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Shorter encoding for numbers (breaking change) #9

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Shorter encoding for numbers (breaking change) #9

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30d4c5d
also include smallish integers in tests
dominictarr May 12, 2018
26790f2
use a single character appended to negative numbers, not lots of zeros
dominictarr May 12, 2018
7cf68fc
clearer code
dominictarr May 12, 2018
db35591
no longer necessary to append . to numbers
dominictarr May 17, 2018
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9 changes: 6 additions & 3 deletions codec/number.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@
// We endpad mantissa with enough zero to exceed mantissa precision.
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this comment is for the old code...

// Then negative numbers' mantissa and exponent are flipped (nines' complement)

var END = '_'

exports.encode = function (number) {
if (isNaN(number)) { return "DaN"; }
if (number === 0) { return "FE 0M0"; }
Expand All @@ -14,8 +16,8 @@ exports.encode = function (number) {

var splitScientificNotation = number.toExponential().split('e');
var exponent = Number(splitScientificNotation[1]) + 500;
var mantissa = splitScientificNotation[0] + (splitScientificNotation[0].indexOf('.') === -1 ? '.' : '') + '0'.repeat(20);
var encoded = 'E' + padStart(String(exponent), 3) + 'M' + String(mantissa);
var mantissa = splitScientificNotation[0]
var encoded = 'E' + padStart(String(exponent), 3) + 'M' + String(mantissa) + (number > 0 ? '' : END)
if (number > 0) {
return 'F' + encoded;
} else {
Expand All @@ -30,7 +32,7 @@ exports.decode = function (encoded) {

var isNegative = encoded[0] === 'D';
var splitEncoded = (isNegative ? flip(encoded) : encoded).slice(2).split('M');
return Number((isNegative ? '-':'') + splitEncoded[1] + 'e' + String(Number(splitEncoded[0])-500));
return Number((isNegative ? '-':'') + splitEncoded[1].replace(END,'') + 'e' + String(Number(splitEncoded[0])-500));
}

function flip(number) {
Expand All @@ -49,3 +51,4 @@ function flip(number) {
function padStart (str, count) {
return (' ').repeat(count - str.length).substr(0,count) + str;
};

5 changes: 4 additions & 1 deletion test/bench.js
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ var randArray = function (opt, depth) {
if (opt.depth != 0 && Math.random() < Math.max(0, opt.depth-depth)/opt.depth) {
array.push(randArray(opt, depth + 1));
} else {
var dice = Math.floor(Math.random() * 5)
var dice = Math.floor(Math.random() * 6)
if(dice === 0) {
array.push(randString())
}
Expand All @@ -33,6 +33,9 @@ var randArray = function (opt, depth) {
if(dice === 4) {
array.push((Math.random()*2 - 1)*1e10);
}
if(dice === 5) {
array.push(~~(Math.random()*1000))
}
}
}
return array;
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