Luke Champine
62 lines
2.3 KiB
Markdown
62 lines
2.3 KiB
Markdown
fastxor
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-----
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[](https://godoc.org/github.com/lukechampine/fastxor)
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[](https://goreportcard.com/report/github.com/lukechampine/fastxor)
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```
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go get github.com/lukechampine/fastxor
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```
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Is there a gaping hole in your heart that can only be filled by xor'ing byte
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streams at 60GB/s? If so, you've come to the right place.
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`fastxor` is exactly what it sounds like: a package that xors bytes as fast
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as your CPU is capable of. For best results, use a CPU that supports a SIMD
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instruction set like SSE or AVX. On other architectures, performance is much
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less impressive, but still faster than a naive byte-wise loop.
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I wrote this package to try my hand at writing Go assembly, so please scrutinize
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my code and let me know how I could make it faster or cleaner!
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# Benchmarks
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```
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AVX:
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BenchmarkBytes/16-4 200000000 6.20 ns/op 2579.65 MB/s
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BenchmarkBytes/1024-4 100000000 15.5 ns/op 66089.39 MB/s
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BenchmarkBytes/65k-4 2000000 974 ns/op 67217.99 MB/s
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SSE:
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BenchmarkBytes/16-4 200000000 6.31 ns/op 2536.64 MB/s
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BenchmarkBytes/1024-4 50000000 27.2 ns/op 37609.69 MB/s
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BenchmarkBytes/65k-4 1000000 2009 ns/op 32619.21 MB/s
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Word-wise:
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BenchmarkBytes/16-4 200000000 7.37 ns/op 2170.17 MB/s
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BenchmarkBytes/1024-4 20000000 89.4 ns/op 11455.33 MB/s
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BenchmarkBytes/65k-4 300000 4963 ns/op 13203.25 MB/s
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Byte-wise:
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BenchmarkBytes/16-4 100000000 12.7 ns/op 1263.77 MB/s
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BenchmarkBytes/1024-4 2000000 610 ns/op 1677.18 MB/s
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BenchmarkBytes/65k-4 50000 38906 ns/op 1684.45 MB/s
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```
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Conclusions: `fastxor` is 2-40 times faster than a naive `for` loop. AVX is
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roughly twice as fast as SSE, which is unsurprising since it can operate on
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twice as many bits per cycle. Lastly, for very small slices, the cost of the
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function call starts to outweigh the benefit of AVX/SSE (the Go compiler never
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inlines handwritten asm). If you need to xor exactly 16 bytes (common in block
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ciphers), the specialized `Block` function is about 6 times faster than the
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more generic `Bytes`:
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```
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BenchmarkBlock-4 2000000000 1.18 ns/op 13546.30 MB/s
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```
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