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5.md

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+# ARM ISA
+
+## Syntax of Assembly
+
+* Label: Define a symbol
+```
+label:
+```
+
+* Instruction
+* Directive
+```
+.directive[;]
+```
+* macro_invocation
+
+## Assembly Expression
+
+Expressions consist of one or more integer literals or symbol references, combined using operators. Expression can be used as instruction operands or directive argument.
+
+Assembler evaluates all expression, which means **no rum-time evaluation**.
+
+Assembly Expressions are
+* Constnats
+* Symbol References
+* Operators
+  * Unary Operators: `+`, `-`, `~`
+  * Binary Operators: `+`, `-`, `*`, `/`, `%`
+  * Binary Logical Operators: `&&`, `||`
+  * Binary Bitwise Operators: `&`, `|`, `^`, `>>`, `<<`
+  * Binary Comparison Operators: `<`, `<=`, `>`, `>=`, `==`, `!=`