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Feature #17115

Updated by byroot (Jean Boussier) 12 months ago

Patch: https://github.com/ruby/ruby/pull/3369 

 `casecmp?` is kind of a performance trap as it's much slower than using a case insensitive regexp or just `casecmp == 0`. 

 ``` 
 str = "Connection" 
 cmp = "connection" 
 Benchmark.ips do |x| 
   x.report('/\A\z/i.match?') { /\Afoo\Z/i.match?(str) } 
   x.report('casecmp?') { cmp.casecmp?(str) } 
   x.report('casecmp') { cmp.casecmp(str) == 0 } 
   x.compare! 
 end 
 Calculating ------------------------------------- 
       /\A\z/i.match?       11.447M (± 1.3%) i/s -       57.814M in     5.051489s 
             casecmp?        6.197M (± 0.9%) i/s -       31.138M in     5.025252s 
              casecmp       12.753M (± 1.2%) i/s -       64.636M in     5.069195s 

 Comparison: 
              casecmp: 12752791.6 i/s 
       /\A\z/i.match?: 11446996.1 i/s - 1.11x    (± 0.00) slower 
             casecmp?:    6196886.0 i/s - 2.06x    (± 0.00) slower 
 ``` 

 This is because contrary to the others it tries to be correct in regards to unicode case folding. 

 However there are cases where fast case insentive equality check of known ASCII strings is useful. For instance for matching HTTP headers. 

 This patch check if both strings use a single byte encoding, and if so then do a simple iterative comparison with `TOLOWER()`. delegate most of the work to strncasecmp(3) 

 This makes casecmp? sligthly faster than `casecmp == 0` when both strings are ASCII. 

 ``` 
 |                          |compare-ruby|built-ruby| 
 |:-----------------------|-----------:|---------:| 
 |casecmp-1                 |       11.618M|     10.757M| 
 |                          |         1.08x|           -| 
 |casecmp-10                |        1.849M|      1.723M| 
 |                          |         1.07x|           -| 
 |casecmp-100               |      204.490k|    186.798k| 
 |                          |         1.09x|           -| 
 |casecmp-1000              |       20.413k|     20.184k| 
 |                          |         1.01x|           -| 
 |casecmp-nonascii1         |       19.541M|     20.100M| 
 |                          |             -|       1.03x| 
 |casecmp-nonascii10        |       19.489M|     19.914M| 
 |                          |             -|       1.02x| 
 |casecmp-nonascii100       |       19.479M|     20.155M| 
 |                          |             -|       1.03x| 
 |casecmp-nonascii1000      |       19.462M|     20.064M| 
 |                          |             -|       1.03x| 
 |casecmp_p-1               |        2.214M|     12.030M| 
 |                          |             -|       5.43x| 
 |casecmp_p-10              |        1.373M|      2.150M| 
 |                          |             -|       1.57x| 
 |casecmp_p-100             |      249.292k|    231.041k| 
 |                          |         1.08x|           -| 
 |casecmp_p-1000            |       16.173k|     23.592k| 
 |                          |             -|       1.46x| 
 |casecmp_p-nonascii1       |      651.921k|    650.572k| 
 |                          |         1.00x|           -| 
 |casecmp_p-nonascii10      |      108.253k|    109.006k| 
 |                          |             -|       1.01x| 
 |casecmp_p-nonascii100     |       11.749k|     11.889k| 
 |                          |             -|       1.01x| 
 |casecmp_p-nonascii1000    |        1.140k|      1.138k| 
 |   
 ```

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