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Feature #17115

Updated by sawa (Tsuyoshi Sawada) 11 months ago

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

 `casecmp?` is a 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, unlike because contrary to the others, others it is sensitive tries to be correct in regards to unicode case folding. 

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

 This patch checks check if both strings use a single byte encoding, and if so then does do a simple iterative comparison with `TOLOWER()`. 

 This makes `casecmp?` slightly 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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