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refactor: extract alphabetToNumber helper, optimize SSN blacklist lookup #157

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refactor: extract alphabetToNumber helper, optimize SSN blacklist lookup #157

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7 changes: 3 additions & 4 deletions src/us/ssn.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ import * as exceptions from '../exceptions';
import { strings } from '../util';
import { Validator, ValidateReturn } from '../types';

const invalidSSN = [
const invalidSSNSet = new Set([

@koblas koblas Jun 15, 2026

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I will note that if this is a performance optimization, that object keys are the fastest with a if (value in invalidSSN) { as the check will out perform Set().

'111111111',
'222222222',
'333333333',
Expand All @@ -27,7 +27,6 @@ const invalidSSN = [
'888888888',
'999999999',
'123123123',
'999999999',

@gemini-code-assist gemini-code-assist Bot Jun 13, 2026

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medium

While removing the duplicate '999999999' is a good cleanup, the remaining '999999999' entry (now on line 28) is also completely redundant. Any SSN starting with 9 (including 999999999) is already rejected by the regex check /^(000|666|9)\d+/ on line 99. Therefore, both entries can be safely removed from the blacklist.

// Used in Advertising and known "invalid"
'002281852',
'042103580',
Expand All @@ -51,7 +50,7 @@ const invalidSSN = [
'457555462',
'468288779',
'549241889',
];
]);

function clean(input: string): ReturnType<typeof strings.cleanUnicode> {
return strings.cleanUnicode(input, '- ');
Expand Down Expand Up @@ -94,7 +93,7 @@ const impl: Validator = {
if (!strings.isdigits(value)) {
return { isValid: false, error: new exceptions.InvalidComponent() };
}
if (invalidSSN.includes(value)) {
if (invalidSSNSet.has(value)) {
return { isValid: false, error: new exceptions.InvalidComponent() };
}
if (/^(000|666|9)\d+/.test(value)) {
Expand Down
39 changes: 21 additions & 18 deletions src/util/checksum.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -80,7 +80,6 @@ export function luhnChecksumValidate(

const sum = value
.split('')
// .reverse()
.map(v => alphabet.indexOf(v))
.reduce((acc, val, idx) => {
let v = val;
Expand Down Expand Up @@ -213,32 +212,36 @@ function modulo(dividentIn: string, divisor: number) {
return parseInt(divident, 10) % divisor;
}

/**
* Convert a string using alphanumeric alphabet to its numeric representation.
* Returns null if any character is not in the alphabet.
*/
function alphabetToNumber(

@koblas koblas Jun 15, 2026

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this feels needless.

value: string,
alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
): string | null {
Comment on lines +219 to +222

@gemini-code-assist gemini-code-assist Bot Jun 13, 2026

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medium

Since the PR description mentions that this helper is intended to be reused by other functions/modules that need alphanumeric-to-numeric conversion, it should be exported so that other files can import it.

Suggested change
function alphabetToNumber(
value: string,
alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
): string | null {
export function alphabetToNumber(
value: string,
alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
): string | null {

let result = '';
for (const c of value) {
const idx = alphabet.indexOf(c);
if (idx === -1) {
return null;
}
result += String(idx);
}
return result;
}

/**
* The ISO 7064 Mod 97, 10 algorithm.
*
* The Mod 97, 10 algorithm evaluates the whole number as an integer which is
* valid if the number modulo 97 is 1. As such it has two check digits.
*/
export function mod97base10Validate(value: string, expect = 1): boolean {
const alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
let fail = false;

const bigValue = value
.split('')
.map(c => {
const idx = alphabet.indexOf(c);
if (idx === -1) {
fail = true;
return '';
}
return String(idx);
})
.join('');

if (fail) {
const bigValue = alphabetToNumber(value);
if (bigValue === null) {
return false;
}

return modulo(bigValue, 97) === expect;
}

Expand Down