Volodymyr Gubarkov

Using GAWK coprocess to speed up the script 50x

February 2024

In a need to parse some logs, extract values from it, and convert a value from hex to decimal, I came up with this GAWK script:

match($0, /larger than 15 chars: (.+) actual size is: 19 .+ GUID: (.+),/, arr) {
  print arr[1],arr[2],hex2dec(arr[2])
}

function hex2dec(h,   s,res) {
  s = "echo \"obase=10; ibase=16; " h "\" | bc"
  s | getline res
  close(s)
  return res
}

Note, the conversion hex → dec is done via bc.

Why is that? Well, it appears, that if you do it in native GAWK, you’ll get the incorrect result due to the precision loss:

# correct
$ echo "obase=10; ibase=16; 11000187D6CAA7BD" | bc
1224980781580593085

# incorrect
$ gawk 'BEGIN { print strtonum("0x11000187D6CAA7BD") }'
1224980781580593152

But this appears to be rather slow, because we start a new bc subprocess for each log line.

Fix

Coprocess to the resque!

match($0, /larger than 15 chars: (.+) actual size is: 19 .+ GUID: (.+),/, arr) {
  print arr[1],arr[2],hex2dec(arr[2])
}

BEGIN {
  print "obase=10; ibase=16;" |& "bc"
}

function hex2dec(h,   res) {
  print h |& "bc"
  "bc" |& getline res
  return res
}

Now we start only one bc subprocess–which runs in parallel with our code–and interactively write hexes to it and read decimals back.

Result

Before	After
34.260 s	0.608 s

This is 50x + speedup! 🥳

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If you noticed a typo or have other feedback, please email me at xonixx@gmail.com