Slide 5.13: Calculating data sizes and EQU directive

Slide 5.12: Symbolic constants
Slide 5.14: TEXTEQU directive
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Calculating Data Sizes and EQU Directive

The ‘$’ operator (current location counter) returns the offset associated with the current program statement.

String Size	Array Size	Instruction Size
INCLUDE Irvine32.inc .data s BYTE "Hello, world!" len = .code main PROC mov eax, len call WriteInt exit main ENDP END main	INCLUDE Irvine32.inc .data a WORD 10, 20, 30, 40 len = .code main PROC mov eax, len call WriteInt exit main ENDP END main	INCLUDE Irvine32.inc .data Dummy WORD ? .code main PROC add eax, eax len = $ - a1 mov eax, len call WriteInt exit main ENDP END main
Output	Output	Output
13	4	2

The directive associates a symbolic name with an integer expression or some text.

name  EQU  expression
name  EQU  symbol
name  EQU  <text>

In the first format, must be a valid integer expression.
In the second format, is an existing symbol name, already defined with ‘=’ or .
In the third format, any text may appear within the brackets <...>.

When the assembler encounters later in the program, it substitutes the integer value or text for the symbol. Code 3 and 4 are equal. stores the integer value 200, and stores the string “20 * 10” .

Code 3	myInt EQU 20 * 10 myString EQU <20 * 10> .data myWord1 WORD myInt myWord2 WORD myString
Code 4	.data myWord1 WORD 200 myWord2 WORD 20 * 10

^†Unlike the ‘=’ directive, a symbol defined with cannot be redefined in the same source code.

“I’m not arguing, I’m just explaining why I’m right.”
― Unknown