Here’s a bit of innocuous code. It was being compiled with gcc -fexec-charset=1047, so all the characters and strings were being treated as EBCDIC. For example ‘0’ = ‘\xF0’.

    if (c >= '0' && c <= '9')                                                                                                         
         c -= '0';                                                                                                                    
    else if (c >= 'A' && c <= 'Z')                                                                                                    
         c -= 'A' - 10;                                                                                                               
    else if (c >= 'a' && c <= 'z')                                                                                                    
         c -= 'a' - 10;                                                                                                               

Specifying the charset is not enough to port this code to the mainframe.  The problem is that EDCDIC is completely braindead, and DOESN’T PUT THE FRIGGEN LETTERS TOGETHER!

The letters are clustered in groups:

  • a-i
  • j-r
  • s-z
  • A-I
  • J-R
  • S-Z

with whole piles of crap between each range of characters, so comparisons like c >= ‘A’ && c <= ‘Z’ are useless, as are constructions like (c-‘A’-10) since c in J-R or S-Z will break that.

Now I have a big hunt and destroy task ahead of me.  I can fix this code, but where else are problems like this lurking!