| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
| .\" <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
| .\" |
| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) |
| .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no> |
| .\" Modified 2002-07-27 by Walter Harms |
| .\" (walter.harms@informatik.uni-oldenburg.de) |
| .TH POW 3 2016-03-15 "" "Linux Programmer's Manual" |
| .SH NAME |
| pow, powf, powl \- power functions |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .sp |
| .BI "double pow(double " x ", double " y ); |
| .br |
| .BI "float powf(float " x ", float " y ); |
| .br |
| .BI "long double powl(long double " x ", long double " y ); |
| .fi |
| .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 powf (), |
| .BR powl (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .RE |
| .ad |
| .SH DESCRIPTION |
| These functions return the value of |
| .I x |
| raised to the |
| power of |
| .IR y . |
| .SH RETURN VALUE |
| On success, these functions return the value of |
| .I x |
| to the power of |
| .IR y . |
| |
| If |
| .I x |
| is a finite value less than 0, and |
| .I y |
| is a finite noninteger, a domain error occurs, |
| .\" The domain error is generated at least as far back as glibc 2.4 |
| and a NaN is returned. |
| |
| If the result overflows, |
| a range error occurs, |
| .\" The range error is generated at least as far back as glibc 2.4 |
| and the functions return |
| .BR HUGE_VAL , |
| .BR HUGE_VALF , |
| or |
| .BR HUGE_VALL , |
| respectively, with the mathematically correct sign. |
| |
| If result underflows, and is not representable, |
| a range error occurs, |
| and 0.0 is returned. |
| .\" POSIX.1 does not specify the sign of the zero, |
| .\" but http://sources.redhat.com/bugzilla/show_bug.cgi?id=2678 |
| .\" points out that the zero has the wrong sign in some cases. |
| |
| Except as specified below, if |
| .I x |
| or |
| .I y |
| is a NaN, the result is a NaN. |
| |
| If |
| .I x |
| is +1, the result is 1.0 (even if |
| .I y |
| is a NaN). |
| |
| If |
| .I y |
| is 0, the result is 1.0 (even if |
| .I x |
| is a NaN). |
| |
| If |
| .I x |
| is +0 (\-0), |
| and |
| .I y |
| is an odd integer greater than 0, |
| the result is +0 (\-0). |
| |
| If |
| .I x |
| is 0, |
| and |
| .I y |
| greater than 0 and not an odd integer, |
| the result is +0. |
| |
| If |
| .I x |
| is \-1, |
| and |
| .I y |
| is positive infinity or negative infinity, |
| the result is 1.0. |
| |
| If the absolute value of |
| .I x |
| is less than 1, |
| and |
| .I y |
| is negative infinity, |
| the result is positive infinity. |
| |
| If the absolute value of |
| .I x |
| is greater than 1, |
| and |
| .I y |
| is negative infinity, |
| the result is +0. |
| |
| If the absolute value of |
| .I x |
| is less than 1, |
| and |
| .I y |
| is positive infinity, |
| the result is +0. |
| |
| If the absolute value of |
| .I x |
| is greater than 1, |
| and |
| .I y |
| is positive infinity, |
| the result is positive infinity. |
| |
| If |
| .I x |
| is negative infinity, |
| and |
| .I y |
| is an odd integer less than 0, |
| the result is \-0. |
| |
| If |
| .I x |
| is negative infinity, |
| and |
| .I y |
| less than 0 and not an odd integer, |
| the result is +0. |
| |
| If |
| .I x |
| is negative infinity, |
| and |
| .I y |
| is an odd integer greater than 0, |
| the result is negative infinity. |
| |
| If |
| .I x |
| is negative infinity, |
| and |
| .I y |
| greater than 0 and not an odd integer, |
| the result is positive infinity. |
| |
| If |
| .I x |
| is positive infinity, |
| and |
| .I y |
| less than 0, |
| the result is +0. |
| |
| If |
| .I x |
| is positive infinity, |
| and |
| .I y |
| greater than 0, |
| the result is positive infinity. |
| |
| If |
| .I x |
| is +0 or \-0, |
| and |
| .I y |
| is an odd integer less than 0, |
| a pole error occurs and |
| .BR HUGE_VAL , |
| .BR HUGE_VALF , |
| or |
| .BR HUGE_VALL , |
| is returned, |
| with the same sign as |
| .IR x . |
| |
| If |
| .I x |
| is +0 or \-0, |
| and |
| .I y |
| is less than 0 and not an odd integer, |
| a pole error occurs and |
| .\" The pole error is generated at least as far back as glibc 2.4 |
| .RB + HUGE_VAL , |
| .RB + HUGE_VALF , |
| or |
| .RB + HUGE_VALL , |
| is returned. |
| .SH ERRORS |
| .\" FIXME . review status of this error |
| .\" longstanding bug report for glibc: |
| .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=369 |
| .\" For negative x, and -large and +large y, glibc 2.8 gives incorrect |
| .\" results |
| .\" pow(-0.5,-DBL_MAX)=nan |
| .\" EDOM FE_INVALID nan; fail-errno fail-except fail-result; |
| .\" FAIL (expected: range-error-overflow (ERANGE, FE_OVERFLOW); +INF) |
| .\" |
| .\" pow(-1.5,-DBL_MAX)=nan |
| .\" EDOM FE_INVALID nan; fail-errno fail-except fail-result; |
| .\" FAIL (expected: range-error-underflow (ERANGE, FE_UNDERFLOW); +0) |
| .\" |
| .\" pow(-0.5,DBL_MAX)=nan |
| .\" EDOM FE_INVALID nan; fail-errno fail-except fail-result; |
| .\" FAIL (expected: range-error-underflow (ERANGE, FE_UNDERFLOW); +0) |
| .\" |
| .\" pow(-1.5,DBL_MAX)=nan |
| .\" EDOM FE_INVALID nan; fail-errno fail-except fail-result; |
| .\" FAIL (expected: range-error-overflow (ERANGE, FE_OVERFLOW); +INF) |
| 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 negative, and \fIy\fP is a finite noninteger |
| .I errno |
| is set to |
| .BR EDOM . |
| An invalid floating-point exception |
| .RB ( FE_INVALID ) |
| is raised. |
| .TP |
| Pole error: \fIx\fP is zero, and \fIy\fP is negative |
| .I errno |
| is set to |
| .BR ERANGE |
| (but see BUGS). |
| A divide-by-zero floating-point exception |
| .RB ( FE_DIVBYZERO ) |
| is raised. |
| .TP |
| Range error: the result overflows |
| .I errno |
| is set to |
| .BR ERANGE . |
| An overflow floating-point exception |
| .RB ( FE_OVERFLOW ) |
| is raised. |
| .TP |
| Range error: the result underflows |
| .I errno |
| is set to |
| .BR ERANGE . |
| An underflow floating-point exception |
| .RB ( FE_UNDERFLOW ) |
| is raised. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lbw21 lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR pow (), |
| .BR powf (), |
| .BR powl () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| |
| The variant returning |
| .I double |
| also conforms to |
| SVr4, 4.3BSD, C89. |
| .SH BUGS |
| On 64-bits, |
| .\" |
| .\" https://sourceware.org/bugzilla/show_bug.cgi?id=13932 |
| .BR pow () |
| may be more than 10,000 times slower for some (rare) inputs |
| than for other nearby inputs. |
| This affects only |
| .BR pow (), |
| and not |
| .BR powf () |
| nor |
| .BR powl (). |
| |
| In glibc 2.9 and earlier, |
| .\" |
| .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6776 |
| when a pole error occurs, |
| .I errno |
| is set to |
| .BR EDOM |
| instead of the POSIX-mandated |
| .BR ERANGE . |
| Since version 2.10, |
| .\" or possibly 2.9, I haven't found the source code change |
| .\" and I don't have a 2.9 system to test |
| glibc does the right thing. |
| |
| If |
| .I x |
| is negative, |
| then large negative or positive |
| .I y |
| values yield a NaN as the function result, with |
| .I errno |
| set to |
| .BR EDOM , |
| and an invalid |
| .RB ( FE_INVALID ) |
| floating-point exception. |
| For example, with |
| .BR pow (), |
| one sees this behavior when the absolute value of |
| .I y |
| is greater than about 9.223373e18. |
| .\" see bug http://sources.redhat.com/bugzilla/show_bug.cgi?id=3866 |
| .\" and http://sources.redhat.com/bugzilla/show_bug.cgi?id=369 |
| |
| In version 2.3.2 and earlier, |
| .\" FIXME . Actually, 2.3.2 is the earliest test result I have; so yet |
| .\" to confirm if this error occurs only in 2.3.2. |
| when an overflow or underflow error occurs, glibc's |
| .BR pow () |
| generates a bogus invalid floating-point exception |
| .RB ( FE_INVALID ) |
| in addition to the overflow or underflow exception. |
| .SH SEE ALSO |
| .BR cbrt (3), |
| .BR cpow (3), |
| .BR sqrt (3) |