Fix an undefined behaviour in os/rand.c#2050
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This is really picky and I almost didn't bother given this is just code lifted from FreeBSD which hasn't changed it in 32 years. https://github.com/lattera/freebsd/blame/401a161083850a9a4ce916f37520c084cff1543b/lib/libc/gen/_rand48.c#L32-L49 However undefined behaviour sanitizer whinges about signed overflows. This happens because the promotion of unsigned short in arithmetic expressions is to signed int, and then multiplying signed ints can overflow from signed to unsigned. Eg: (gdb) p (unsigned short)50000 * (unsigned short)45000 $1 = -2044967296 (gdb) p (unsigned int)50000 * (unsigned int)45000 $2 = 2250000000 Due to 2s complement this makes no difference and casting both to unsigned int before the multiplcation gives you the same bit pattern. It's just the resulting type that differs, as we change that in the assignment anyway. (Note there are similar undefined behaviour issues with md5.c, which I didn't fix.) Signed-off-by: James Bonfield <jkb@sanger.ac.uk>
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This is really picky and I almost didn't bother given this is just code lifted from FreeBSD which hasn't changed it in 32 years.
https://github.com/lattera/freebsd/blame/401a161083850a9a4ce916f37520c084cff1543b/lib/libc/gen/_rand48.c#L32-L49
However undefined behaviour sanitizer whinges about signed overflows. This happens because the promotion of unsigned short in arithmetic expressions is to signed int, and then multiplying signed ints can overflow from signed to unsigned.
Eg:
Due to 2s complement this makes no difference and casting both to unsigned int before the multiplcation gives you the same bit pattern. It's just the resulting type that differs, as we change that in the assignment anyway.
(Note there are similar undefined behaviour issues with md5.c, which I didn't fix.)