perf: clean up div, cmp

[DaniPopes]

• Remove impossible panics and reduce size of possible panics (div by 0) from div dispatching code to make it more amenable for inlining
• Fix cmp for slices of different lengths; improve comments

[prestwich]

blocked by #461

[codspeed-hq]

CodSpeed Performance Report

Merging #464 will improve performances by ×2.7

_{Comparing DaniPopes:div-cleanups (1939083) with main (20a2367)}

Summary

⚡ 21 improvements
✅ 204 untouched benchmarks

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	add_mod/64	577.8 µs	238.8 µs	×2.4
⚡	div_rem/128/128	1,193.9 µs	973.9 µs	+22.59%
⚡	div_rem/192/192	1.8 ms	1.4 ms	+32.71%
⚡	div_rem/256/256	2 ms	1.6 ms	+27.71%
⚡	div_rem/384/384	2.4 ms	2 ms	+22.38%
⚡	div_rem/512/512	2.8 ms	2.4 ms	+17.85%
⚡	div_rem/64/32	538 µs	201.5 µs	×2.7
⚡	div_rem/64/64	538 µs	201.5 µs	×2.7
⚡	overflowing_pow/128	622.9 µs	534.9 µs	+16.45%
⚡	overflowing_pow/192	1.3 ms	1.1 ms	+15.92%
⚡	overflowing_pow/256	2.2 ms	2 ms	+11.47%
⚡	overflowing_pow/384	5.1 ms	4.5 ms	+13.93%
⚡	overflowing_pow/4096	2.4 ms	1.7 ms	+39.84%
⚡	pow/384	5.4 ms	4.8 ms	+10.72%
⚡	pow/4096	2.8 ms	2.2 ms	+32%
⚡	pow_mod/64	709.2 µs	641.2 µs	+10.61%
⚡	reduce_mod/64	326 µs	159.5 µs	×2
⚡	root/2/64/64	2.1 ms	1.1 ms	+90.54%
⚡	root/3/64/64	2.2 ms	1.2 ms	+86.11%
⚡	root/5/64/64	2.2 ms	1.2 ms	+81.96%
...	...	...	...	...

ℹ️ Only the first 20 benchmarks are displayed. Go to the app to view all benchmarks.