<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW --- - Undefined operation in tgsi_ureg.c left shift of 1 by 31 places cannot be represented in type 'int'" href="https://bugs.freedesktop.org/show_bug.cgi?id=80266#c9">Comment # 9</a> on <a class="bz_bug_link bz_status_NEW " title="NEW --- - Undefined operation in tgsi_ureg.c left shift of 1 by 31 places cannot be represented in type 'int'" href="https://bugs.freedesktop.org/show_bug.cgi?id=80266">bug 80266</a> from <a class="email" href="mailto:zeccav@gmail.com" title="Vittorio <zeccav@gmail.com>"> Vittorio</a> <pre>(In reply to <a href="show_bug.cgi?id=80266#c6">comment #6</a>) > I'm sure that technically shifting any bits into the sign bit of a signed > number produces undefined behavior according to C99, so yes, (1<<31) > technically is undefined. As a matter of practicality, on basically any CPU, > 1<<31 will produce a valid negative number, but the compiler sees it as > trying to assign the constant 2147483648 to a 32-bit signed container, which > is outside of the 2^31-1 range that it can accept. > > In the C abstract machine, this would be a serious problem. Obviously you > can make such an assignment in hardware, but the result (when interpreted as > signed) is not a value of 2147483648, but a value of -2147483648, which is > why the compiler gives a warning. It's weird to read that (1<<31) is less > than 0. If you don't really mean to assign a value of -2147483648 or > 2147483648 and just want a bit pattern, using unsigned is almost always the > way to go. > > I know that Solaris Studio happens to give a warning for the same case, if > that means anything. Thanks for the appreciated explanation. Maybe substituting 1<<31 with 1U<<31 clears any undefined behaviour on the many architectures where mesa runs.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the assignee for the bug.</li> </ul> </body> </html>