Ruby

[ruby/strscan] [JRuby] Optimize scan(): Remove duplicate if (restLen() < patternsize()) return context.nil; checks in
!headonly.
(https://github.com/ruby/strscan/pull/110)

• before: #109

Why?¶

https://github.com/ruby/strscan/blob/d31274f41b7c1e28f23d58cf7bfea03baa818cb7/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java#L371-L373

This means the following :

if (str.size() - curr < pattern.size()) return context.nil;

A similar check is made within StringSupport#index() within
!headonly.

https://github.com/jruby/jruby/blob/be7815ec02356a58891c8727bb448f0c6a826d96/core/src/main/java/org/jruby/util/StringSupport.java#L1706-L1720

 public static int index(ByteList source, ByteList other, int offset, Encoding enc) { int sourceLen = source.realSize(); int sourceBegin = source.begin(); int otherLen = other.realSize(); if (otherLen == 0) return offset; if (sourceLen - offset < otherLen) return -1; 

• source = strBL
• other = patternBL
• offset = strBeg + curr

This means the following :
if (strBL.realSize() - (strBeg + curr) < patternBL.realSize()) return -1;

Both checks are the same.

Benchmark¶

It shows String as a pattern is 2.40x faster than Regexp as a pattern.

$ benchmark-driver benchmark/check_until.yaml Warming up -------------------------------------- regexp 7.613M i/s - 7.593M times in 0.997350s (131.35ns/i) regexp_var 7.793M i/s - 7.772M times in 0.997364s (128.32ns/i) string 13.222M i/s - 13.199M times in 0.998297s (75.63ns/i) string_var 15.283M i/s - 15.216M times in 0.995667s (65.43ns/i) Calculating ------------------------------------- regexp 10.003M i/s - 22.840M times in 2.283361s (99.97ns/i) regexp_var 9.991M i/s - 23.378M times in 2.340019s (100.09ns/i) string 23.454M i/s - 39.666M times in 1.691221s (42.64ns/i) string_var 23.998M i/s - 45.848M times in 1.910447s (41.67ns/i) Comparison: string_var: 23998466.3 i/s string: 23453777.5 i/s - 1.02x slower regexp: 10002809.4 i/s - 2.40x slower regexp_var: 9990580.1 i/s - 2.40x slower 

https://github.com/ruby/strscan/commit/843e931d13