From: Thomas Koenig <tkoenig@netcologne.de>
To: "fortran@gcc.gnu.org" <fortran@gcc.gnu.org>,
gcc-patches <gcc-patches@gcc.gnu.org>
Subject: [patch, fortran, doc] Explicitly mention undefined overflow
Date: Sun, 19 Mar 2023 09:32:45 +0100 [thread overview]
Message-ID: <eee8f01b-7e2c-c465-eaed-226714dc9655@netcologne.de> (raw)
[-- Attachment #1: Type: text/plain, Size: 238 bytes --]
Here's also an update on the docs to explicitly mention behavior
on overflow.
Maybe this will reach another 0.05% of users...
OK for trunk?
Best regards
Thomas
gcc/fortran/ChangeLog:
* gfortran.texi: Mention behavior on overflow.
[-- Attachment #2: overflow.diff --]
[-- Type: text/x-patch, Size: 1414 bytes --]
diff --git a/gcc/fortran/gfortran.texi b/gcc/fortran/gfortran.texi
index c483e13686d..93c66b18938 100644
--- a/gcc/fortran/gfortran.texi
+++ b/gcc/fortran/gfortran.texi
@@ -820,6 +820,7 @@ might in some way or another become visible to the programmer.
* File operations on symbolic links::
* File format of unformatted sequential files::
* Asynchronous I/O::
+* Behavior on integer overflow::o
@end menu
@@ -1160,6 +1161,23 @@ sytems, such as Linux, it is necessary to specify @option{-pthread},
@c Maybe this chapter should be merged with the 'Standards' section,
@c whenever that is written :-)
+@node Behavior on integer overflow
+@section Behavior on integer overflow
+@cindex integer overflow
+@cindex overflow handling
+
+Integer overflow is prohibited by the Fortran standard. The behavior
+of gfortran on integer overflow is undefined by default. Traditional
+code, like linear congruential pseudo-random number generators in old
+programs that rely on specific, non-standard behavior may generate
+unexpected results. The @option{-fsanitize=undefined} option can be
+used to detect such code at runtime.
+
+It is recommended to use the intrinsic subroutine @code{RANDOM_NUMBER}
+for random number generators or, if the old behavior is desired, to
+use the @option{-fwrapv} option. Note that this option can impact
+performance.
+
@node Extensions
@chapter Extensions
@cindex extensions
next reply other threads:[~2023-03-19 8:32 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-19 8:32 Thomas Koenig [this message]
2023-03-19 13:12 ` Paul Richard Thomas
2023-03-19 17:40 ` Thomas Koenig
2023-03-20 7:14 ` Thomas Koenig
2023-03-20 21:32 ` Harald Anlauf
2023-03-19 13:15 ` Andreas Schwab
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