a bit optimize four-digit chunks in integer formatting

[chirizxc]

GodBolt

Number of asm instructions has decreased (78 -> 59)

The current upstream version contains:

movabs  rax, 9999999999999999
cmp     rsi, rax
ja      .LBB0_2

(if n > 9_999_999_999_999_999 -> go to panic)

But this function isn't part of the public API, so I suppose we can use assert_unchecked(n < 10_000_000_000_000_000);

Similarly, write_quad has been moved to a separate fn to reduce duplication slightly

[rustbot]

Some changes occurred in integer formatting

cc @tgross35

[rustbot]

r? @clarfonthey

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[clarfonthey]

Haven't reviewed the code yet, but have you actually benchmarked this other than checking the generated assembly? Because number of instructions isn't really a metric we care about, just speed; we have optimize_for_size separately for that.

[chirizxc]

Haven't reviewed the code yet, but have you actually benchmarked this other than checking the generated assembly? Because number of instructions isn't really a metric we care about, just speed; we have optimize_for_size separately for that.

Yes, I'll send results a little later