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Date: Fri, 09 Oct 2015 03:16:16 +0300 From: Alexander Cherepanov <ch3root@...nwall.com> To: discussions@...sword-hashing.net Subject: Re: [PHC] Specification of a modular crypt format (2) On 2015-10-04 03:24, Thomas Pornin wrote: > On Sun, Oct 04, 2015 at 03:07:07AM +0300, Alexander Cherepanov wrote: >> but if value > INT_MAX / 10 the result of multiplication is "not in >> the range of representable values for its type". This is an >> undefined behavior and the result of the whole program run is >> undefined (nasal demons et al.). > > As an added information, consider that clang and gcc can be invoked > with the "-ftrapv" command-line option; with that option, the generated > code specifically checks for overflows on signed integers (for > additions, subtractions and multiplications, says the gcc > documentation). When an overflow occurs, a trap is triggered (on x86, > this uses the 'ud2' pseudo-opcode). > > I don't think that flag is much used in deployed software, but it can be > convenient for testing. Yes, a nice option. Beware though that it doesn't work in 64-bit mode for gcc at least up to version 4.9: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52478 -- Alexander Cherepanov
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