Hello, we hit a bug today while cross-compiling a C++ program with mingw32: if random_shuffle or random_sample_n are called with a sequence of elements whose length is higher than RAND_MAX, the functions don't behave as expected because they ignore elements beyond RAND_MAX. This does not happen often on Linux where glibc defines RAND_MAX to 2**31, but mingw32 (all released versions) relies on the very old msvcrt.lib, where RAND_MAX is just 2**15.
I found mentions of this problem in 2011 (http://mingw-users.1079350.n2.nabble.com/RAND-MAX-still-16bit-td6299546.html) and 2006 (https://mingw-users.narkive.com/gAIO4G5V/rand-max-problem-why-is-it-only-16-bit). I'm attaching a proof-of-concept patch that fixes the problem by introducing an embedded xorshift generator, seeded with std::rand (so that the functions still depend on srand — it looks like this is not strictly required by the standard, but it sounds like a good thing to do for backward compatibility with existing programs). I was wondering if this approach is OK or something else is preferred. -- Giovanni Bajo :: ra...@develer.com Develer S.r.l. :: http://www.develer.com
rand.diff
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