The following information refers to the so-called
“overlay information” especially being very significant for the programs
CODING2 and CODING3.
“Overlay” means the possibility to modify a key
manually or by a second dataset in a specific way resulting in a so-called
derived key. Changes can be restricted to definite positions in the key, to
particular key values, and to certain changing values inside the overlay
information. (overlay information limitation).
With that it is possible to overwrite values at
“chance” positions in the present key by “chance” values derived by the overlay
information.
Overlay information are only used if the corresponding
checkbox field “with overlay information” below
the initial key input field is switched on or a parameter
dataset is used in the state of “overlay once again”.
In general every single overlay information is
constructed by two values:
·
the position value and
·
the value which the overlay value is derived from.
Carrying out overlay processing, an input value or a
dataset value first is transformed by
CODING1:
overlay
value := (input-/dataset-value + present key value * 113
+
key value at previous position or at position 256 for position 1) modulo 256
CODING2:
overlay
value := (input-/dataset-value + present key value * 30,781
+
key value at previous position or at position 65,536 for position
1) modulo 65,536
CODING3:
overlay
value := (input-/dataset-value + present key value *
100,000,000,019
+key value at previous position or
at position 16,777,216 for
position 1) modulo 16,777,216
before the result-value is used as actual overlay
value.
Doing this in general, it is possible that a position
in the key can be overlaid repeatedly. After overlaying a position in fact, the
overlay value is the new key value for the further overlay processing. The last
overlay information applied to a position decides the value being the final key
value at this position.
You can
enter overlay information in metasyntax or in direct
mode using the overlay information input field (in
direct form) or in form of overlay datasets
in which overlay datasets in direct mode have a
special position using key overlaying.
If a parameter dataset is
used and only a parameter dataset handling takes place, you have the
possibility to overlay the key of the parameter dataset once again in further
program tasks by
activating the checkbox field “save after overlay”. To do so, the
parameter dataset is stored in state “overlay once again” and program
terminates if the current overlay operation is done.