Added hex.ts

Author: Stephen-Thomson

src/primitives/hex.ts

@@ -0,0 +1,23 @@
+// src/primitives/hex.ts
+
+const PURE_HEX_REGEX = /^[0-9a-fA-F]+$/
+
+export function assertValidHex (msg: string): void {
+  if (typeof msg !== 'string' || msg.length === 0 || !PURE_HEX_REGEX.test(msg)) {
+    throw new Error('Invalid hex string')
+  }
+}
+
+export function normalizeHex (msg: string): string {
+  assertValidHex(msg)
+
+  // Lowercase first
+  let normalized = msg.toLowerCase()
+
+  // Prepend "0" if odd-length
+  if (normalized.length % 2 === 1) {
+    normalized = '0' + normalized
+  }
+
+  return normalized
+}