bmatch.go

bmatch is faster fixed pattern search for Go.

Go provides different search mechanisms to find the indices of a fixed string or byte pattern, that are backed by different search algorithms:

• strings.Index switches by the pattern length
  • 1: generic assembler function strings•IndexByte(..) (i.e. for OSX/darwin see /usr/local/go/src/runtime/asm_amd64.s)
  • 1-31: generic assembler function strings•indexShortString(..) (i.e. for OSX/darwin see /usr/local/go/src/runtime/asm_amd64.s)

  • 31 calling a Rabin-Karp search algorithm using a rolling addition hash and use string comparison to prove the result

• strings.Replace for single string replacing invokes a Boyer-Moore search over a string in /usr/local/go/src/strings/search.go implementing a stringFinder type
• bytes.Index using generic assembler code (bytes•IndexByte(..)) to find the index of the first element of the pattern (i.e. for OSX/darwin see /usr/local/go/src/runtime/asm_amd64.s) and then compares the following sequence using another assembler function (Equal(..)).

The before mentioned assembler routines compare each byte of the haystack one by one. See unsafeMEMCHR.go for a faster approach. All but the Boyer-Moore search are relatively slow - even in comparison to python str.find function (implemented in C). bmatch's underlying algorithms outperform all of Go's search functions.

If you installed bmatch before 2016-03-20 it is recommended that you reinstall bmatch as there was a bugfix for "needles at haystack start"

Usage

Install bmatch by the usual

go get github.com/AndreasBriese/bmatch

In your go code use import "github.com/AndreasBriese/bmatch" and apply it on []byte types of the haystack (byte sequence to search in) and needle (pattern to search for).

index, err := bmatch.Index(&haystack, &needle) gives the first (left) index or -1 if not present,

indices, err := bmatch.FindAll(&haystack, &needle) to get an []int array with indices of (overlapping!) occurrences, or

count, err := bmatch.Count(&haystack, &needle) to get the number of (overlapping!) occurences of needle in haystack.

Benchmarks (go test -bench . cpu=1)

 ###############
 bmatch.go
 Haystack: ./theciaworldfactb00571.zip loaded (3013205 bytes)
 Alphabet size: 93
 
 PASS
 BenchmarkM_Bmatch_10_C          	       1	1002289595 ns/op 
 BenchmarkM_BoyerMoore_10_C       	       1	2683892806 ns/op
 BenchmarkM_BytesIndex_10_C       	       1	2630128009 ns/op
 BenchmarkM_Bmatch_30_C           	       2	 528011588 ns/op
 BenchmarkM_BoyerMoore_30_C       	       1	1402345246 ns/op
 BenchmarkM_BytesIndex_30_C       	       1	2654263863 ns/op
 BenchmarkM_Bmatch_1024_C         	      20	 105107250 ns/op
 BenchmarkM_BoyerMoore_1024_C     	       5	 214846485 ns/op
 BenchmarkM_BytesIndex_1024_C     	       1	2592599288 ns/op
 BenchmarkM_Bmatch_30_FI        	      10	 104080809 ns/op
 BenchmarkM_BoyerMoore_30_FI    	       5	 245957698 ns/op
 BenchmarkM_StringsIndex_30_FI  	       3	 392142229 ns/op
 BenchmarkM_BytesIndex_30_FI    	       2	 776670641 ns/op
 BenchmarkM_Bmatch_1024_FI      	      30	  43820654 ns/op
 BenchmarkM_BoyerMoore_1024_FI  	      10	 103821315 ns/op
 BenchmarkM_StringsIndex_1024_FI	       1	1306085958 ns/op
 BenchmarkM_BytesIndex_1024_FI  	       1	1276277951 ns/op

on a MacBookPro 2013 with i7 and 8GB Ram searching for 500 random patterns plus 20 patterns that are not present in the "1995 CIA World Factbook" (~3MB english natural text). Benchmark naming: .._searchFunction_patternMaximumLength_C=count|FI=first left Index

go test will try to download the test corpus from http://archive.org if it is not present in the folder.

License
bmatch.go (C)opyright 2016 Andreas Briese, eduToolbox@Bri-C GmbH, Sarstedt, with MIT license - see the headers in the code in the subfolders of the various search algorithms for details and reference to their predecessors (C-code mostly taken from the SMART tool http://www.dmi.unict.it/~faro/smart/ v.13.02).