mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-03 07:54:40 +08:00
Chris Tate
1917d1aa00
The dense path of an element read that may be undefined (the `%arr.idxOr` reads behind `a[i]` as `T | undefined`, the store `a[x] = a[y]!`, and the element reads of the lowered array methods) tested the index against the capacity, then against the hole-free prefix (`filled`), and only above the prefix against the length and the slot's state. `filled` is at most the length and the capacity (scr_array.h), so an index below it needs no other test: the read now tests `filled` first and takes the value path on that test alone. Above the prefix it tests the capacity, the length and the state as before. A double index first branches to the runtime lookup when it is not an exact integer, then takes the same tests on its i64 value, which a 32-bit target compares before truncating it.
73 lines
2.2 KiB
TypeScript
73 lines
2.2 KiB
TypeScript
// Element reads that may be undefined (`a[i]` as `T | undefined`, and the
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// stores `a[x] = a[y]!` read through) on arrays whose hole-free prefix
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// changes: holes from writes past the end and from a longer length, present
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// undefined, shrinking and regrowing, shift and unshift, out-of-range and
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// negative indices, and reads at a loop counter and at a computed index.
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function show(a: (number | undefined)[]): string {
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const out: string[] = [];
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for (let i = -1; i <= a.length; i++) {
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const v = a[i];
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out.push(v === undefined ? (i in a ? "u" : "_") : String(v));
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}
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return out.join(",");
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}
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const a: (number | undefined)[] = [10, 11, 12, 13, 14, 15];
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console.log(show(a));
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a[8] = 18;
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console.log(show(a), 7 in a);
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a.length = 9;
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console.log(show(a));
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a[7] = 17;
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console.log(show(a));
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a.length = 3;
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console.log(show(a));
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a.push(30, 31);
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console.log(show(a));
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a.unshift(1);
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console.log(show(a));
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a.shift();
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a.shift();
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console.log(show(a));
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const withUndefined: (number | undefined)[] = [1, undefined, 3];
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console.log(show(withUndefined));
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// Copies through the read: a hole stores undefined, which `in` then sees.
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function rotate(p: number[], r: number): void {
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const first = p[0]!;
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for (let i = 0; i < r; i++) p[i] = p[i + 1]!;
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p[r] = first;
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}
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const p: number[] = [0, 1, 2, 3, 4];
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rotate(p, 4);
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console.log(p.join(","));
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const holes: number[] = new Array<number>(4);
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holes[0] = 0;
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holes[1] = 1;
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holes[3] = 3;
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rotate(holes, 3);
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console.log(holes.length, 1 in holes, holes[1] === undefined, holes.join(","));
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// Reads at a computed index and at an index beyond the capacity.
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function pick(src: number[], idx: number[]): string {
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const out: string[] = [];
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for (const k of idx) {
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const v = src[k * 2];
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out.push(v === undefined ? "-" : String(v));
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}
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return out.join(",");
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}
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const big: number[] = [];
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for (let k = 0; k < 40; k++) big.push(k * k);
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console.log(pick(big, [0, 1, 5, 19, 20, 1000, -1, 2 ** 31]));
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big.length = 10;
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console.log(pick(big, [0, 4, 5, 6]));
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// Swaps at two counters, then reads of the swapped array.
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const q: number[] = [5, 4, 3, 2, 1, 0];
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for (let lo = 0, hi = q.length - 1; lo < hi; lo++, hi--) {
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const t = q[lo]!;
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q[lo] = q[hi]!;
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q[hi] = t;
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}
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console.log(q.join(","), show(q));
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