C166/ST10 Cross-Assembler, Linker/Locator, Utilities ... - Tasking

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MACRO PREPROCESSOR
Chapter 2
2.7.8 ALGORITHM FOR EVALUATING MACRO CALLS
The algorithm of the macro preprocessor used for evaluating the source
file can be broken down into 6 steps:
1. Scan the input until the ’@’ character is found.
2. Isolate the macro−name.
3. If macro has parameters, expand each parameter from left to right (initiate
step one for actual parameter) before expanding the next parameter.
4. Substitute actual parameters for formal parameters in macro−body.
5. If the literal character is not used, initiate step one on macro−body.
6. Insert the result into output stream.
The terms ’input stream’ and ’output stream’ are used because the return
value of one macro may be a parameter to another. On the first iteration,
the input stream is the source line. On the final iteration, the output stream
is passed to the assembler.
Example:
The examples below illustrate the macro preprocessor’s evaluation
algorithm:
@SET( TOM, 3 )
@*DEFINE STEVE ()
@SET( TOM, @TOM −1 ) @TOM
@ENDD
@DEFINE ADAM( A, B )
DB @A, @B, @A, @B, @A, @B
@ENDD
The call ADAM is presented here in the normal mode with TOM as the
first actual parameter and STEVE as the second actual parameter. The first
parameter is completely expanded before the second parameter is
expanded. After the call to ADAM has been completely expanded, TOM
will have the value 02h.
Before Macro Expansion After Macro Expansion
@ADAM( @TOM, @STEVE ) −> DB 03h, 02h, 03h, 02h, 03h, 02h