Line data    Source code

       1           1 : import { UINT32_MAX } from "./constants.ts";
       2             : 
       3             : /**
       4             :  * See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/imul
       5             :  */
       6           1 : export const imul: (a: number, b: number) => number = (() => {
       7           2 :   try {
       8           2 :     if ((Math as any).imul(UINT32_MAX, 5) === -5) {
       9           2 :       return (Math as any).imul;
      10           2 :     }
      11           2 :   } catch (_) {
      12             :     // nothing to do here
      13           0 :   }
      14           0 :   const UINT16_MAX = 0xffff;
      15           0 :   return (a: number, b: number) => {
      16           0 :     const ah = (a >>> 16) & UINT16_MAX;
      17           0 :     const al = a & UINT16_MAX;
      18           0 :     const bh = (b >>> 16) & UINT16_MAX;
      19           0 :     const bl = b & UINT16_MAX;
      20             :     // the shift by 0 fixes the sign on the high part
      21             :     // the final |0 converts the unsigned value into a signed value
      22           0 :     return (al * bl + (((ah * bl + al * bh) << 16) >>> 0)) | 0;
      23           0 :   };
      24           1 : })();