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Use binary search to improve getNewlinesBefore/After performance

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This commit is contained in:
Jason 2016-01-19 21:18:06 +08:00
parent 76e3c5227b
commit ed227a6c8a
1 changed files with 23 additions and 52 deletions
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75
packages/babel-generator/src/whitespace.js
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@ -1,18 +1,3 @@
/**
* Returns `i`th number from `base`, continuing from 0 when `max` is reached.
* Useful for shifting `for` loop by a fixed number but going over all items.
*/
function getLookupIndex(i: number, base: number, max: number): number {
i += base;
if (i >= max) {
i -= max;
}
return i;
}
/**
* Get whitespace around tokens.
*/
@ -21,16 +6,6 @@ export default class Whitespace {
constructor(tokens) {
this.tokens = tokens;
this.used = {};
// Profiling this code shows that while generator passes over it, indexes
// returned by `getNewlinesBefore` and `getNewlinesAfter` are always increasing.
// We use this implementation detail for an optimization: instead of always
// starting to look from `this.tokens[0]`, we will start `for` loops from the
// previous successful match. We will enumerate all tokens—but the common
// case will be much faster.
this._lastFoundIndex = 0;
}
/**
@ -42,19 +17,11 @@ export default class Whitespace {
let endToken;
let tokens = this.tokens;
for (let j = 0; j < tokens.length; j++) {
// optimize for forward traversal by shifting for loop index
let i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
let token = tokens[i];
// this is the token this node starts with
if (node.start === token.start) {
startToken = tokens[i - 1];
endToken = token;
this._lastFoundIndex = i;
break;
}
let index = this.findToken(token => token.start - node.start, 0, tokens.length);
if (typeof index === "number") {
while (index && node.start === tokens[index - 1].start) --index;
startToken = tokens[index - 1];
endToken = tokens[index];
}
return this.getNewlinesBetween(startToken, endToken);
@ -69,20 +36,12 @@ export default class Whitespace {
let endToken;
let tokens = this.tokens;
for (let j = 0; j < tokens.length; j++) {
// optimize for forward traversal by shifting for loop index
let i = getLookupIndex(j, this._lastFoundIndex, this.tokens.length);
let token = tokens[i];
// this is the token this node ends with
if (node.end === token.end) {
startToken = token;
endToken = tokens[i + 1];
if (endToken.type.label === ",") endToken = tokens[i + 2];
this._lastFoundIndex = i;
break;
}
let index = this.findToken(token => token.end - node.end, 0, tokens.length);
if (typeof index === "number") {
while (index && node.end === tokens[index - 1].end) --index;
startToken = tokens[index];
endToken = tokens[index + 1];
if (endToken.type.label === ",") endToken = tokens[index + 2];
}
if (endToken && endToken.type.label === "eof") {
@ -98,6 +57,18 @@ export default class Whitespace {
}
}
findToken(test, start, end) {
const middle = (start + end) >>> 1;
const match = test(this.tokens[middle]);
if (match < 0 && end > middle) {
return this.findToken(test, middle + 1, end);
} else if (match > 0 && start < middle) {
return this.findToken(test, start, middle);
} else if (match === 0) {
return middle;
}
}
/**
* Count all the newlines between two tokens.
*/