add random non coding base instead of just A

file_to_dna.py

@@ -114,7 +114,7 @@ def encode_file(input_path: str, output_path: str) -> None:
 
     binary_string = convert_file_to_bits(input_path) # get the binary string representing the file content
 
-    dna_payload_size = bdc.size_of_dna_from_bit_len_abaab(len(binary_string) + CHECK_SUM_SIZE) # length of the payload after conversion in dna
+    dna_payload_size = bdc.size_dna_from_bit_len_abaab(len(binary_string) + CHECK_SUM_SIZE) # length of the payload after conversion in dna
     #print("payload size",str(dna_payload_size))
     
     # estimate number of blocks, round up to next int
@@ -138,8 +138,8 @@ def encode_file(input_path: str, output_path: str) -> None:
         exit(1)
         pass
     
-    # add a non coding A at the end of the sequence to make the last block at correct size when it is not possible to do by adding bits of 0 (very rare case)
-    add_A_at_end = False
+    # add a non coding base at the end of the sequence to make the last block at correct size when it is not possible to do by adding bits of 0 (very rare case)
+    add_base_at_end = False
     
     
     if force_size_to_max or total_dna_size % block_number > 0: # need to add non payload bits to adjust the size of blocks
@@ -158,16 +158,16 @@ def encode_file(input_path: str, output_path: str) -> None:
         filler_length = bdc.size_binary_from_dna_len_abaab(dna_payload_needed_size) - len(binary_string) - CHECK_SUM_SIZE
         #print("dna_payload_needed_size",str(dna_payload_needed_size)," +",filler_length,"bits")
     
-        # fill with '0' at the beginning of the binary # not the end because some zip can end with octets of 0, wich makes difficult to remove only the non coding '0'
+        # fill with '0' at the beginning of the binary # not the end because some zip can end with octets of 0, which makes difficult to remove only the non coding '0'
         binary_string = math.ceil(filler_length) * "0" + binary_string
         
         #print("updated binary size", str(len(binary_string)))
         
         # rare case where adding 0 can not solve the problem of round blocks
         if dna_payload_needed_size % 5 == 3:
-            # need a non coding A at the end
-            #print("added A")
-            add_A_at_end = True
+            # need a non coding base at the end
+            #print("added non coding base")
+            add_base_at_end = True
 
     
     # apply a filter to the binary string -> shuffle the data to avoid long rows of 0 or 1, and avoid rows repetitions 
@@ -182,7 +182,7 @@ def encode_file(input_path: str, output_path: str) -> None:
     # convert binaries into dna sequence
     sequence = bdc.binary_to_dna_abaab(filtered_binary_string)
     
-    if add_A_at_end: sequence += "A"
+    if add_base_at_end: sequence += bdc.bit_to_dna_balance_GC("0", sequence[-1]) # add a non coding base different from the preceding one
     
     total_sequence_size = len(sequence)+ dna_non_payload_size