Microsoft KB Archive/74508

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The Lower Order Word of 32-Bit ROP Codes

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Q74508

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The information in this article applies to:


 * Microsoft Windows Device Development Kit (DDK) for Windows, versions 3.0, 3.1, 3.11

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SUMMARY
In Chapter 14 of the &quot;Microsoft Windows Device Development Kit Device Driver Adaptation Guide,&quot; 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:

  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 &quot;+&quot; represents a &quot;push&quot;, and the &quot;-&quot; represents a &quot;pop&quot;. Sixteen of the 256 ROPs cannot be represented without using &quot;push&quot; and &quot;pop&quot;.   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   Five logic operations. The logic operations could be any of the following: NOT

XOR

OR

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

Example 1:

85, 0085 1E05, PDSPnoaxn, D = not ((((not P) or S) and D) xor P) 1E08 = 00 01 11 10 00 0 001 01 | |  |  |  |  |  |  |       |  |  |  |  |  |  |  |___ 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:

<pre class="CODESAMP">SPDSPDSP After the bias, it will be:

<pre class="CODESAMP">PDSPDSPS The number of binary logic operations + 1 gives an index into the new string of the first operand. In this case, there are three binary operations, so the first operand will be the fourth element of the string (P), the second operand will be the third element (S), and so forth.

Example 2:

<pre class="CODESAMP">71, 0071 1D5C, SSDxPDxaxn, D = not (((D xor P) and (D xor S)) xor S) <pre class="FIXEDTEXT">1E08 = 00 01 11 01 01 0 111 00 | |  |  |  |  |  |  |       |  |  |  |  |  |  |  |___ 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:

<pre class="CODESAMP">S+SD-PDS

The number of binary logic operations + 1 normally gives an index into the string of the first operand. When a push/pop is involved, this must be biased by 2 to account for the encoded push/pop. In this case, there are four binary operations, plus a push and a pop, so the first operand will be the seventh element of the string (D), the second operand will be the sixth element (P), and so forth.

Additional query words: 3.00

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