ALT by Bilal Ahmed Shaik - HTML preview

  Assembly Constants

  There are several directives provided by NASM that define constants. We have already used the EQU directive in previous chapters. We will particularly discuss three directives:

   EQU

   %assign

   %define

  The EQU Directive

  The EQU directive is used for defining constants. The syntax of the EQU directive is as follows:

  For example,

  You can then use this constant value in your code, like:

  The operand of an EQU statement can be an expression:

  Above code segment would define AREA as 200.

  Example:

  The following example illustrates the use of the EQU directive:

  When the above code is compiled and executed, it produces fol owing result:

  The %assign Directive

  The %assign directive can be used to define numeric constants like the EQU directive. This directive allows redefinition. For example, you may define the constant TOTAL as:

  Later in the code you can redefine it as:

  This directive is case-sensitive.

  The %define Directive

  The %define directive allows defining both numeric and string constants. This directive is similar to the #define in C. For example, you may define the constant PTR as:

The above code replaces PTR by [EBP+4].

  This directive also allows redefinition and it is case sensitive.