Assembler User Guide

Difference between operator precedence in armasm and C

ARM Compiler toolchain v5.02 for µVision Using the Assembler

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Difference between operator precedence in armasm and C

The assembler order of precedence is not exactly the same as in C.

For example, (1 + 2 :SHR: 3) evaluates as (1 + (2 :SHR: 3)) = 1 in armasm. The equivalent expression in C evaluates as ((1 + 2) >> 3) = 0.

ARM recommends you use brackets to make the precedence explicit.

If your code contains an expression that would parse differently in C, and you are not using the --unsafe option, armasm normally gives a warning:

A1466W: Operator precedence means that expression would evaluate differently in C

Table 33 shows the order of precedence of operators in armasm, and a comparison with the order in C (see Table 34).

From these tables:

The highest precedence operators are at the top of the list.
The highest precedence operators are evaluated first.
Operators of equal precedence are evaluated from left to right.

Table 33. Operator precedence in armasm

armasm precedence	equivalent C operators
unary operators	unary operators
`* / :MOD`:	`* / %`
string manipulation	n/a
`:SHL: :SHR: :ROR: :ROL:`	`<< >>`
`+ - :AND: :OR: :EOR:`	`+ - & \| ^`
`= > >= < <= /= <>`	`== > >= < <= !=`
:`LAND: :LOR: :LEOR:`	`&& \|\|`

Table 34. Operator precedence in C

C precedence
unary operators
`* / %`
`+ -` (as binary operators)
`<< >>`
`< <= > >=`
`== !=`
`&`
`^`
`\|`
`&&`
`\|\|`

Assembler User Guide

Difference between operator precedence in armasm and C

Difference between operator precedence in armasm and C

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