format.txt

IPS Patch Format Specification
==============================

This file describes the format of IPS binary patches.

The file begins with a 5-byte header containing the ASCII string "PATCH"
without a NUL terminator.

Following the header are any number of patch records. Records come in two
variants: plain segments and RLE segments. Records are placed one after the
other with nothing in between. All numbers are big endian.

A plain record is structured as follows:

| Field  | Length | Description                                                       |
|--------+--------+-------------------------------------------------------------------|
| offset |      3 | Indicates the position in the file where the patch segment begins |
| size   |      2 | Indicates the number of data bytes to follow                      |
| data   |   size | The bytes to be written at offset                                 |

An RLE record describes a string of identical repeating bytes. It has the
structure:

| Field    | Length | Description                                               |
|----------+--------+-----------------------------------------------------------|
| offset   |      3 | Same as for plain records                                 |
| size     |      2 | Always set to 0 which signifies it as an RLE record       |
| rle_size |      2 | Indicates the number of times the data byte is repeated   |
| data     |      1 | The byte to be repeated rle_size times starting at offset |

At the end of all the records, the file ends with a 3-byte footer containing
the ASCII string "EOF" without a NUL terminator.