Data structure alignment: Difference between revisions

Revision as of 16:19, 5 June 2021

Revision as of 18:51, 5 June 2021

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For example, the padding to add to offset 0x59d for a 4-byte aligned structure is 3. The structure will then start at 0x5a0, which is a multiple of 4. However, when the alignment of ''offset'' is already equal to that of ''align'', the second modulo in ''(align - (offset mod align)) mod align'' will return zero, therefore the original value is left unchanged.

Since the alignment is by [[#Definitions|definition]] a power of two<ref>,{{efn|On modern computers where the target alignment is a power of two. This might not be true, for example, on a system using 9-bit bytes or 60-bit words.</ref>,}} the modulo operation can be reduced to a bitwise boolean AND operation.

The following formulas produce the aligned offset (where ''&'' is a [[bitwise AND]] and ''~'' a [[bitwise NOT]]):

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#define aligntonext(p, bits) alignto(((p) + (1 << bits) - 1), bits)

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==Notes==

{{notelist}}

==References==