Compare hashing implementations

Author: rolodato

flagsmith-engine/utils/hashing/index.ts

@@ -5,6 +5,51 @@ const md5 = (data: BinaryLike) => createHash('md5').update(data).digest('hex')
 const makeRepeated = (arr: Array<any>, repeats: number) =>
     Array.from({ length: repeats }, () => arr).flat();
 
+function h2d(s: any): string {
+    function add(x: any, y: any) {
+        var c = 0,
+            r = [];
+        var x = x.split('').map(Number);
+        var y = y.split('').map(Number);
+        while (x.length || y.length) {
+            var s = (x.pop() || 0) + (y.pop() || 0) + c;
+            r.unshift(s < 10 ? s : s - 10);
+            c = s < 10 ? 0 : 1;
+        }
+        if (c) r.unshift(c);
+        return r.join('');
+    }
+
+    var dec = '0';
+    s.split('').forEach(function (chr: any) {
+        var n = parseInt(chr, 16);
+        for (var t = 8; t; t >>= 1) {
+            dec = add(dec, dec);
+            if (n & t) dec = add(dec, '1');
+        }
+    });
+    return dec;
+}
+
+
+import bigInt from 'big-integer'
+export function getHashedPercentateForObjIdsOld(objectIds: Array<any>, iterations = 1): number {
+    let toHash = makeRepeated(objectIds, iterations).join(',');
+    const hashedValue = md5(toHash);
+    const hashedInt = bigInt(h2d(hashedValue));
+    const value = (hashedInt.mod(9999).toJSNumber() / 9998) * 100;
+
+    // we ignore this for it's nearly impossible use case to catch
+    /* istanbul ignore next */
+    if (value === 100) {
+        /* istanbul ignore next */
+        return getHashedPercentateForObjIdsOld(objectIds, iterations + 1);
+    }
+
+    return value;
+}
+
+
 // https://stackoverflow.com/questions/12532871/how-to-convert-a-very-large-hex-number-to-decimal-in-javascript
 /**
  * Given a list of object ids, get a floating point number between 0 and 1 based on

package-lock.json

@@ -69,6 +69,7 @@
     "@types/semver": "^7.3.9",
     "@types/uuid": "^8.3.4",
     "@vitest/coverage-v8": "^2.1.2",
+    "big-integer": "^1.6.52",
     "esbuild": "^0.14.25",
     "husky": "^7.0.4",
     "prettier": "^2.2.1",

package.json

@@ -1,7 +1,21 @@
 import { randomUUID as uuidv4 } from 'node:crypto';
-import { getHashedPercentateForObjIds } from '../../../../flagsmith-engine/utils/hashing/index.js';
+import {
+    getHashedPercentateForObjIds,
+    getHashedPercentateForObjIdsOld
+} from '../../../../flagsmith-engine/utils/hashing/index.js';
 
 describe('getHashedPercentageForObjIds', () => {
+    test('is equivalent to the previous implementation', () => {
+        for (let i = 0; i < 10000; i++) {
+            const data = [uuidv4()]
+            const a = getHashedPercentateForObjIdsOld(data)
+            const b = getHashedPercentateForObjIds(data)
+            console.log(a, b)
+            expect(a).toEqual(b)
+        }
+    })
+    
+    
     it.each([
         [[12, 93]],
         [[uuidv4(), 99]],