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fix index-leaf non-overflow payload size calculation #9

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fix index-leaf non-overflow payload size calculation #9

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11 changes: 10 additions & 1 deletion src/parser/index-leaf.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,10 @@ export function parseIndexLeafPage(
const { data } = page;
const view = new DataView(data.buffer, data.byteOffset, data.byteLength);

// (see https://www.sqlite.org/fileformat.html#b_tree_pages for more details)
// > Let X be ((U-12)*64/255)-23.
// > Let M be ((U-12)*32/255)-23 and let K be M+((P-M)%(U-4)).

// Calcualte max and min local size to determine overflow
const usableSize = header.pageSize - header.reservedSpace;
const maxLocal = Math.floor(((usableSize - 12) * 64) / 255 - 23);
Expand All @@ -25,11 +29,16 @@ export function parseIndexLeafPage(
let localPayloadSize = payloadSize;
let overflow = false;
cursor += payloadSizeBytes;


// > If the payload size P is less than or equal to X then the entire payload is stored on the b-tree page.
// Determine if it is overflow
if (payloadSize > maxLocal) {
// > If P is greater than X then the number of bytes stored on the index b-tree page is K if K is less than or equal to X or M otherwise.
localPayloadSize =
minLocal + ((payloadSize - minLocal) % (usableSize - 4));
if (localPayloadSize > maxLocal) {
localPayloadSize = minLocal;
}
overflow = true;
}

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