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Speed up parse ~15% by reusing the last line in Input#fromOffset #2173

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Speed up parse ~15% by reusing the last line in Input#fromOffset #2173

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39 changes: 21 additions & 18 deletions lib/input.js
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Original file line number Diff line number Diff line change
Expand Up @@ -10,19 +10,19 @@ let PreviousMap = require('./previous-map')
let terminalHighlight = require('./terminal-highlight')

let lineToIndexCache = Symbol('lineToIndexCache')
let lastLineCache = Symbol('lastLineCache')

let sourceMapAvailable = Boolean(SourceMapConsumer && SourceMapGenerator)
let pathAvailable = Boolean(resolve && isAbsolute)

function getLineToIndex(input) {
if (input[lineToIndexCache]) return input[lineToIndexCache]
let lines = input.css.split('\n')
let lineToIndex = new Array(lines.length)
let prevIndex = 0

for (let i = 0, l = lines.length; i < l; i++) {
lineToIndex[i] = prevIndex
prevIndex += lines[i].length + 1
let css = input.css
let lineToIndex = [0]
let index = css.indexOf('\n')
while (index !== -1) {
lineToIndex.push(index + 1)
index = css.indexOf('\n', index + 1)
}

input[lineToIndexCache] = lineToIndex
Expand Down Expand Up @@ -169,26 +169,29 @@ class Input {

fromOffset(offset) {
let lineToIndex = getLineToIndex(this)
let lastLine = lineToIndex[lineToIndex.length - 1]

let min = 0
if (offset >= lastLine) {
min = lineToIndex.length - 1
} else {
let max = lineToIndex.length - 2
let lastLine = lineToIndex.length - 1

// Parser asks for positions in order, so the answer is usually
// the line from the previous call or the next one
let min = this[lastLineCache] || 0
if (offset < lineToIndex[min]) {
min = 0
} else if (min < lastLine && offset >= lineToIndex[min + 1]) {
min += 1
}
if (min < lastLine && offset >= lineToIndex[min + 1]) {
let max = lastLine
let mid
while (min < max) {
mid = min + ((max - min) >> 1)
mid = min + ((max - min + 1) >> 1)
if (offset < lineToIndex[mid]) {
max = mid - 1
} else if (offset >= lineToIndex[mid + 1]) {
min = mid + 1
} else {
min = mid
break
}
}
}
this[lastLineCache] = min
return {
col: offset - lineToIndex[min] + 1,
line: min + 1
Expand Down
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