\fP is 0 or a NaN |
| An invalid floating-point exception |
| .RB ( FE_INVALID ) |
| is raised, and |
| .I errno |
| is set to |
| .BR EDOM |
| (but see BUGS). |
| .IP |
| .TP |
| Domain error: \fIx\fP is an infinity |
| An invalid floating-point exception |
| .RB ( FE_INVALID ) |
| is raised, and |
| .I errno |
| is set to |
| .BR EDOM |
| (but see BUGS). |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lbw27 lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR ilogb (), |
| .BR ilogbf (), |
| .BR ilogbl () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| .SH BUGS |
| .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6794 |
| Before version 2.16, the following bugs existed in the |
| glibc implementation of these functions: |
| .IP * 3 |
| The domain error case where |
| .I x |
| is 0 or a NaN did not cause |
| .I errno |
| to be set or (on some architectures) raise a floating-point exception. |
| .IP * 3 |
| The domain error case where |
| .I x |
| is an infinity did not cause |
| .I errno |
| to be set or raise a floating-point exception. |
| .SH SEE ALSO |
| .BR log (3), |
| .BR logb (3), |
| .BR significand (3) |