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So, if we pick a modulus of 0, of course uniform_1 croaks. If our generator really is acceptably random, that should be pretty rare. We add another call, which still doesn't guarantee we don't get two zeros in a row, but if that happens, the PRNG is more likely to be broken or your luck was really bad. We could just bitwise-or in a 1, but I prefer having this canary. As evidence that I have tested this code too infrequently without rdrand, it turns out that PCG32 initialization without rdrand has been quite weak, all this time, and it's quite common to get 0 from uniform32 here as the modulus, much more than it should have been.
Without rdrand, benchmarks were aborting because the first value generated was often zero. Having high-quality seeding has never been a goal of this library, but this was pretty bad. So we mix in an initialization constant (from some other code I wrote using pcg32, which presumably took it from upstream PCG examples or a similar source).
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FYI, I've tested these change and they seem fine. |
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I clearly started renovating this a few years ago and then stopped. Probably should merge these changes, not that I think anyone still uses this library.