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S3C2440A RISC MICROPROCESSOR ARM INSTRUCTION SET
3-59
INSTRUCTION SET EXAMPLES
The following examples show ways in which the basic ARM920T instructions can combine to give efficient code.
None of these methods saves a great deal of execution time (although they may save some), mostly they just save
code.
USING THE CONDITIONAL INSTRUCTIONS
Using Conditionals for Logical OR
CMP Rn,#p ; If Rn=p OR Rm=q THEN GOTO Label.
BEQ Label
CMP Rm,#q
BEQ Label
This can be replaced by
CMP Rn,#p
CMPNE Rm,#q ; If condition not satisfied try other test.
BEQ Label
Absolute Value
TEQ Rn,#0 ; Test sign
RSBMI Rn,Rn,#0 ; and 2's complement if necessary.
Multiplication by 4, 5 or 6 (Run Time)
MOV Rc,Ra,LSL#2 ; Multiply by 4,
CMP Rb,#5 ; Test value,
ADDCS Rc,Rc,Ra ; Complete multiply by 5,
ADDHI Rc,Rc,Ra ; Complete multiply by 6.
Combining Discrete and Range Tests
TEQ Rc,#127 ; Discrete test,
CMPNE Rc,# " "-1 ; Range test
MOVLS Rc,# "" ; IF Rc<= "" OR Rc=ASCII(127)
; THEN Rc:= "."