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92a43d6904
This PR does two things: - Computes UTF-16 string positions in Rust rather than in JS — eliminating a significant number of traversals of the input string - Applies replacements to the content in ascending order so we only ever move forward through the source string — this lets v8 optimize string concatenation
43 lines
1.1 KiB
TypeScript
43 lines
1.1 KiB
TypeScript
export interface StringChange {
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start: number
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end: number
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replacement: string
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}
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/**
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* Apply the changes to the string such that a change in the length
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* of the string does not break the indexes of the subsequent changes.
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*/
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export function spliceChangesIntoString(str: string, changes: StringChange[]) {
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// If there are no changes, return the original string
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if (!changes[0]) return str
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// Sort all changes in order to make it easier to apply them
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changes.sort((a, b) => {
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return a.end - b.end || a.start - b.start
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})
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// Append original string between each chunk, and then the chunk itself
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// This is sort of a String Builder pattern, thus creating less memory pressure
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let result = ''
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let previous = changes[0]
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result += str.slice(0, previous.start)
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result += previous.replacement
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for (let i = 1; i < changes.length; ++i) {
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let change = changes[i]
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result += str.slice(previous.end, change.start)
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result += change.replacement
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previous = change
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}
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// Add leftover string from last chunk to end
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result += str.slice(previous.end)
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return result
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}
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