Add log2 support and make log10 obsolete for consistency.

* configure.ac (log2): Check for this function.
* doc/lispref/numbers.texi (Math Functions): Remove obsolete function log10.
* lisp/subr.el (log10): Move here from C code, and declare as obsolete.
All uses of (log10 X) replaced with (log X 10).
* src/floatfns.c (Flog) [HAVE_LOG2]: Use log2 if available and if the
base is 2; this is more accurate.
(Flog10): Move to Lisp (marked obsolete there).

1 files changed, 9 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 68138e46b6b..c503da29732 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2013-06-20  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * floatfns.c (Flog10): Move to Lisp (marked obsolete there).
+
+2013-06-20  Rüdiger Sonderfeld <ruediger@c-plusplus.de>
+
+        * floatfns.c (Flog) [HAVE_LOG2]: Use log2 if available and if the
+        base is 2; this is more accurate.
+
 2013-06-19  Juanma Barranquero  <lekktu@gmail.com>
 
         * sound.c (string_default): Move to !WINDOWSNT section.