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|Home > Writing ARM Assembly Language > 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:
MACRO $label TestAndBranch $dest, $reg, $cc $label CMP $reg, #0 B$cc $dest MEND
The line after the
is the macro prototype statement. This defines
the name (
TestAndBranch) you use to invoke the
macro. It also defines parameters ($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 ... ... NonZero
After substitution this becomes:
test CMP r0, #0 BNE NonZero ... ... NonZero