faster hex to decimal conversion

[ghost]

As part of some ongoing performance improvements we identified hex2dec as a piece of code that gets called a lot and could be improved. This doesn't move the needle much on total time for bulk imports, but this patch should improve hex2dec perf about 4-fold from 58ms to 14ms:

> var convert = require('base-convertor'); var start = Date.now(); for (var i = 0; i < 1000; i++) convert('abc123','0123456789abcdef','0123456789'); Date.now() - start
58
> function newconvert (s) { var d=''; for (var i=s.length-5; i>-5; i-=5) d = parseInt(s.slice(Math.max(0,i),i+5),16)+d; return d }
> var start = Date.now(); for (var i = 0; i < 1000; i++) newconvert('abc123'); Date.now() - start 
14

[codecov-io]

Codecov Report

Merging #33 into master will increase coverage by 0.07%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   86.99%   87.07%   +0.07%     
==========================================
  Files          29       29              
  Lines         723      727       +4     
==========================================
+ Hits          629      633       +4     
  Misses         94       94

Impacted Files	Coverage Δ
lib/util.js	97.56% <100%> (+0.12%)	:arrow_up:
api/put_changes.js	96% <0%> (+0.16%)	:arrow_up:

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[hackergrrl]

I was curious if using Node's built-in parseInt and toString() functions would be any faster:

function another_hex2dec (hex) {
  return parseInt(hex, 16).toString(10)
}

I benched it against your new algorithm and the old one:

old_hex2dec:     15906ms
new_hex2dec:     1632ms
another_hex2dec: 1467ms

It's a small difference, but I like the higher readability.

[okdistribute]

Any thoughts on merging this @noffle ?

[hackergrrl]

@okdistribute I think using parseInt(hex, 16).toString(10) would be faster, according to my benchmark above.

[okdistribute]

@noffle okay cool, if you think this is critical perhaps we could update the code to do that or merge as is -- since both of these are an order of magnitude better than the old hex2dec.

[hackergrrl]

6bbec31c9213436aaf770b47091d9b9e83b8217d