Processing a long character string one character at a time

I have a routine that processes each character in a file. The file I am working with is over 2 million characters long. I pull it into a memory variable with filetostr and then process each character with the substr command. Apparently substr has problems when dealing with a long string as the process is painfully slow.

I suspect that I will be better off using the low level file routines to read one character at a time but thought maybe someone knows of a way to speed up the approach I am using now.

Thanks in advance,

Joe

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