Function trigSign

src/compute-engine/boxed-expression/trigonometry.ts:657–674

(operator: string, x: Expression)

  // specialValues of inv_operator function
  //
  type ConstructibleTrigValuesInverse = [
    [match_arg: Expression, match_arg_N: number],
    angle: [numerator: number, denominator: number],
  ][];
  const specialInverseValues = ce._cache<ConstructibleTrigValuesInverse>(
    'constructible-inverse-trigonometric-values-' + operator,
    () => {
      const cache: ConstructibleTrigValuesInverse = [];
      for (const [[n, d], value] of specialValues) {
        const r = value[inv_operator!];
        if (r === undefined) continue;
        const rn = r.N().re;
        if (Number.isNaN(rn)) continue;
        cache.push([
          [r, rn],
          [n, d],
        ]);
      }
      return cache;
    },