An expression is a combination of symbols, numeric constants, and operators that uses standard arithmetic notation to yield a result. Expressions can be absolute or relocatable.
An expression is absolute when it is not subject to link-time relocation. An absolute expression may contain relocatable symbols, but they must reduce to pairs of the form (R 1 -R 2 ), where R 1 and R 2 are relocatable symbols defined in the same section in the current source file.
An expression is relocatable when it is subject to link-time relocation. A relocatable expression contains a relocatable symbol, and may contain an absolute expression. If a relocatable expression contains an absolute expression, it must be reducible to the form (R+K), where R is either a relocatable symbol defined in the current source file, or an undefined symbol, and K is an absolute expression. The address of the relocatable symbol is defined in link time.
The assembly operators indicate arithmetic or bitwise-logic calculations. Parentheses (()) determine the order in which calculations occur. The assembler evaluates all operators of the same precedence from left to right.
The assembler evaluates all operators according to their level of precedence. Table below lists the operator precedence rules from lowest to highest.
Precedence of Arithmetic and Bitwise Logic Operations |
||
Precedence |
Operator Symbol |
Operation |
|
0 (Low) |
+ - | ^ |
Addition Subtraction Bitwise inclusive OR Bitwise exclusive OR |
|
1 (Medium) |
* / % << >> & |
Multiplication Division Remainder Shift Left Arithmetic shift right Bitwise A ND |
|
2 (High) |
- ~ |
Unary negation Unary one’s complement |
Link-relocation operators generate link-relocation entries in expressions. See Link-relocation Operators for a list of the link-relocation operators.