optimize helper code

Software/src/helpers.cpp

@@ -1,69 +1,87 @@
 #include "helpers.h"
 
-void char2byte(char *str, byte *array)
+// Helper: convert a single hex char into a nibble (4 bits)
+static inline uint8_t hex2nibble(char c)
 {
-    for (int i = 0; i < 2; i++)
-    {
-        char c = *str;
     if (c >= '0' && c <= '9')
     {
-            *array *= 16;
-            *array += c - '0';
+        return c - '0';
     }
-        else if (c >= 'A' && c <= 'F')
+    if (c >= 'A' && c <= 'F')
     {
-            *array *= 16;
-            *array += (c - 'A') + 10;
+        return c - 'A' + 10;
     }
-        else if (c >= 'a' && c <= 'f')
+    if (c >= 'a' && c <= 'f')
     {
-            *array *= 16;
-            *array += (c - 'a') + 10;
-        }
-        str++;
+        return c - 'a' + 10;
     }
+    return 0; // or handle error
 }
 
-void chars2bytes(char *str, byte *array, bool msb)
+// Convert two hex characters to a byte.
+void char2byte(const char *str, uint8_t *value)
 {
-    int len = strlen(str);
-    for (int i = 0; i < len; i += 2)
-    {
+    *value = (hex2nibble(str[0]) << 4) | hex2nibble(str[1]);
+}
+
+// Convert a hex string (2 chars per byte) into a byte array.
+// If msb is true, the first two chars go into array[0]; if false, the byte order is reversed.
+void chars2bytes(const char *str, uint8_t *array, bool msb)
+{
+    size_t len = strlen(str);
+    size_t byteCount = len / 2;
+
     if (msb)
     {
-            char2byte(&str[i], &array[i / 2]);
+        for (size_t i = 0; i < byteCount; i++)
+        {
+            array[i] = (hex2nibble(str[2 * i]) << 4) | hex2nibble(str[2 * i + 1]);
+        }
     }
     else
     {
-            char2byte(&str[i], &array[len - 2 - i / 2]);
-        }
-    }
-}
-
-void byte2char(byte *array, char *str)
-{
-    sprintf(str, "%02x", *array);
-}
-
-void bytes2chars(byte *array, byte array_len, char *str, bool msb)
-{
-    for (int i = 0; i < array_len; i++)
+        for (size_t i = 0; i < byteCount; i++)
         {
+            array[byteCount - 1 - i] = (hex2nibble(str[2 * i]) << 4) | hex2nibble(str[2 * i + 1]);
+        }
+    }
+}
+
+// Convert a single byte into two hex characters.
+void byte2char(uint8_t value, char *str)
+{
+    const char hexDigits[] = "0123456789abcdef";
+    str[0] = hexDigits[value >> 4];
+    str[1] = hexDigits[value & 0x0F];
+    str[2] = '\0';
+}
+
+// Convert an array of bytes to a hex string.
+// If msb is true, the order is maintained; if false, the order is reversed.
+void bytes2chars(const uint8_t *array, size_t array_len, char *str, bool msb)
+{
     if (msb)
     {
-            byte2char(&array[i], &str[i * 2]);
+        for (size_t i = 0; i < array_len; i++)
+        {
+            byte2char(array[i], &str[i * 2]);
+        }
     }
     else
     {
-            byte2char(&array[array_len - 2 - i], &str[i * 2]);
+        for (size_t i = 0; i < array_len; i++)
+        {
+            byte2char(array[array_len - 1 - i], &str[i * 2]);
         }
     }
+    str[array_len * 2] = '\0';
 }
 
-void printbytes(byte *array, byte array_len)
+// Print a byte array in hexadecimal format.
+void printbytes(const uint8_t *array, size_t array_len)
 {
     Serial.print("0x");
-    for (int i = 0; i < array_len; i++)
+    for (size_t i = 0; i < array_len; i++)
     {
         Serial.printf("%02x", array[i]);
     }

Software/src/helpers.h

@@ -2,12 +2,36 @@
 #define HELPERS_H
 
 #include <Arduino.h>
-void char2byte(char *str, byte *array);
-void chars2bytes(char *str, byte *array, bool msb);
-
-void byte2char(byte *array, char *str);
-void bytes2chars(byte *array, byte array_len, char *str, bool msb);
-
-void printbytes(byte *array, byte array_len);
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
 
+#ifdef __cplusplus
+extern "C"
+{
 #endif
+
+    // Convert two hex characters to a byte.
+    void char2byte(const char *str, uint8_t *value);
+
+    // Convert a hex string (2 characters per byte) into a byte array.
+    // If msb is true, the first two characters go into array[0];
+    // if false, the resulting bytes are stored in reverse order.
+    void chars2bytes(const char *str, uint8_t *array, bool msb);
+
+    // Convert a single byte into two hex characters.
+    void byte2char(uint8_t value, char *str);
+
+    // Convert an array of bytes to a hex string.
+    // If msb is true, the order is maintained;
+    // if false, the byte order is reversed.
+    void bytes2chars(const uint8_t *array, size_t array_len, char *str, bool msb);
+
+    // Print a byte array in hexadecimal format.
+    void printbytes(const uint8_t *array, size_t array_len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // HELPERS_H