The Lower Order Word of 32-Bit ROP Codes

• Microsoft Windows Device Driver Kit (DDK) for Windows versions 3.0, 3.1 and 3.11

SUMMARY

In Chapter 14 of the "Microsoft Windows Device Development Kit Device Driver Adaptation Guide," the interpretation of the raster operation (ROP) code is explained. However, only the higher-order word or most-significant word (MSW) of the 32-bit ROP code is explained. This word is an index in the ROP table. The use of the lower-order word or least-significant word (LSW) of the ROP code is not addressed in the Windows Device Development Kit (DDK).

The LSW of the ROP code may be used by display drivers to assist in parsing the ROP. A complete explanation of the LSW of the ROP code can be found in the file COMMENT.BLT, which is included with the DDK display driver sample source code. This file is found in the directory that contains the source code for the BitBlt routine. For example, the file that relates to the VGA/EGA driver is found in the DISPLAY\4PLANE\BITBLT directory.

Note: The LSW of the ROP code is NOT used by the VGA/EGA, 8514, and other display drivers distributed by Microsoft. Windows Graphics Device Interface (GDI) does not process the LSW. GDI simply passes it to the display driver.

The relevant section from the COMMENT.BLT file is included below.

MORE INFORMATION

The low-order word in and of itself does not contain enough information to generate the ROP code. What it contains is:

1. An index specifying which predefined parse sting to use. A parse string has a format similar to

         SDPSDPSD
   

   or

         S+SD-PDS
   

   where S, D, and P represent source, destination, and pattern. The "+" represents a "push", and the "-" represents a "pop". Sixteen of the 256 ROPs cannot be represented without using "push" and "pop".

2. Amount to rotate the parse string. If the base string is

         SDPSDPSD
   

   and an offset of 2 was given, the new base string will be:

         PSDPSDSD
   

3. Five logic operations. The logic operations could be any of the following:

         NOT
         XOR
         OR
         AND
   

4. A parity bit used to imply a sixth logic operation of NOT. Pairs of trailing NOTs are discarded since they cancel.

           D = not ((((not P) or S) and D) xor P)

       |  |  |  |  |  |  |  |
       |  |  |  |  |  |  |  |___ bias start by 1
       |  |  |  |  |  |  |______ use string 1
       |  |  |  |  |  |_________ parity - no trailing NOT
       |  |  |  |  |____________ Logic operation #1 is a NOT
       |  |  |  |_______________ Logic operation #2 is a OR
       |  |  |__________________ Logic operation #3 is a AND
       |  |_____________________ Logic operation #4 is a XOR
       |________________________ Logic operation #5 is a NOT


String #1 is defined as:      SPDSPDSP

After the bias, it will be:   PDSPDSPS

Example 2: 71, 0071 1D5C, SSDxPDxaxn,

           D = not (((D xor P) and (D xor S)) xor S)

       |  |  |  |  |  |  |  |
       |  |  |  |  |  |  |  |___ don't bias start
       |  |  |  |  |  |  |______ use string 7
       |  |  |  |  |  |_________ parity - no trailing NOT
       |  |  |  |  |____________ Logic operation #1 is a XOR
       |  |  |  |_______________ Logic operation #2 is a XOR
       |  |  |__________________ Logic operation #3 is a AND
       |  |_____________________ Logic operation #4 is a XOR
       |________________________ Logic operation #5 is a NOT


String #7 is defined as:      S+SD-PDS