bors ffdf18d144 Auto merge of #88788 - falk-hueffner:speedup-int-log10-branchless, r=joshtriplett ... Speedup int log10 branchless This is achieved with a branchless bit-twiddling implementation of the case x < 100_000, and using this as building block. Benchmark on an Intel i7-8700K (Coffee Lake): ``` name old ns/iter new ns/iter diff ns/iter diff % speedup num::int_log::u8_log10_predictable 165 169 4 2.42% x 0.98 num::int_log::u8_log10_random 438 423 -15 -3.42% x 1.04 num::int_log::u8_log10_random_small 438 423 -15 -3.42% x 1.04 num::int_log::u16_log10_predictable 633 417 -216 -34.12% x 1.52 num::int_log::u16_log10_random 908 471 -437 -48.13% x 1.93 num::int_log::u16_log10_random_small 945 471 -474 -50.16% x 2.01 num::int_log::u32_log10_predictable 1,496 1,340 -156 -10.43% x 1.12 num::int_log::u32_log10_random 1,076 873 -203 -18.87% x 1.23 num::int_log::u32_log10_random_small 1,145 874 -271 -23.67% x 1.31 num::int_log::u64_log10_predictable 4,005 3,171 -834 -20.82% x 1.26 num::int_log::u64_log10_random 1,247 1,021 -226 -18.12% x 1.22 num::int_log::u64_log10_random_small 1,265 921 -344 -27.19% x 1.37 num::int_log::u128_log10_predictable 39,667 39,579 -88 -0.22% x 1.00 num::int_log::u128_log10_random 6,456 6,696 240 3.72% x 0.96 num::int_log::u128_log10_random_small 4,108 3,903 -205 -4.99% x 1.05 ``` Benchmark on an M1 Mac Mini: ``` name old ns/iter new ns/iter diff ns/iter diff % speedup num::int_log::u8_log10_predictable 143 130 -13 -9.09% x 1.10 num::int_log::u8_log10_random 375 325 -50 -13.33% x 1.15 num::int_log::u8_log10_random_small 376 325 -51 -13.56% x 1.16 num::int_log::u16_log10_predictable 500 322 -178 -35.60% x 1.55 num::int_log::u16_log10_random 794 405 -389 -48.99% x 1.96 num::int_log::u16_log10_random_small 1,035 405 -630 -60.87% x 2.56 num::int_log::u32_log10_predictable 1,144 894 -250 -21.85% x 1.28 num::int_log::u32_log10_random 832 786 -46 -5.53% x 1.06 num::int_log::u32_log10_random_small 832 787 -45 -5.41% x 1.06 num::int_log::u64_log10_predictable 2,681 2,057 -624 -23.27% x 1.30 num::int_log::u64_log10_random 1,015 806 -209 -20.59% x 1.26 num::int_log::u64_log10_random_small 1,004 795 -209 -20.82% x 1.26 num::int_log::u128_log10_predictable 56,825 56,526 -299 -0.53% x 1.01 num::int_log::u128_log10_random 9,056 8,861 -195 -2.15% x 1.02 num::int_log::u128_log10_random_small 1,528 1,527 -1 -0.07% x 1.00 ``` The 128 bit case remains ridiculously slow because llvm fails to optimize division by a constant 128-bit value to multiplications. This could be worked around but it seems preferable to fix this in llvm. From u32 up, table lookup (like suggested [here](https://github.com/rust-lang/rust/issues/70887#issuecomment-881099813)) is still faster, but requires a hardware `leading_zeros` to be viable, and might clog up the cache.		2021-10-12 03:18:54 +00:00
..
ascii	mv std libs to library/	2020-07-27 19:51:13 -05:00
char	Add two more benchmarks for strictly ASCII and non ASCII cases	2021-02-26 11:42:59 -06:00
hash	mv std libs to library/	2020-07-27 19:51:13 -05:00
num	Cosmetic fixes.	2021-09-09 20:06:46 +02:00
any.rs	mv std libs to library/	2020-07-27 19:51:13 -05:00
ascii.rs	Unify way to flip 6th bit. (Same assembly generated)	2021-02-08 12:21:36 +00:00
fmt.rs	move core::hint::black_box under its own feature gate	2021-04-25 11:08:12 +02:00
iter.rs	Use HTTPS links where possible	2021-06-23 16:26:46 -04:00
lib.rs	Auto merge of #88788 - falk-hueffner:speedup-int-log10-branchless, r=joshtriplett	2021-10-12 03:18:54 +00:00
ops.rs	mv std libs to library/	2020-07-27 19:51:13 -05:00
pattern.rs	mv std libs to library/	2020-07-27 19:51:13 -05:00
slice.rs	add bench	2021-03-18 00:25:20 +01:00
str.rs	benchmark for str.chars().count()	2021-09-11 00:25:41 +02:00