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4–24 Alpha Architecture Handbook
4.4 Integer Arithmetic Instructions
The integer arithmetic instructions perform add, subtract, multiply, signed and unsigned com-
pare, and bit count operations.
Count instruction (CIX) extension implementation note:
The CIX extension to the architecture provides the CTLZ, CTPOP, and CTTZ instructions.
Alpha processors for which the AMASK instruction returns bit 2 set implement these
instructions. Those processors for which AMASK does not return bit 2 set can take an
Illegal Instruction trap, and software can emulate their function, if required. AMASK is
described in Sections 4.11.1 and D.3.
The integer instructions are summarized in Table 4–5
There is no integer divide instruction. Division by a constant can be done by using UMULH;
division by a variable can be done by using a subroutine. See Section A.4.2.
Table 4–5: Integer Arithmetic Instructions Summary
Mnemonic Operation
ADD Add Quadword/Longword
S4ADD Scaled Add by 4
S8ADD Scaled Add by 8
CMPEQ Compare Signed Quadword Equal
CMPLT Compare Signed Quadword Less Than
CMPLE Compare Signed Quadword Less Than or Equal
CTLZ Count leading zero
CTPOP Count population
CTTZ Count trailing zero
CMPULT Compare Unsigned Quadword Less Than
CMPULE Compare Unsigned Quadword Less Than or Equal
MUL Multiply Quadword/Longword
UMULH Multiply Quadword Unsigned High
SUB Subtract Quadword/Longword
S4SUB Scaled Subtract by 4
S8SUB Scaled Subtract by 8