From 1d83bab27d7050f9e20eb23d9ce7f14d4b366505 Mon Sep 17 00:00:00 2001
From: arobsn <87387688+arobsn@users.noreply.github.com>
Date: Wed, 13 Sep 2023 18:14:13 -0300
Subject: [PATCH] add char code based hexToBytes function

---
 src/abstract/utils.ts | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/abstract/utils.ts b/src/abstract/utils.ts
index ff5b0c4..2682f2f 100644
--- a/src/abstract/utils.ts
+++ b/src/abstract/utils.ts
@@ -44,6 +44,27 @@ export function hexToNumber(hex: string): bigint {
   return BigInt(hex === '' ? '0' : `0x${hex}`);
 }
 
+const enum HexCharCode {
+  ZERO = 48, // 0
+  NINE = 57, // 9
+  A_UP = 65, // A
+  F_UP = 70, // F
+  A_LO = 97, // a
+  F_LO = 102, // f
+}
+
+function charCodeToBase16(char: number) {
+  if (char >= HexCharCode.ZERO && char <= HexCharCode.NINE) {
+    return char - HexCharCode.ZERO;
+  } else if (char >= HexCharCode.A_UP && char <= HexCharCode.F_UP) {
+    return char - (HexCharCode.A_UP - 10);
+  } else if (char >= HexCharCode.A_LO && char <= HexCharCode.F_LO) {
+    return char - (HexCharCode.A_LO - 10);
+  }
+
+  throw new Error('Invalid byte sequence.');
+}
+
 /**
  * @example hexToBytes('cafe0123') // Uint8Array.from([0xca, 0xfe, 0x01, 0x23])
  */
@@ -52,12 +73,10 @@ export function hexToBytes(hex: string): Uint8Array {
   const len = hex.length;
   if (len % 2) throw new Error('padded hex string expected, got unpadded hex of length ' + len);
   const array = new Uint8Array(len / 2);
-  for (let i = 0; i < array.length; i++) {
-    const j = i * 2;
-    const hexByte = hex.slice(j, j + 2);
-    const byte = Number.parseInt(hexByte, 16);
-    if (Number.isNaN(byte) || byte < 0) throw new Error('Invalid byte sequence');
-    array[i] = byte;
+  for (let i = 0, j = 0, l = array.length; i < l; i++) {
+    const n1 = charCodeToBase16(hex.charCodeAt(j++));
+    const n2 = charCodeToBase16(hex.charCodeAt(j++));
+    array[i] = n1 * 16 + n2;
   }
   return array;
 }