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Tapejara
Journeyman III

Size Attribute of Count Register in LOOP Instruction

According to the AMD64 manuals:

"The size of the count register used (CX, ECX, or RCX) depends on the address-size attribute of the LOOP

cc instruction."





What does this mean? In 32-bit environments is this aways ECX?

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avk
Adept III

Size Attribute of Count Register in LOOP Instruction

AFAIK, in 32-bit environments, you can choose between the native 32-bit form and the legacy 16-bit form of the instruction:

32 bit form: 0E3h, <byte offset>

16 bit form: 67h, 0E3h, <byte offset>

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