On 1/16/2022 7:08 AM, Mark Dickinson wrote:
Now /that/ I certainly wasn't expecting. I don't see the same effect on
macOS / Clang, whether compiling with --enable-optimizations or not;
this appears to be a GCC innovation. And indeed, as Tim suggested, it
turns out that there's no division instruction present in the loop for
the division-by-10 case - we're doing division via multiplication by the
reciprocal. In Python terms, we're computing `x // 10` as `(x *
0xcccccccccccccccd) >> 67`.
https://stackoverflow.com/questions/41183935/why-does-gcc-use-multiplication-by-a-strange-number-in-implementing-integer-divi
and
https://stackoverflow.com/questions/30790184/perform-integer-division-using-multiplication
have multiple discussions of the technique for machine division
invariant (small) ints and GCC's use thereof (only suppressed with -0s?).
--
Terry Jan Reedy
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