4.22 Test-and-branch macro example

You can use a macro to perform a test-and-branch operation.

In ARM code in any processor and in Thumb code in processors before ARMv6T2, a test-and-branch operation requires two instructions to implement.

You can define a macro such as this:

$label  TestAndBranch  $dest, $reg, $cc
$label  CMP     $reg, #0
        B$cc    $dest

The line after the MACRO directive is the macro prototype statement. This defines the name (TestAndBranch) you use to invoke the macro. It also defines parameters ($label, $dest, $reg, and $cc). Unspecified parameters are substituted with an empty string. For this macro you must give values for $dest, $reg and $cc to avoid syntax errors. The assembler substitutes the values you give into the code.

This macro can be invoked as follows:

test    TestAndBranch    NonZero, r0, NE

After substitution this becomes:

test    CMP     r0, #0
        BNE     NonZero
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