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skip subalphabet encoding when no subalphabet fits the segment

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ccmdi
2026-08-14 11:42:17 -04:00
committed by p2r3
parent a79bd4a862
commit 0b3aa5633f
1 changed files with 10 additions and 3 deletions
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compress.js
+10 -3
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@@ -245,9 +245,9 @@ export function compress (input, alphabet) {
queryParamIndex ++; queryParamIndex ++;
} }
// Look for smallest subalphabet that fits this path segment // Look for smallest subalphabet that fits this path segment
let subalphabetIndex = subalphabets.length - 1; let subalphabetIndex = -1;
let subalphabet = subalphabets[subalphabetIndex]; let subalphabet = null;
for (let i = 0; i < subalphabets.length - 1; i ++) { for (let i = 0; i < subalphabets.length; i ++) {
if (!Array.from(segment.value).some(c => !subalphabets[i].includes(c))) { if (!Array.from(segment.value).some(c => !subalphabets[i].includes(c))) {
subalphabet = subalphabets[i]; subalphabet = subalphabets[i];
subalphabetIndex = i; subalphabetIndex = i;
@@ -283,6 +283,13 @@ export function compress (input, alphabet) {
// Encode segment variant as 0 // Encode segment variant as 0
// (We're adding +1 here to introduce 0 as a special value indicating Huffman) // (We're adding +1 here to introduce 0 as a special value indicating Huffman)
huffmanNumber *= BigInt(subalphabets.length + 1); huffmanNumber *= BigInt(subalphabets.length + 1);
// If no subalphabet fits this segment, Huffman is the only option.
// Encoding a character missing from the subalphabet would produce the
// value 0, which the decoder treats as the end of the segment.
if (!subalphabet) {
number = huffmanNumber;
continue;
}
// Compute number after encoding with chosen subalphabet // Compute number after encoding with chosen subalphabet
const subalphabetLength = BigInt(subalphabet.length + 1); const subalphabetLength = BigInt(subalphabet.length + 1);
let subalphabetNumber = firstIteration ? number : number * subalphabetLength; let subalphabetNumber = firstIteration ? number : number * subalphabetLength;