Mumbai University > Computer Engineering > Sem6 > System Programming and Compiler Construction

Marks: 10M

Year: Dec 2015

MACRO

• In an assembly language program there can be group of instructions that may be repeated again and again.
• So we combine these instruction to a single group and assign a name to it which is called as MACRO.
• A macro is an extension to the basic ASSEMBLER language. They provide a means for generating a commonly used sequence of assembler instructions/statements.
• The sequence of instructions/statements will be coded ONE time within the macro definition. Whenever the sequence is needed within a program, the macro will be "called"

• MACRO is defined as a single line abbreviation for a group of instruction.

  Syntax :

  Macro
  Macro name

  } macro body

MEND

• Execution is faster in macro .There is no transfer of control in Macro.

• Features of Macro processor:

  1) Recognized the macro definition.

  2) Save macro definition.

  3) Recognized the macro call.

  4) Perform macro expansion.

Conditional Macro

• The macro processor replaces each macro instruction with the corresponding group of source language statements. This is called macro expansion or expanding the macros

• Conditional assembly are frequently considered to be mechanisms that allow a single version of the source code for a program to be used to generate multiple versions of the executable.

• Most macro processors can also modify the sequence of statements generated for a macro expansion, depending on the arguments supplied in the macro invocation. Conditional Assembly is commonly used to describe this feature. It is also referred to as conditional macro expansion.

• Conditional Assembly can be achieved with the help of AIF and AGO statements.

1) AIF Statement

• It is used to specify the branching condition.
• This statements provides conditional branching facility.

• Syntax :

  AIF (condition) Label

• If condition is satisfied the label is executed else it continue with the next execution.

• It performs an arithmetic test and branches only if tested condition is true.

2) AGO Statement

• This statement provides the unconditional branching facilities.
• We do not specify the condition
• Syntax:

AGO. Label

• It specifies the label appearing on some other statement in the macro instruction definition.
• The macro processor continues the sequential processing of instructions with the indicated statement.
• These statements are directives to the macro processor and do not appear in macro expansion.

Labels staring with a period (.), such as .FINI, are macro labels and do not appear in the output of the macro processor.

• FINI directs the macro processor to skip to the statement labelled.

3) LCL Statement:

• This statement is used for defining the Local Variables (Expansion variables).
• Local variables are always initialize to zero.

4) SET Statement:

• This statement is used for manipulating the value of expansion variables.
• It is used to make the updation in Local variables.

5) ANOP Statement:

• This statement performs no operations.