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(nasm.info)Section 3.5

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3.5. Expressions
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   Expressions in NASM are similar in syntax to those in C.

   NASM does not guarantee the size of the integers used to evaluate
expressions at compile time: since NASM can compile and run on 64-bit
systems quite happily, don't assume that expressions are evaluated in
32- bit registers and so try to make deliberate use of integer
overflow. It might not always work. The only thing NASM will guarantee
is what's guaranteed by ANSI C: you always have _at least_ 32 bits to
work in.

   NASM supports two special tokens in expressions, allowing
calculations to involve the current assembly position: the `$' and `$$'
tokens.  `$' evaluates to the assembly position at the beginning of the
line containing the expression; so you can code an infinite loop using
`JMP $'. `$$' evaluates to the beginning of the current section; so you
can tell how far into the section you are by using `($-$$)'.

   The arithmetic operators provided by NASM are listed here, in
increasing order of precedence.

Section 3.5.1

`|': Bitwise OR Operator

Section 3.5.2

`^': Bitwise XOR Operator

Section 3.5.3

`&': Bitwise AND Operator

Section 3.5.4

`<<' and `>>': Bit Shift Operators

Section 3.5.5

`+' and `-': Addition and Subtraction Operators

Section 3.5.6

`*', `/', `//', `%' and `%%': Multiplication and Division

Section 3.5.7

Unary Operators: `+', `-', `~' and `SEG'