fastxor

README

fastxor

go get github.com/lukechampine/fastxor

Is there a gaping hole in your heart that can only be filled by xor'ing byte streams at 60GB/s? If so, you've come to the right place.

fastxor is exactly what it sounds like: a package that xors bytes as fast as your CPU is capable of. For best results, use a CPU that supports a SIMD instruction set like SSE or AVX. On other architectures, performance is much less impressive, but still faster than a naive byte-wise loop.

I wrote this package to try my hand at writing Go assembly, so please scrutinize my code and let me know how I could make it faster or cleaner!

Benchmarks

AVX:

BenchmarkBytes/16-4   	200000000	         6.20 ns/op	 2579.65 MB/s
BenchmarkBytes/1024-4 	100000000	        15.5 ns/op	66089.39 MB/s
BenchmarkBytes/65k-4  	  2000000	       974 ns/op	67217.99 MB/s

SSE:

BenchmarkBytes/16-4   	200000000	         6.31 ns/op	 2536.64 MB/s
BenchmarkBytes/1024-4 	 50000000	        27.2 ns/op	37609.69 MB/s
BenchmarkBytes/65k-4  	  1000000	      2009 ns/op	32619.21 MB/s

Word-wise:

BenchmarkBytes/16-4   	200000000	         7.37 ns/op	 2170.17 MB/s
BenchmarkBytes/1024-4 	 20000000	        89.4 ns/op	11455.33 MB/s
BenchmarkBytes/65k-4  	   300000	      4963 ns/op	13203.25 MB/s

Byte-wise:

BenchmarkBytes/16-4    	100000000	        12.7 ns/op	 1263.77 MB/s
BenchmarkBytes/1024-4  	  2000000	       610 ns/op	 1677.18 MB/s
BenchmarkBytes/65k-4   	    50000	     38906 ns/op	 1684.45 MB/s

Conclusions: fastxor is 2-40 times faster than a naive for loop. AVX is roughly twice as fast as SSE, which is unsurprising since it can operate on twice as many bits per cycle. Lastly, for very small slices, the cost of the function call starts to outweigh the benefit of AVX/SSE (the Go compiler never inlines handwritten asm). If you need to xor exactly 16 bytes (common in block ciphers), the specialized Block function is about 6 times faster than the more generic Bytes:

BenchmarkBlock-4      	2000000000	        1.18 ns/op	13546.30 MB/s

Documentation

Index

• func Block(dst, a, b []byte)
• func Byte(dst, a []byte, b byte) int
• func Bytes(dst, a, b []byte) int

Functions

func Block

func Block(dst, a, b []byte)

Block stores (a xor b) in dst, where a, b, and dst all have length 16.

func Byte

func Byte(dst, a []byte, b byte) int

Byte xors each byte in a with b and stores the result in dst, stopping when the end of either dst or a is reached. It returns the number of bytes xor'd.

func Bytes

func Bytes(dst, a, b []byte) int

Bytes stores (a xor b) in dst, stopping when the end of any slice is reached. It returns the number of bytes xor'd.