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49 lines
1.5 KiB
49 lines
1.5 KiB
/**
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* For some purposes, we need to identify rows uniquely across different tables, e.g. when showing
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* data with subtotals. This module implements a simple and reasonably efficient way to combine a
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* tableRef and rowId into a single numeric identifier.
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*/
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// A JS Number can represent integers exactly up to 53 bits. We use some of those bits to
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// represent tableRef (the rowId of the table in _grist_Tables meta table), and the rest to
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// represent rowId in the table. Note that we currently never reuse old ids, so these limits apply
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// to the count of all tables or all rows per table that ever existed, including deleted ones.
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const MAX_TABLES = Math.pow(2, 18); // Up to ~262k tables.
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const MAX_ROWS = Math.pow(2, 35); // Up to ~34 billion rows.
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exports.MAX_TABLES = MAX_TABLES;
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exports.MAX_ROWS = MAX_ROWS;
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/**
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* Given tableRef and rowId, returns a Number combining them.
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*/
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function combine(tableRef, rowId) {
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return tableRef * MAX_ROWS + rowId;
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}
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exports.combine = combine;
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/**
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* Given a combined rowUid, returns the tableRef it represents.
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*/
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function tableRef(rowUid) {
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return Math.floor(rowUid / MAX_ROWS);
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}
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exports.tableRef = tableRef;
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/**
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* Given a combined rowUid, returns the rowId it represents.
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*/
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function rowId(rowUid) {
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return rowUid % MAX_ROWS;
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}
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exports.rowId = rowId;
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/**
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* Returns a human-readable string representation of the rowUid, as "tableRef:rowId".
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*/
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function toString(rowUid) {
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return typeof rowUid === 'number' ? tableRef(rowUid) + ":" + rowId(rowUid) : rowUid;
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}
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exports.toString = toString;
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