Class QuantizedPointMap

js/meshIndex.js:26–104

 * Grid policy note: callers pass their own `quant`. The app currently uses
 *   1e4 (0.1 µm... 100 µm cells) — export grid, masking, validation, repair
 *   1e5 (10 µm cells)            — subdivision, regularize, displacement
 *   1e6 (1 µm cells)             — decimation (own packed-BigInt welder)
 * Keep a call site's grid unchanged unless you intend to change behaviour.
 */

export class QuantizedPointMap {
  /**
   * @param {number} quant     – grid multiplier (e.g. 1e5 → 10 µm cells)
   * @param {number} expected  – expected number of unique points (sizing hint)
   */
  constructor(quant, expected = 256) {
    this.quant = quant;
    /** true when the last getOrSet() inserted a new key */
    this.inserted = false;
    this._size = 0;
    let cap = 16;
    const target = Math.max(16, Math.ceil(expected / 0.6));
    while (cap < target) cap *= 2;
    this._alloc(cap);
  }

  get size() { return this._size; }

  _alloc(cap) {
    this._cap = cap;
    this._mask = cap - 1;
    this._qx = new Float64Array(cap);
    this._qy = new Float64Array(cap);
    this._qz = new Float64Array(cap);
    this._val = new Int32Array(cap).fill(-1);
  }

  _slot(qx, qy, qz) {
    // Mix the (wrapped-to-32-bit) quantised components; equality is checked
    // against the exact f64-stored values, so hash wrapping is harmless.
    let h = Math.imul(qx | 0, 0x9E3779B1) ^ Math.imul(qy | 0, 0x85EBCA77) ^ Math.imul(qz | 0, 0xC2B2AE3D);
    h ^= h >>> 15;
    let i = h & this._mask;
    const qxA = this._qx, qyA = this._qy, qzA = this._qz, val = this._val, mask = this._mask;
    while (val[i] !== -1) {
      if (qxA[i] === qx && qyA[i] === qy && qzA[i] === qz) return i;
      i = (i + 1) & mask;
    }
    return i;
  }

  _grow() {
    const oqx = this._qx, oqy = this._qy, oqz = this._qz, oval = this._val, ocap = this._cap;
    this._alloc(ocap * 2);
    for (let i = 0; i < ocap; i++) {
      if (oval[i] === -1) continue;
      const s = this._slot(oqx[i], oqy[i], oqz[i]);
      this._qx[s] = oqx[i]; this._qy[s] = oqy[i]; this._qz[s] = oqz[i];
      this._val[s] = oval[i];
    }
  }

  /** Value stored for (x,y,z)'s grid cell, or -1 if absent. */