International Patching System Format
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  This goal of this document is to detail the internals of the International
  Patching System (IPS) format.

  IPS is a simple patching system that is used to change certain bytes that
  have been changed.  Instead of redistributing large binaries around, one
  can distribute a much smaller IPS patch (depending on the number of
  changes).  It originated on the Amiga platform, where it was mainly used for distributing
  cracks to pirated console games.  However due to the generalization of the
  format it can be used patch anything.

  I would give the original author credit for creation of this format, but I
  don't know who he is!  If you can <A HREF="mailto:mindrape@goodnet.com,staheli@goodnet.com">email me</A> the correct information, I'll
  promptly update this document.

  In this version of this documentation the RLE compression scheme has been
  left out. I have never seen an IPS implementation use this before.


  An IPS patch can be of a variable size, but it can only address
  16777215 bytes.  This is because of the address bytes only being 3
  bytes.  And since there isn't strong support on other platforms
  that use the IPS format, i doubt people will switch to a 4 byte
  addressing scheme.

  An IPS file is made up of individual patches, which we will
  call clusters.  Each cluster can only be 64K max in size, due
  to the patch size being defined as 2 bytes.

  The only way to determine how many clusters there are is to
  go though the file, reading the Patch Size and skipping those
  bytes until you read the address, and patch size again. Then
  skip those byte, and keep going until you hit EOF marker and
  it is at the end of the file.

  IPS files have the extension of .IPS (i.e. smworld.ips).
  Here is the format to an IPS file.

  IPS Element
  Description

  Majic
  This is the signature of a IPS patch.  It is 5 bytes and should be the
  word "PATCH".

  Address
  The location in the binary to patch.  3 chars.

  Patch Size
  The number of bytes to patch for this cluster.  It is 2 bytes,
  therefore 64K maximum in size.

  Bytes to patch
  These are the modified bytes that need to be patched.  They are
  patched at the above address.<BR>Its size is variable, you can
  determine it's length by looking at the Patch Size.

  ...
  Address, Patch and Bytes to patch, repeated as many times as it wants.

  EOF
  This is the end of file marker. It is always located at the end of a
  IPS patch.  It could also be used to validate whether a IPS patch
  is complete.  3 chars = "EOF"


    Examples

 Here are some example patches to give you an idea of what is going on
 inside an IPS file.
 The following example contains 10 patches, each patch is exactly one byte.
 

    PATCHaaappbaaappbaaappbaaappbaaappbaaappbaaappbaaappbaaappbaaappbEOF


 The following example contains 3 patches, each patch is of the following
 byte sizes: 3, 10 and 5 bytes.


    PATCHaaappbbbaaappbbbbbbbbbbaaappbbbbbEOF





Keys
Description

PATCH
This is the signature of a IPS file.
It always resides at the start of every IPS file.

aaa
Address (3 Bytes)

pp
Patch Size (2 Bytes)

b
These are the changed bytes that need to replace the one
in the orginal binary.  There are pp number of these.


EOF
End of file marker.







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