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, 1 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index a2f96f4bf92..475b4b26fdb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -469,6 +469,7 @@ file using `set-file-extended-attributes'.
 ** New macro with-eval-after-load.  Like eval-after-load, but better behaved.
 
 ** Obsoleted functions:
+*** `log10'
 *** `dont-compile'
 *** `lisp-complete-symbol'
 *** `field-complete'