Fix minor ldexp issues

* doc/lispref/numbers.texi (Float Basics): Improve ldexp documentation.
* src/floatfns.c (Fldexp): Require 2 args.  Avoid undefined behavior
if the exponent is out of 'int' range.  Improve documentation.
Fixes: bug#20185

2 files changed, 13 insertions, 3 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index a546306f9e4..9b1bbb357a5 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,7 @@
+2015-03-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+        * numbers.texi (Float Basics): Improve ldexp documentation.
+
 2015-03-23  Eli Zaretskii  <eliz@gnu.org>
 
         * commands.texi (Event Input Misc): Fix incorrect usage of @code.
diff --git a/doc/lispref/numbers.texi b/doc/lispref/numbers.texi
index 8d1d3a798eb..7b4a0a6d407 100644
--- a/doc/lispref/numbers.texi
+++ b/doc/lispref/numbers.texi
@@ -265,9 +265,15 @@ If @var{x} is a NaN, then @var{s} is also a NaN@.
 If @var{x} is zero, then @var{e} is 0.
 @end defun
 
-@defun ldexp sig &optional exp
-This function returns a floating-point number corresponding to the
-significand @var{sig} and exponent @var{exp}.
+@defun ldexp s e
+Given a numeric significand @var{s} and an integer exponent @var{e},
+this function returns the floating point number
+@ifnottex
+@var{s} * 2**@var{e}.
+@end ifnottex
+@tex
+@math{s 2^e}.
+@end tex
 @end defun
 
 @defun copysign x1 x2