Refactor hex_to_bytes

utils.c

@@ -2,15 +2,17 @@
 #include <ctype.h>
 #include <string.h>
 
+unsigned char hex_to_byte(const char c) {
+  if (isdigit(c)) {
+    return c - '0';
+  }
+  return 10 + c - 'a';
+}
+
 size_t hex_to_bytes(unsigned char *out, const char hex[static 1]) {
   for (size_t i = 0; i < strlen(hex); ++i) {
     char c = tolower(hex[i]);
-    unsigned char value;
-    if (isdigit(c)) {
-      value = c - '0';
-    } else {
-      value = 10 + c - 'a';
-    }
+    unsigned char value = hex_to_byte(c);
     if (i % 2 == 0) {
       value <<= 4;
     }

utils.h

@@ -3,6 +3,7 @@
 
 #include <stdlib.h>
 
+unsigned char hex_to_byte(const char c);
 size_t hex_to_bytes(unsigned char *out, const char hex[static 1]);
 unsigned char *bytes_to_base64(unsigned char *out,
                                const unsigned char in[static 1], size_t len);