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Defining your own directives

The commands .MACRO and .ENDM allow you to define macros that generate assembly output. You can use these macros with a syntax similar to built-in GASP or assembler directives. For example, the following input definition specifies a macro SUM that adds together a range of consecutive registers.

          .MACRO     SUM FROM=0,     TO=9
          ! \FROM \TO
          mov          r\FROM,r10
COUNT     .ASSIGNA     \FROM+1
          .AWHILE \&COUNT LE \TO
          add          r\&COUNT,r10
COUNT     .ASSIGNA          \&COUNT+1
          .AENDW
          .ENDM

With that definition, SUM 0,5 generates the following assembly output.

          !0 5
          mov          r0,r10
          add          r1,r10
          add          r2,r10
          add          r3,r10
          add          r4,r10
          add          r5,r10

.MACRO macname
.MACRO macname macargs...
Begin the definition of a macro called macname. If your macro definition requires arguments, specify their names after the macro name, separated by commas or spaces. You can supply a default value for any macro argument by following the name with = deflt. For example, the following are all valid .MACRO statements:

.MACRO COMM      
Begin the definition of a macro called
COMM, which takes no arguments.

.MACRO PLUS1 P, P1
.MACRO PLUS1 P P1     
Either statement begins the definition of a macro called PLUS1, which takes two arguments; within the macro definition, write \P or \P1 to evaluate the arguments.

.MACRO RESERVE_STR P1=0 P2
Begin the definition of a macro called RESERVE_STR, with two arguments. The first argument has a default value, but not the second. After the definition is complete, you can call the macro either as RESERVE_STR a, b (with \P1 evaluating to a and \P2 evaluating to b), or as RESERVE_STR , b (with \P1 evaluating as the default, in this case, 0, and \P2 evaluating to b).
When you call a macro, you can specify the argument values either by position, or by keyword. For example,
SUM 9,17 is equivalent to SUM TO=17, FROM=9. Macro arguments are preprocessor variables similar to the variables you define with .ASSIGNA or .ASSIGNC; in particular, you can use them in conditionals or for loop control. (The only difference is the prefix you write to evaluate the variable: for a macro argument, write \argname, but for a preprocessor variable, write \&varname.)

name .MACRO
name .MACRO ( macargs...)     
An alternative form of introducing a macro definition: specify the macro name in the label position, and the arguments (if any) between parentheses after the name. Defaulting rules and usage work the same way as for the other macro definition syntax.

.ENDM
Mark the end of a macro definition.

.EXITM
Exit early from the current macro definition,
.AREPEAT loop, or .AWHILE loop.

\@
GASP maintains a counter of how many macros it has executed in this pseudo-variable; you can copy that number to your output with
\@, but only within a macro definition.