| Message ID | a0c911ee-4587-10d6-3c75-74538e7623be@netcologne.de |
|---|---|
| State | New |
| Headers | show |
| Series | [wwwdocs] Mention random number generators in porting_to.html | expand |
Hi Thomas, Am 18.03.23 um 19:23 schrieb Thomas Koenig via Gcc-patches: > Hi, > > Text says it all. OK for web pages? > > Best regards > > Thomas > > Mention issues with integer owerflow for random number generators. > > This mentions the issues with integer overflow and how to work > around them. it's basically fine, although I'd prefer a formulation replacing + <p> GCC 13 includes new optimizations which expose reliance on + non-standard behavior for integer overflow, which was often used + for linear congruential pseudo-random number generators in old + programs. It is recommended to use the intrinsic by something like: GCC 13 includes new optimizations which may change behavior on integer overflow. Traditional code, like linear congruential pseudo-random number generators in old programs and relying on a specific, non-standard behavior may now generate unexpected results. In such cases it is recommended to use the intrinsic ... Thanks for updating the documentation! Harald
diff --git a/htdocs/gcc-13/porting_to.html b/htdocs/gcc-13/porting_to.html index 0ee58802..7d733b16 100644 --- a/htdocs/gcc-13/porting_to.html +++ b/htdocs/gcc-13/porting_to.html @@ -203,11 +203,20 @@ class Alloc <p> Since C++20, there is no <code>rebind</code> member in <code>std::allocator</code>, so deriving your own allocator types from -<code>std::allocator</code> is simpler and doesn't require the derived +<code>std::allocator</code> is simpler and does not require the derived allocator to provide its own <code>rebind</code>. For compatibility with previous C++ standards, the member should still be provided. The converting constructor is still required even in C++20. </p> +<h2 id="fortran">Fortran language issues</h2> +<h3 id="overflow">Behavior on integer overflow</h3> +<p> GCC 13 includes new optimizations which expose reliance on + non-standard behavior for integer overflow, which was often used + for linear congruential pseudo-random number generators in old + programs. It is recommended to use the intrinsic + subroutine <code>RANDOM_NUMBER</code> for random number generators + or, if the old behavior is desired, to use the <code>-fwrapv</code> + option. Note that this option can impact performance. </body> </html>