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fix encoding string table entries

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This commit is contained in:
Robin Appelman 2017-11-25 00:14:41 +01:00
commit 6d0c81ff30
6 changed files with 107 additions and 11 deletions
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56
src/Parser/StringTableParser.ts
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@ -61,7 +61,7 @@ export function parseStringTableEntries(
existingEntry.extraData = userData;
}
if (value) {
if (typeof value !== 'undefined') {
existingEntry.text = value;
}
entries[entryIndex] = existingEntry;
@ -97,9 +97,11 @@ export function guessStringTableEntryLength(table: StringTable, entries: StringT
export function encodeStringTableEntries(stream: BitStream, table: StringTable, entries: StringTableEntry[], oldEntries: StringTableEntry[] = []) {
const entryBits = logBase2(table.maxEntries);
const lastIndex = -1;
let lastIndex = -1;
const history: StringTableEntry[] = [];
for (let i = 0; i < entries.length; i++) {
if (entries[i]) {
const entry = entries[i];
if (i !== (lastIndex + 1)) {
stream.writeBoolean(false);
@ -107,17 +109,26 @@ export function encodeStringTableEntries(stream: BitStream, table: StringTable,
} else {
stream.writeBoolean(true);
}
lastIndex = i;
if (typeof entry.text !== 'undefined' && !(oldEntries[i] && entry.text === oldEntries[i].text)) {
stream.writeBoolean(true);
// we don't encode substring optimizations
stream.writeBoolean(false);
stream.writeASCIIString(entry.text);
const {index, count} = getBestPreviousString(history, entry.text);
if (index !== -1) {
stream.writeBoolean(true);
stream.writeBits(index, 5);
stream.writeBits(count, 5);
stream.writeASCIIString(entry.text.substr(count));
} else {
stream.writeBoolean(false);
stream.writeASCIIString(entry.text);
}
} else {
stream.writeBoolean(false);
}
if (entry.extraData) {
stream.writeBoolean(true);
@ -133,6 +144,41 @@ export function encodeStringTableEntries(stream: BitStream, table: StringTable,
} else {
stream.writeBoolean(false);
}
history.push(entry);
if (history.length > 32) {
history.shift();
}
}
}
}
function getBestPreviousString(history: StringTableEntry[], newString: string): {index: number, count: number} {
let bestIndex = -1;
let bestCount = 0;
for (let i = 0; i < history.length; i++) {
const prev = history[i].text;
const similar = countSimilarCharacters(prev, newString);
if (similar >= 3 && similar > bestCount) {
bestCount = similar;
bestIndex = i;
}
}
return {
index: bestIndex,
count: bestCount
};
}
const maxSimLength = 1 << 5;
function countSimilarCharacters(a: string, b: string) {
const length = Math.min(a.length, b.length, maxSimLength);
for (let i = 0; i < length; i++) {
if (a[i] !== b[i]) {
return i;
}
}
return Math.min(length, maxSimLength - 1);
}