Compaq ECQD2KCTE manual To compare two character strings for greater/equal/less

To compare two character strings for greater/equal/less:

<initialize R1 to aligned QW address of string1> <initialize R2 to aligned QW address of string2> LOOP:

LDQ	R3,	0(R1)	; Pick up 8 bytes of string1
LDA	R1,	8(R1)	; Increment string1 pointer
LDQ	R4,	0(R2)	; Pick up 8 bytes of string2
LDA	R2,	8(R2)	; Increment string2 pointer
CMPBGE	R31,	R3, R6	; Test for zeros in string1
XOR	R3,	R4, R5	; Test for all equal bytes
BNE	R6,	DONE	; Exit if a zero found
BEQ	R5,	LOOP	; Loop if all equal
DONE: CMPBGE R31, R5, R5			;
...

;At this point, R5 can be used to determine the first not-equal

;byte position (if any), and R6 can be used to determine the

;position of the terminating zero in string1 (if any).

To range-check a string of characters in R1 for ‘0’ …‘9’:

LDQ	R2, lit0s	; Pick up 8 bytes of the character
		; BELOW ‘0’ ‘////////’
LDQ	R3, lit9s	; Pick up 8	bytes of the character
		; ABOVE ‘9’ ‘::::::::’
CMPBGE R2, R1, R4		; Some R4<i>=1 if character is LT ‘0’
CMPBGE R1, R3, R5		; Some R5<i>=1 if character is GT ‘9’
BNE	R4, ERROR	; Branch if some char too low
BNE	R5, ERROR	; Branch if some char too high

4–50Alpha Architecture Handbook