ebcdic-overpunch-decoding

name	ebcdic-overpunch-decoding
description	Reference for the EBCDIC "overpunch" / zoned-decimal sign convention where the units position of a numeric field is replaced with a letter that encodes both a digit and a sign. Useful when reading mainframe-style fixed-length tapes whose amount fields appear as digits followed by a letter (e.g. "0000000000123D" or "0000000000045M").

EBCDIC overpunch (zoned decimal sign)

On classic mainframe tapes, signed numeric amounts are stored as N-1 digits followed by a single byte where the high-order bits carry the sign and the low-order bits carry the final decimal digit. When the file is converted to ASCII / printable form, the last byte is rendered as a letter (or a brace).

Sign and digit table

Char	Sign	Last digit		Char	Sign	Last digit
{	+	0		}	−	0
A	+	1		J	−	1
B	+	2		K	−	2
C	+	3		L	−	3
D	+	4		M	−	4
E	+	5