parser: Use a lookup table for Delimiter::from_byte. #358
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r? @tiaanl |
emilio
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@emilio Did you measure the performance of this change somewhere? |
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Built a benchmark for this because I had some time. Before: After: |
tiaanl
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Sep 11, 2023
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I was a bit skeptical about this one. It was either a few conditional jump instructions or a few memory accesses (the buffer doesn't fit fully into a cache line) and I was betting the memory accesses would take longer.
Benchmark numbers look like a good improvement.
src/parser.rs
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| @@ -313,16 +313,22 @@ impl Delimiters { | |||
| } | |||
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| #[inline] | |||
| fn from_byte(byte: Option<u8>) -> Delimiters { | |||
| pub(crate) fn from_byte(byte: Option<u8>) -> Delimiters { | |||
| const TABLE: [Delimiters; 255] = { | |||
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You want [Delimiters; 256] here. Leaving off the last option will generate code that checks for bounds and panics.
src/tests.rs
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| fn delimiter_from_byte(b: &mut Bencher) { | ||
| b.iter(|| { | ||
| for _ in 0..1000 { | ||
| for i in 0..255 { |
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Updated, thanks for the review @tiaanl! |
tiaanl
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Sep 11, 2023
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It's faster.