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Align TBYTE Variables on Quadword Aligned Addresses 55
22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
Example (Preferred):
Prolog:
PUSH EBP
MOV EBP, ESP
SUB ESP, SIZE_OF_LOCALS ;size of local variables
AND ESP, –8
;push registers that need to be preserved
Epilog: ;pop register that needed to be preserved
MOV ESP, EBP
POP EBP
RET
With this technique, function arguments can be accessed via
EBP, and local variables can be accessed via ESP. In order to
free EBP for general use, it needs to be saved and restored
between the prolog and the epilog.
Align TBYTE Variables on Quadword Aligned Addresses
Align variables of type TBYTE on quadword aligned addresses.
In order to make an array of TBYTE variables that are aligned,
array elements are 16-bytes apart. In general, TBYTE variables
should be avoided. Use double-precision variables instead.
C Language Structure Component Considerations
Structures (‘struct’ in C language) should be made the size of a
multiple of the largest base type of any of their components. To
meet this requirement, padding should be used where
necessary.
Language definitions permitting, to minimize padding,
structure components should be sorted and allocated such that
the components with a larger base type are allocated ahead of
those with a smaller base type. For example, consider the
following code: