wc: Assume long lines initially and find EOL with rawmemchr() - #351
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Start processing input by assuming its lines are long (>= 15 characters) and use rawmemchr() instead of checking individual bytes to find EOLs. The average line length in the distribution of linux-7.2.4 is 36 characters. Moving byte-by-byte is grossly suboptimal for long lines. Confirmed experimentally that the 15-character threshold is optimal: github.com/coreutils/pull/347#issuecomment-5653011937
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Also: $ A=$(for i in $(find /etc/ -type f); do file "$i"|grep ': ASCII text$' >/dev/null && cat "$i"; done | wc -l)
$ B=$(for i in $(find /etc/ -type f); do file "$i"|grep ': ASCII text$' >/dev/null && cat "$i"; done | wc -c)
$ echo $A $B $(( (B-A) / A ))
23603 744436 30 |
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Estimate the length of lines in input and choose a method of finding EOLs appropriately to increase performance: memchr() for long lines, manual byte-wise search for short lines. Long-short threshold = 15, experimentally: github.com/coreutils/pull/347#issuecomment-5653011937 Initial guess = long lines, based on Linux sources and /etc: coreutils#351
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Well, now I built coreutils with a simple |
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Start processing input by assuming its lines are long (>= 15 characters) and use
rawmemchr()instead of checking individual bytes to findEOLs. The average line length in the distribution of linux-7.2.4 is 36 characters. Moving byte-by-byte is grossly suboptimal for long lines.Confirmed experimentally that the 15-character threshold is optimal.