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Positional Population Count for Go

License: BSD 2-Clause "Simplified" License

Go 27.95% Assembly 72.05%

pospop's Issues

bit matrix transpositions slows down counting

Hi Robert,

Thanks for persisting optimizing this great package.

I found that bit matrix transpositions slows down counting (100K buffer and others) since d24d616b (Add new count8 variant using bit matrix transpositions). I know you're creating a general framework to port to other platform, a little performance reduction may be tolerated.

I add some tests with few bytes, which I use in my cases.

Current version: d6e39e5

BenchmarkCount8/avx2/32-16              74935256                15.5 ns/op      2066.51 MB/s
BenchmarkCount8/avx2/64-16              55956423                20.3 ns/op      3153.58 MB/s
BenchmarkCount8/avx2/128-16             37906530                29.8 ns/op      4302.12 MB/s
BenchmarkCount8/avx2/256-16             24502731                50.8 ns/op      5038.58 MB/s
BenchmarkCount8/avx2/512-16             31988312                37.8 ns/op      13560.77 MB/s
BenchmarkCount8/avx2/1000-16            20510130                61.9 ns/op      16148.71 MB/s
BenchmarkCount8/avx2/10000-16            2245747               524 ns/op        19087.36 MB/s
BenchmarkCount8/avx2/100000-16            248845              4595 ns/op        21761.87 MB/s

Starting using bit matrix transpositions: 41dbbc5 (speedup after d24d616b)

BenchmarkCount8/avx2/32-16              100472971               13.2 ns/op      2431.84 MB/s
BenchmarkCount8/avx2/64-16              66744648                17.9 ns/op      3568.20 MB/s
BenchmarkCount8/avx2/128-16             42810946                28.3 ns/op      4530.39 MB/s
BenchmarkCount8/avx2/256-16             20535319                56.7 ns/op      4516.74 MB/s
BenchmarkCount8/avx2/512-16             33010789                37.1 ns/op      13811.14 MB/s
BenchmarkCount8/avx2/1000-16            21271256                56.3 ns/op      17774.12 MB/s
BenchmarkCount8/avx2/10000-16            2517070               447 ns/op        22377.79 MB/s
BenchmarkCount8/avx2/100000-16            296733              4059 ns/op        24637.18 MB/s

Old but fast way:
677120e

BenchmarkCount8/avx2/32-16              181525946                7.16 ns/op     4466.72 MB/s
BenchmarkCount8/avx2/64-16              112528216               10.5 ns/op      6069.95 MB/s
BenchmarkCount8/avx2/128-16             63801217                18.7 ns/op      6836.36 MB/s
BenchmarkCount8/avx2/256-16             40247318                29.1 ns/op      8795.27 MB/s
BenchmarkCount8/avx2/512-16             38962676                28.7 ns/op      17869.65 MB/s
BenchmarkCount8/avx2/1000-16            20517376                57.8 ns/op      17289.99 MB/s
BenchmarkCount8/avx2/10000-16            2644093               432 ns/op        23135.55 MB/s
BenchmarkCount8/avx2/100000-16            295675              3913 ns/op        25554.00 MB/s

Eliminate temporary variables from the CSA operation

Consider:

// B:A = A+B+C
#define CSA(A, B, C, D) \
	MOVOA A, D \
	PAND B, D \
	PXOR B, A \
	MOVOA A, B \
	PAND C, B \
	PXOR C, A \
	POR D, B

// B:A = A+B+C
#define CSA(A, B, C) \
	PXOR C, B \ 
	PXOR A, C \
	PXOR B, A \
	POR  C, B \
	PXOR A, B

The C input must be ready 1 cycle earlier.

This is mainly for SSE2 platforms. AVX2/NEON instructions have non-destructive 3-operand forms.

Some architectures have "free" "mov elimination" which makes this change hard to benchmark.

IIRC, a problem I was having before was about how the compiler was merging a load with an xor instruction...

xor r1, [mem]

load r2, [mem]
xor r1, r2

Not sure if this would be an issue with GoLang Assembly.

======

This issue is not important, feel free to close this out, just one of my pet projects.

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