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, 12 insertions, 5 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 815c117308b..23f125c567d 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2015-03-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix minor ldexp issues
+        * floatfns.c (Fldexp): Require 2 args.  Avoid undefined behavior
+        if the exponent is out of 'int' range.  Improve documentation.
+        Fixes: bug#20185
+
 2015-03-24  Daniel Colascione  <dancol@dancol.org>
 
         * process.c (Fprocess_running_child_p): Return number identifier of
diff --git a/src/floatfns.c b/src/floatfns.c
index c68b9bd3a65..072e85776b5 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -185,14 +185,14 @@ If X is zero, both parts (SGNFCAND and EXP) are zero.  */)
   return Fcons (make_float (sgnfcand), make_number (exponent));
 }
 
-DEFUN ("ldexp", Fldexp, Sldexp, 1, 2, 0,
-       doc: /* Construct number X from significand SGNFCAND and exponent EXP.
-Returns the floating point value resulting from multiplying SGNFCAND
-(the significand) by 2 raised to the power of EXP (the exponent).   */)
+DEFUN ("ldexp", Fldexp, Sldexp, 2, 2, 0,
+       doc: /* Return X * 2**EXP, as a floating point number.
+EXP must be an integer.   */)
   (Lisp_Object sgnfcand, Lisp_Object exponent)
 {
   CHECK_NUMBER (exponent);
-  return make_float (ldexp (XFLOATINT (sgnfcand), XINT (exponent)));
+  int e = min (max (INT_MIN, XINT (exponent)), INT_MAX);
+  return make_float (ldexp (XFLOATINT (sgnfcand), e));
 }
 
 DEFUN ("exp", Fexp, Sexp, 1, 1, 0,