FindSubstring<&[u8]>: make use of memchr::memmem

[homersimpsons]

I guess that #565 could be closed with this one.

memchr MSRV is rust 1.41.1 so it should be okay.

FTR I did run criterion before and after the change

Gnuplot not found, using plotters backend
arithmetic              time:   [324.31 ns 326.60 ns 329.47 ns]                       
                        change: [-10.858% -8.9005% -6.6184%] (p = 0.00 < 0.05)
                        Performance has improved.

Gnuplot not found, using plotters backend
http/parse/291          time:   [549.57 ns 553.83 ns 559.13 ns]                            
                        thrpt:  [496.34 MiB/s 501.09 MiB/s 504.97 MiB/s]
                 change:
                        time:   [-3.8074% +0.3270% +4.5768%] (p = 0.89 > 0.05)
                        thrpt:  [-4.3765% -0.3259% +3.9581%]
                        No change in performance detected.

Gnuplot not found, using plotters backend
ini/parse/110           time:   [787.46 ns 792.56 ns 798.07 ns]                           
                        thrpt:  [131.45 MiB/s 132.36 MiB/s 133.22 MiB/s]
                 change:
                        time:   [+22.871% +26.582% +29.885%] (p = 0.00 < 0.05)
                        thrpt:  [-23.009% -21.000% -18.614%]
                        Performance has regressed.

ini keys and values/parse/45                                                                            
                        time:   [71.192 ns 71.775 ns 72.519 ns]
                        thrpt:  [591.78 MiB/s 597.92 MiB/s 602.81 MiB/s]
                 change:
                        time:   [-0.5977% +1.4548% +3.3841%] (p = 0.15 > 0.05)
                        thrpt:  [-3.2733% -1.4340% +0.6013%]
                        No change in performance detected.

ini key value/parse/18  time:   [42.604 ns 42.760 ns 42.921 ns]                                    
                        thrpt:  [399.95 MiB/s 401.45 MiB/s 402.92 MiB/s]
                 change:
                        time:   [-0.8172% +1.9369% +5.2980%] (p = 0.22 > 0.05)
                        thrpt:  [-5.0314% -1.9001% +0.8239%]
                        No change in performance detected.

Gnuplot not found, using plotters backend
ini str/parse/109       time:   [600.73 ns 603.32 ns 606.57 ns]                               
                        thrpt:  [171.37 MiB/s 172.30 MiB/s 173.04 MiB/s]
                 change:
                        time:   [-2.5620% -0.3528% +1.6800%] (p = 0.76 > 0.05)
                        thrpt:  [-1.6523% +0.3541% +2.6294%]
                        No change in performance detected.

Gnuplot not found, using plotters backend
json                    time:   [1.4783 us 1.4887 us 1.5011 us]                  
                        change: [-2.8551% -0.7999% +1.1989%] (p = 0.46 > 0.05)
                        No change in performance detected.

recognize_float_bytes result: Ok(([], [45, 49, 46, 50, 51, 52, 69, 45, 49, 50]))
recognize float bytes   time:   [2.8242 ns 2.8338 ns 2.8450 ns]                                   
                        change: [-1.3723% +0.5253% +2.3393%] (p = 0.60 > 0.05)
                        No change in performance detected.

recognize_float_str result: Ok(("", "-1.234E-12"))
recognize float str     time:   [31.359 ns 31.962 ns 32.774 ns]                                 
                        change: [+12.350% +20.029% +27.497%] (p = 0.00 < 0.05)
                        Performance has regressed.

float_bytes result: Ok(([], -0.000000000001234))
float bytes             time:   [14.015 ns 14.120 ns 14.236 ns]                         
                        change: [-3.7928% -1.5161% +0.7351%] (p = 0.21 > 0.05)
                        No change in performance detected.

std_float_bytes result: Ok(([], -0.000000000001234))
std_float bytes         time:   [43.579 ns 43.740 ns 43.924 ns]                             
                        change: [-2.2323% -0.1400% +2.2061%] (p = 0.90 > 0.05)
                        No change in performance detected.

float_str result: Ok(("", -0.000000000001234))
float str               time:   [15.227 ns 15.304 ns 15.394 ns]                       
                        change: [-2.2072% +0.1313% +2.3043%] (p = 0.91 > 0.05)
                        No change in performance detected.

Gnuplot not found, using plotters backend
number                  time:   [1.0228 ns 1.0317 ns 1.0397 ns]                    
                        change: [+9.4588% +10.853% +12.215%] (p = 0.00 < 0.05)
                        Performance has regressed.

[homersimpsons]

Note: I just force-pushed to retry CI, I could not rerun as "[the] workflow file may be broken."

[coveralls]

Coverage decreased (-2.8%) to 81.145% when pulling 3de6704 on homersimpsons:feature/memmem into 4a2f9af on Geal:master.

[Geal]

At this point I'm wondering if using memchr is still the right approach, considering that a lot of parsers looking for a specific token or substring work on very small inputs. Maybe we should compare with a naive implementation

[epage]

My findings are

• memchr is worth it on an opt-in basis
• memmem is not worth it

winnow took the approach of putting memchr behind a simd feature flag and merged this PR in winnow-rs/winnow#86. For every case I've dealt with until now, the simd feature flag was not needed.

Recently, I've been working with Byron on porting gitoxide from nom to winnow (GitoxideLabs/gitoxide#956). Within gitoxide, the use of memchr improves performance by an order of magnitude (from 1.6198 µs to 239.23 ns). Removing memmem further improved performance (no official numbers yet, but more around 170ns)

[epage]

Important to note that for gitoxide, take_until looks for

• space
• newline
• :
• >
• <
• PGP signature begin
• PGP signature end

So its a mix of single-character (the memchr shortcut) and actual substring search

[Geal]

substring search and single character matching could work better as different combinators, they are not meant for the same task, and usually don't happen on the same amount of data. Thank you for taking the time to measure this on a larger codebase

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.47%. Comparing base (83cfb17) to head (8a9579a).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1375   +/-   ##
=======================================
  Coverage   61.47%   61.47%           
=======================================
  Files          24       24           
  Lines        2951     2936   -15     
=======================================
- Hits         1814     1805    -9     
+ Misses       1137     1131    -6     

☔ View full report in Codecov by Sentry.
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[codspeed-hq]

CodSpeed Performance Report

Merging #1375 will not alter performance

_{Comparing homersimpsons:feature/memmem (8a9579a) with main (83cfb17)}

Summary

✅ 24 untouched benchmarks