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Instruction Descriptions 4–49
4.6.1 Compare Byte
Format:
Operation:
FOR i FROM 0 TO 7
temp<8:0> ← 0 || Rav<i*8+7:i*8>} + {0 || NOT Rbv<i*8+7:i*8>} + 1
Rc<i> ← temp<8>
END
Rc<63:8> ← 0
Exceptions:
Instruction mnemonics:
Qualifiers:
Description:
CMPBGE does eight parallel unsigned byte comparisons between corresponding bytes of Rav
and Rbv, storing the eight results in the low eight bits of Rc. The high 56 bits of Rc are set to
zero. Bit 0 of Rc corresponds to byte 0, bit 1 of Rc corresponds to byte 1, and so forth. A result
bit is set in Rc if the corresponding byte of Rav is greater than or equal to Rbv (unsigned).
Notes:
The result of CMPBGE can be used as an input to ZAP and ZAPNOT.
To scan for a byte of zeros in a character string:
<initialize R1 to aligned QW address of string>
LOOP:
LDQ R2, 0(R1) ; Pick up 8 bytes
LDA R1, 8(R1) ; Increment string pointer
CMPBGE R31, R2,R3 ; If NO bytes of zero, R3<7:0>=0
BEQ R3, LOOP ; Loop if no terminator byte found
... ; At this point, R3 can be used to
; determine which byte terminated
CMPBGE Ra.rq,Rb.rq,Rc.wq
!Operate format
CMPBGE Ra.rq,#b.ib,Rc.wq
!Operate format
None
CMPBGE Compare Byte
None