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diff --git a/man3/pow.3 b/man3/pow.3 new file mode 100644 index 0000000..3f0be5c --- /dev/null +++ b/man3/pow.3 @@ -0,0 +1,384 @@ +'\" t +.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) +.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk +.\" <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" 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 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +pow, powf, powl \- power functions +.SH LIBRARY +Math library +.RI ( libm ", " \-lm ) +.SH SYNOPSIS +.nf +.B #include <math.h> +.PP +.BI "double pow(double " x ", double " y ); +.BI "float powf(float " x ", float " y ); +.BI "long double powl(long double " x ", long double " y ); +.fi +.PP +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.PP +.BR powf (), +.BR powl (): +.nf + _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L + || /* Since glibc 2.19: */ _DEFAULT_SOURCE + || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE +.fi +.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 . +.PP +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. +.PP +If result underflows, and is not representable, +a range error occurs, +and 0.0 with the appropriate sign is returned. +.\" POSIX.1 does not specify the sign of the zero, +.\" but https://www.sourceware.org/bugzilla/show_bug.cgi?id=2678 +.\" points out that the zero has the wrong sign in some cases. +.PP +.\" pow(\(+-0, <0 [[odd]]) = HUGE_VAL* +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 . +.PP +.\" pow(\(+-0, <0 [[!odd]]) = HUGE_VAL* +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. +.PP +.\" pow(\(+-0, >0 [[odd]]) = \(+-0 +If +.I x +is +0 (\-0), +and +.I y +is an odd integer greater than 0, +the result is +0 (\-0). +.PP +.\" pow(\(+-0, >0 [[!odd]]) = +0 +If +.I x +is 0, +and +.I y +greater than 0 and not an odd integer, +the result is +0. +.PP +.\" pow(-1, \(+-INFINITY) = 1.0 +If +.I x +is \-1, +and +.I y +is positive infinity or negative infinity, +the result is 1.0. +.PP +.\" pow(+1, y) = 1.0 +If +.I x +is +1, the result is 1.0 (even if +.I y +is a NaN). +.PP +.\" pow(x, \(+-0) = 1.0 +If +.I y +is 0, the result is 1.0 (even if +.I x +is a NaN). +.PP +.\" pow(<0, y) = NaN +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. +.PP +.\" pow(|x|<1, -INFINITY) = INFINITY +If the absolute value of +.I x +is less than 1, +and +.I y +is negative infinity, +the result is positive infinity. +.PP +.\" pow(|x|>1, -INFINITY) = +0 +If the absolute value of +.I x +is greater than 1, +and +.I y +is negative infinity, +the result is +0. +.PP +.\" pow(|x|<1, INFINITY) = +0 +If the absolute value of +.I x +is less than 1, +and +.I y +is positive infinity, +the result is +0. +.PP +.\" pow(|x|>1, INFINITY) = INFINITY +If the absolute value of +.I x +is greater than 1, +and +.I y +is positive infinity, +the result is positive infinity. +.PP +.\" pow(-INFINITY, <0 [[odd]]) = -0 +If +.I x +is negative infinity, +and +.I y +is an odd integer less than 0, +the result is \-0. +.PP +.\" pow(-INFINITY, <0 [[!odd]]) = +0 +If +.I x +is negative infinity, +and +.I y +less than 0 and not an odd integer, +the result is +0. +.PP +.\" pow(-INFINITY, >0 [[odd]]) = -INFINITY +If +.I x +is negative infinity, +and +.I y +is an odd integer greater than 0, +the result is negative infinity. +.PP +.\" pow(-INFINITY, >0 [[!odd]]) = INFINITY +If +.I x +is negative infinity, +and +.I y +greater than 0 and not an odd integer, +the result is positive infinity. +.PP +.\" pow(INFINITY, <0) = +0 +If +.I x +is positive infinity, +and +.I y +less than 0, +the result is +0. +.PP +.\" pow(INFINITY, >0) = INFINITY +If +.I x +is positive infinity, +and +.I y +greater than 0, +the result is positive infinity. +.PP +.\" pow(NaN, y) or pow(x, NaN) = NaN +Except as specified above, if +.I x +or +.I y +is a NaN, the result is a NaN. +.SH ERRORS +.\" FIXME . review status of this error +.\" longstanding bug report for glibc: +.\" https://www.sourceware.org/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 +.B 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; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR pow (), +.BR powf (), +.BR powl () +T} Thread safety MT-Safe +.TE +.sp 1 +.SH STANDARDS +C11, POSIX.1-2008. +.SH HISTORY +C99, POSIX.1-2001. +.PP +The variant returning +.I double +also conforms to +SVr4, 4.3BSD, C89. +.SH BUGS +.SS Historical bugs (now fixed) +Before glibc 2.28, +.\" https://sourceware.org/bugzilla/show_bug.cgi?id=13932 +on some architectures (e.g., x86-64) +.BR pow () +may be more than 10,000 times slower for some inputs +than for other nearby inputs. +This affects only +.BR pow (), +and not +.BR powf () +nor +.BR powl (). +This problem was fixed +.\" commit c3d466cba1692708a19c6ff829d0386c83a0c6e5 +in glibc 2.28. +.PP +A number of bugs +.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=3866 +in the glibc implementation of +.BR pow () +were fixed in glibc 2.16. +.PP +In glibc 2.9 and earlier, +.\" +.\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6776 +when a pole error occurs, +.I errno +is set to +.B EDOM +instead of the POSIX-mandated +.BR ERANGE . +Since glibc 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. +.PP +In glibc 2.3.2 and earlier, +.\" Actually, glibc 2.3.2 is the earliest test result I have; so yet +.\" to confirm if this error occurs only in glibc 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) |