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--- en:multiasm:papc:chapter_6_12 [2025/11/14 14:20] – [Conditional assembly directives] ktokarz
+++ en:multiasm:papc:chapter_6_12 [2026/02/27 02:10] (current) – [Statements] jtokarz
@@ Line 1: / Line 1: @@
-====== MASM basics ======
+====== MASM Basics ======
 An assembler, understood as software that translates assembler source code into machine code, can be implemented in various ways. While the processor's instructions remain constant, other language elements may be implementation-specific. In this chapter, we present the most important language elements specific to the MASM assembly implementation. For a detailed description of MASM assembler language implementation, please refer to the Microsoft© website((https://learn.microsoft.com/en-us/cpp/assembler/masm/microsoft-macro-assembler-reference?view=msvc-170)).
 ===== Alphabet =====
@@ Line 122: / Line 122: @@
-===== Important directives =====
+===== Selected directives =====
 The **ORG** directive sets the location counter to the specified value x. It is used to align the parts of the program to a specific address.
@@ Line 133: / Line 133: @@
 The **LABEL** directive creates a new label by assigning the current location-counter value and the given type to the defined name. Usually in a program, the **:** (colon) sign is used for label definition, but the **LABEL** directive enables specifying the type of element which the label points to.
+===== Data definition directives =====
 There is a set of directives for defining variables. They enable the assignment of a name to a variable and the specification of its type. They are summarised in a table
 {{ref>masmdatadefine}}.
@@ Line 190: / Line 191: @@
   loop clear
 </code>
+===== Constants =====
+Constants in an assembler program define the name for the value that can't be changed during normal program execution. It is the assembly-time assignment of the value and its name. Although their name suggests that their value can't be altered, it is true at the program run-time. Some forms of constants can be modified during assembly time. Usually, constants are used to self-document the code, parameterise the assembly process, and perform assembly-time calculations.
+The constants can be integer, floating-point numeric, or text strings.\\
+Integer numeric constants can be defined with the data assignment directives, **EQU** or the equal sign **=**. The difference is that a numeric constant defined with the EQU directive can’t be modified later in the program, while a constant created with the equal sign can be redefined many times in the program. Numeric constants can be expressed as binary, octal, decimal or hexadecimal values. They can also be a result of an expression calculated during assembly time. It is possible to use a previously defined constant in such an expression.
+<code asm>
+int_const1 EQU 5                ; no suffix by default decimal value
+int_const_dec = 7               ; finished with "d", "D", "t", "T", or
+                                ; by default without suffix
+int_const_binary = 100100101b   ; finished with "b", "B", "y", or "Y"
+int_const_octal = 372o          ; finished with "o", "O", "q", or "Q"
+int_const_hex = 0FFA4h          ; finished with "h", or "H"
+int_const_expr = int_const_dec * 5
+</code>
+Floating-point numeric constants can be defined with the **EQU** directive only. The number can be expressed in decimal or scientific notation.
+<code asm>
+real_const1 EQU 3.1415          ; decimal
+real_const2 EQU 6.28e2          ; scientific
+</code>
+Text string constants can be defined with **EQU** or **TEXTEQU** directives. Text constants assigned with the **EQU** or **TEXTEQU** directive can be redefined later in the program. The **TEXTEQU** is considered a text macro and is described in the section about macros.
+<code asm>
+text_const1 EQU 'Hello World!'
+text_const2 EQU "Hello World!"
+</code>
 ===== Conditional assembly directives =====
 The condition assembly directives have the same functionality as in high-level language compilers. They control the assembly process by checking the defined conditions and enabling or disabling the process for fragments of the source code.
-  * **IF** expression, **IFE** expression - test the value of the expression and perform (or do not) assemble according to the result (0-false).
+  * **IF** expression, **IFE** expression - tests the value of the expression and performs (or do not) assemble according to the result (0-false),
   * **IFDEF** symbol - tests whether a symbol is defined,
-  * **IFNDEF** symbol - tests whether a symbol is undefined.
+  * **IFNDEF** symbol - tests whether a symbol is undefined,
   * **IFB** <argument> - tests whether the string argument is empty,
   * **IFNB** <argument> - tests whether the string argument is empty.
-The conditional assembly statement, together with possible **ELSEIF** and **ELSE** statements, is shown in the following code.
+The conditional assembly statement, together with optional **ELSEIF** and **ELSE** statements, is shown in the following code.
 <code asm>
 IF expression1
@@ Line 216: / Line 243: @@
 All fields in a statement are optional. A statement can be composed of a label only (ended with a colon), an operation only (if it doesn't require operands), or a comment only. A few examples of proper statements are presented in the following code.
 <code asm>
-; name    ; operation ; operands ; comment
+; name ; operation ; operands ; comment
-cns_y      EQU         134       ; definition of a constant named cns_y with the value 134
+cns_y   EQU         134       ; definition of a constant named cns_y with the
+                              ;   value 134
-           .DATA                 ; operation only - directive to start data section
+        .DATA                 ; operation only - directive to start data section
-var_x      DB          123       ; definition of a variable named var_x with init value 123
+var_x   DB          123       ; definition of a variable named var_x with init
+                              ;   value 123
-           .CODE                 ; operation only - directive to start code section
+        .CODE                 ; operation only - directive to start code section
-begin:                           ; name only - label that represents an address
+begin:                        ; name only - label that represents an address
-           mov         rax, rbx  ; operation and corresponding operands
+        mov         rax, rbx  ; operation and corresponding operands
-                                 ; comment only statement
+                              ; comment only statement
-           END                   ; operation only - end of the source file
+        END                   ; operation only - end of the source file
 </code>

en/multiasm/papc/chapter_6_12.1763122806.txt.gz · Last modified: 2025/11/14 14:20 by ktokarz