[patch] pow.3: Add note on performance characteristics of pow

[Manuel López-Ibáñez]

Hello,

This patch documents
https://sourceware.org/bugzilla/show_bug.cgi?id=13932 as requested in
https://sourceware.org/bugzilla/show_bug.cgi?id=15267. It would be
nice to add more details, but it seems the behavior and its
consequences is not well understood. The purpose of the note is to
warn users of this behavior and thus avoid frustration
(http://entropymine.com/imageworsener/slowpow/).

This is my first patch. I followed (hopefully correctly) the instructions here:
https://www.kernel.org/doc/man-pages/patches.html

Cheers,

Manuel.
-------------- next part --------------
diff --git a/man3/pow.3 b/man3/pow.3
index d0a2ea8..3d2151a 100644
--- a/man3/pow.3
+++ b/man3/pow.3
@@ -320,6 +320,17 @@ The variant returning
 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 inputs than for other nearby
+inputs. The inputs that produce such behavior are different for
+.BR powf (),
+.BR pow ()
+and
+.BR powl ().
+
 In glibc 2.9 and earlier,
 .\"
 .\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6776