perf(string): better slice by bytes

Avoid create Buffer, use character index.
kevinhwang91 · Oct 24, 2022 · be402d8 · be402d8
1 parent 3b0bbda
commit be402d8
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Showing 3 changed files with 13 additions and 12 deletions.
diff --git a/src/__tests__/modules/util.test.ts b/src/__tests__/modules/util.test.ts
@@ -310,6 +310,12 @@ describe('strings', () => {
     expect(strings.utf8_code2len(65537)).toBe(4)
   })
 
+  it('should slice content by bytes', async () => {
+    expect(strings.byteSlice('你', 0, 1)).toBe('你')
+    expect(strings.byteSlice('你', 0, 3)).toBe('你')
+    expect(strings.byteSlice('abc你', 3, 6)).toBe('你')
+  })
+
   it('should get case', async () => {
     expect(strings.getCase('a'.charCodeAt(0))).toBe(1)
     expect(strings.getCase('A'.charCodeAt(0))).toBe(2)

diff --git a/src/completion/index.ts b/src/completion/index.ts
@@ -176,7 +176,7 @@ export class Completion implements Disposable {
     option.filetype = doc.filetype
     logger.debug('trigger completion with', option)
     this.stop(true)
-    this.pretext = option.line.slice(0, characterIndex(option.line, option.colnr - 1))
+    this.pretext = byteSlice(option.line, 0, option.colnr - 1)
     sourceList = sourceList ?? getSources(option)
     if (isFalsyOrEmpty(sourceList)) return
     let complete = this.complete = new Complete(

diff --git a/src/util/string.ts b/src/util/string.ts
@@ -106,25 +106,20 @@ export function characterIndex(content: string, byteIndex: number): number {
   return characterIndex
 }
 
-/**
- * No need to create Buffer
- */
-export function utf8ByteSlice(content: string, start: number, end: number) {
-  let si = characterIndex(content, start)
-  let ei = characterIndex(content, end)
-  return content.slice(si, ei)
-}
-
 export function utf8_code2len(code: number): number {
   if (code < UTF8_2BYTES_START) return 1
   if (code < UTF8_3BYTES_START) return 2
   if (code < UTF8_4BYTES_START) return 3
   return 4
 }
 
+/**
+ * No need to create Buffer
+ */
 export function byteSlice(content: string, start: number, end?: number): string {
-  let buf = Buffer.from(content, 'utf8')
-  return buf.slice(start, end).toString('utf8')
+  let si = characterIndex(content, start)
+  let ei = characterIndex(content, end)
+  return content.slice(si, ei)
 }
 
 export function isWord(character: string): boolean {