added 6 byte grid coding in 26 bit

added encode and decode maidenhead grid square QTH locator as capital letter into 4 byte (only 26 bit used)

tnc/helpers.py

@@ -253,3 +253,64 @@ def check_callsign(callsign:bytes, crc_to_check:bytes):
             return [True, bytes(call_with_ssid)]
     
     return [False, ""]
+
+
+
+def encode_grid(grid):
+    """
+    Args:
+      grid:string: maidenhead QTH locater [a-r][a-r][0-9][0-9][a-x][a-x]
+    Returns:
+      4 bytes contains 26 bit valid data with encoded grid locator
+    """
+    out_code_word = int(0)
+
+    grid = grid.upper() # upper case to be save
+
+    int_first = ord(grid[0])-65 # -65 offset for 'A' become zero, utf8 table
+    int_sec   = ord(grid[1])-65 # -65 offset for 'A' become zero, utf8 table
+
+    int_val = (int_first * 18) + int_sec # encode for modulo devisioni, 2 numbers in 1
+
+    out_code_word = (int_val & 0b111111111) # only 9 bit LSB A - R * A - R is needed
+    out_code_word = out_code_word << 9 # shift 9 bit left having space next bits, letter A-R * A-R
+
+    int_val = int(grid[2:4]) # number string to number int, highest value 99
+    out_code_word = out_code_word | (int_val & 0b1111111) # using bit OR to add new value
+    out_code_word = out_code_word << 7 # shift 7 bit left having space next bits, letter A-X
+
+    int_val = ord(grid[4])-65 # -65 offset for 'A' become zero, utf8 table
+    out_code_word = out_code_word | (int_val & 0b11111) # using bit OR to add new value
+    out_code_word = out_code_word << 5 # shift 5 bit left having space next bits, letter A-X
+
+    int_val = ord(grid[5])-65 # -65 offset for 'A' become zero, utf8 table
+    out_code_word = out_code_word | (int_val & 0b11111) # using bit OR to add new value
+
+    return out_code_word.to_bytes(length=4, byteorder='big')
+
+def decode_grid(b_code_word:bytes):
+    """
+    Args:
+      b_code_word:bytes: 4 bytes with 26 bit valid data LSB
+    Returns:
+      grid:str: upper case maidenhead QTH locater [A-R][A-R][0-9][0-9][A-X][A-X]
+    """
+    code_word = int.from_bytes(b_code_word, byteorder='big', signed=False)
+
+    grid = chr((code_word & 0b11111) + 65) 
+    code_word = code_word >> 5
+
+    grid = chr((code_word & 0b11111) + 65) + grid
+    code_word = code_word >> 7
+
+    grid = str(int(code_word & 0b1111111)) + grid
+    if (code_word & 0b1111111) < 10:
+        grid = '0' + grid
+    code_word = code_word >> 9
+
+    int_val = int(code_word & 0b111111111)
+    int_first = int_val // 18
+    int_sec   = int_val % 18
+    grid = chr(int(int_first)+65) + chr(int(int_sec)+65) + grid
+
+    return grid