Implement unsigned encoding/decoding

Author: jridgewell

packages/sourcemap-codec/src/sourcemap-codec.ts

@@ -1,4 +1,12 @@
-import { comma, decodeInteger, encodeInteger, hasMoreVlq, semicolon } from './vlq';
+import {
+  comma,
+  decodeInteger,
+  decodeSign,
+  encodeInteger,
+  encodeSign,
+  hasMoreVlq,
+  semicolon,
+} from './vlq';
 import { StringWriter, StringReader } from './strings';
 
 export {
@@ -36,17 +44,17 @@ export function decode(mappings: string): SourceMapMappings {
     while (reader.pos < semi) {
       let seg: SourceMapSegment;
 
-      genColumn = decodeInteger(reader, genColumn);
+      genColumn += decodeSign(decodeInteger(reader));
       if (genColumn < lastCol) sorted = false;
       lastCol = genColumn;
 
       if (hasMoreVlq(reader, semi)) {
-        sourcesIndex = decodeInteger(reader, sourcesIndex);
-        sourceLine = decodeInteger(reader, sourceLine);
-        sourceColumn = decodeInteger(reader, sourceColumn);
+        sourcesIndex += decodeSign(decodeInteger(reader));
+        sourceLine += decodeSign(decodeInteger(reader));
+        sourceColumn += decodeSign(decodeInteger(reader));
 
         if (hasMoreVlq(reader, semi)) {
-          namesIndex = decodeInteger(reader, namesIndex);
+          namesIndex += decodeSign(decodeInteger(reader));
           seg = [genColumn, sourcesIndex, sourceLine, sourceColumn, namesIndex];
         } else {
           seg = [genColumn, sourcesIndex, sourceLine, sourceColumn];
@@ -95,15 +103,20 @@ export function encode(decoded: Readonly<SourceMapMappings>): string {
       const segment = line[j];
       if (j > 0) writer.write(comma);
 
-      genColumn = encodeInteger(writer, segment[0], genColumn);
+      encodeInteger(writer, encodeSign(segment[0] - genColumn));
+      genColumn = segment[0];
 
       if (segment.length === 1) continue;
-      sourcesIndex = encodeInteger(writer, segment[1], sourcesIndex);
-      sourceLine = encodeInteger(writer, segment[2], sourceLine);
-      sourceColumn = encodeInteger(writer, segment[3], sourceColumn);
+      encodeInteger(writer, encodeSign(segment[1] - sourcesIndex));
+      sourcesIndex = segment[1];
+      encodeInteger(writer, encodeSign(segment[2] - sourceLine));
+      sourceLine = segment[2];
+      encodeInteger(writer, encodeSign(segment[3] - sourceColumn));
+      sourceColumn = segment[3];
 
       if (segment.length === 4) continue;
-      namesIndex = encodeInteger(writer, segment[4], namesIndex);
+      encodeInteger(writer, encodeSign(segment[4] - namesIndex));
+      namesIndex = segment[4];
     }
   }
 

packages/sourcemap-codec/src/vlq.ts

@@ -13,7 +13,7 @@ for (let i = 0; i < chars.length; i++) {
   charToInt[c] = i;
 }
 
-export function decodeInteger(reader: StringReader, relative: number): number {
+export function decodeInteger(reader: StringReader): number {
   let value = 0;
   let shift = 0;
   let integer = 0;
@@ -25,28 +25,24 @@ export function decodeInteger(reader: StringReader, relative: number): number {
     shift += 5;
   } while (integer & 32);
 
-  const shouldNegate = value & 1;
-  value >>>= 1;
-
-  if (shouldNegate) {
-    value = -0x80000000 | -value;
-  }
-
-  return relative + value;
+  return value;
 }
 
-export function encodeInteger(builder: StringWriter, num: number, relative: number): number {
-  let delta = num - relative;
+export function decodeSign(num: number): number {
+  return num & 1 ? -0x80000000 | -(num >>> 1) : num >>> 1;
+}
 
-  delta = delta < 0 ? (-delta << 1) | 1 : delta << 1;
+export function encodeInteger(builder: StringWriter, num: number) {
   do {
-    let clamped = delta & 0b011111;
-    delta >>>= 5;
-    if (delta > 0) clamped |= 0b100000;
+    let clamped = num & 0b011111;
+    num >>>= 5;
+    if (num > 0) clamped |= 0b100000;
     builder.write(intToChar[clamped]);
-  } while (delta > 0);
+  } while (num > 0);
+}
 
-  return num;
+export function encodeSign(num: number): number {
+  return num < 0 ? (-num << 1) | 1 : num << 1;
 }
 
 export function hasMoreVlq(reader: StringReader, max: number) {