4.1.1. __align

The __align keyword instructs the compiler to align a variable on an n-byte boundary.

__align is a storage class modifier. It does not affect the type of the function.

Syntax

__align(n)

Where:

n

is the alignment boundary.

n can take the values 1, 2, 4, or 8.

The keyword __align comes immediately before the variable name.

Usage

__align(n) is useful when the normal alignment of the variable being declared is less than n. Eight-byte alignment can give a significant performance advantage with VFP instructions.

__align can be used in conjunction with extern and static.

Restrictions

Because __align is a storage class modifier, it cannot be used on:

  • types, including typedefs and structure definitions

  • function parameters.

You can only overalign. That is, you can make a two-byte object four-byte aligned but you cannot align a four-byte object at 2 bytes.

Example

__align(8) char buffer[128];  /* buffer starts on eight-byte boundary */

See also

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