* bug#20185: 24.4.50; problem with built-in function "ldexp" Emacs Ver: 24.4.50.1
2015-03-23 20:29 bug#20185: 24.4.50; problem with built-in function "ldexp" Emacs Ver: 24.4.50.1 Bernard Hurley
@ 2015-03-24 18:57 ` Paul Eggert
0 siblings, 0 replies; 2+ messages in thread
From: Paul Eggert @ 2015-03-24 18:57 UTC (permalink / raw)
To: Bernard Hurley; +Cc: 20185-done
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Thanks for catching that bug. While fixing it I noticed some related
minor glitches with ldexp, so I installed the attached patch.
[-- Attachment #2: 0001-Fix-minor-ldexp-issues.patch --]
[-- Type: text/x-patch, Size: 3162 bytes --]
From 68a58397370381fd9b5d08f5cc16a5afa2b5fd26 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Tue, 24 Mar 2015 11:42:53 -0700
Subject: [PATCH] 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
---
doc/lispref/ChangeLog | 4 ++++
doc/lispref/numbers.texi | 12 +++++++++---
src/ChangeLog | 7 +++++++
src/floatfns.c | 10 +++++-----
4 files changed, 25 insertions(+), 8 deletions(-)
diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index a546306..9b1bbb3 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 8d1d3a7..7b4a0a6 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
diff --git a/src/ChangeLog b/src/ChangeLog
index 815c117..23f125c 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 c68b9bd..072e857 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));
}
\f
DEFUN ("exp", Fexp, Sexp, 1, 1, 0,
--
2.1.0
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