mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-11-08 08:44:37 +08:00
Chris Tate
de6ef6590f
An element read that may be undefined, lowered inline from `%arr.idxOr` (`a[i]` as `T | undefined`, and the read in `a[x] = a[y]!`), took an integer index only from a loop's integer slot. Any other index, such as a double counter with a proven integer range or `k | 0`, was converted and tested for an exact integer on every read. The read now takes the same exact integer as a borrowed read does (`exactInteger`), on 64-bit targets. The loop-induction treatment above the hole-free prefix still applies only to a loop's integer slot.
71 lines
2.3 KiB
TypeScript
71 lines
2.3 KiB
TypeScript
// Element reads that may be undefined, at indices with a proven integer
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// range: loop counters with an unknown limit, `i | 0`, `x >>> 0`, negative
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// counters, -0, indices past the length and the capacity, and copies
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// `a[x] = b[y]!` that meet holes.
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function copy(src: number[], n: number): number[] {
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const out: number[] = new Array<number>(n);
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for (let i = 0; i < n; i++) out[i] = src[i]!;
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return out;
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}
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const src: number[] = [1, 2, 3, 4];
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const copied = copy(src, 6);
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console.log(copied.length, copied.join(","), 4 in copied, copied[5] === undefined);
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const holes: number[] = new Array<number>(5);
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holes[0] = 10;
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holes[3] = 13;
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const fromHoles = copy(holes, 5);
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console.log(fromHoles.join(","), 1 in fromHoles, 3 in fromHoles);
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function show(a: (string | undefined)[], from: number, to: number): string {
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const out: string[] = [];
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for (let i = from; i < to; i++) {
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const v = a[i];
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out.push(v === undefined ? "_" : v);
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}
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return out.join(",");
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}
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const words: (string | undefined)[] = ["a", undefined, "c"];
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words[5] = "f";
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console.log(show(words, -3, 8));
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console.log(show(words, 0, 0), show(words, 2, 1));
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function masked(a: number[], keys: number[]): string {
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const out: string[] = [];
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for (const k of keys) {
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const v = a[k | 0];
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const w = a[k >>> 0];
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out.push(`${v === undefined ? "-" : v}/${w === undefined ? "-" : w}`);
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}
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return out.join(" ");
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}
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const values: number[] = [5, 6, 7];
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console.log(masked(values, [0, 1.9, 2, 3, -1, -0, 4294967297, 2 ** 31]));
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const negativeZero = -0;
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console.log(values[negativeZero], values[0 * -1], Object.is(negativeZero, -0));
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// A counter that starts below zero and one that passes the capacity.
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let total = 0;
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for (let i = -2; i < values.length + 3; i++) total += values[i] ?? 100;
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console.log(total);
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const big: number[] = [];
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for (let k = 0; k < 20; k++) big.push(k);
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big.length = 10;
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let seen = 0;
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for (let i = 0; i < 40; i++) if (big[i] !== undefined) seen++;
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console.log(seen, big.length);
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// Rotations through the read, with a hole that becomes undefined.
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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 ring: number[] = new Array<number>(4);
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ring[0] = 0;
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ring[1] = 1;
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ring[3] = 3;
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rotate(ring, 3);
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console.log(ring.join(","), 1 in ring, ring[1] === undefined);
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