In ARM assembler the XOR method is actually equal in speed to the temporary variable method, and saves a register, and hence is a standard trick in any ARM programmers macro library. Eg :-

; Swap r0,r1 using r2 as temporary
; Takes 3 cycles

traditional
    MOV  r2, r0 ; r2 <- r0
    MOV  r0, r1 ; r0 <- r1
    MOV  r1, r2 ; r1 <- r2

; Swap r0, r1 with no extra register
; Takes 3 cycles

xor
    EOR  r0, r0, r1 ; r0 <- r0 ^ r1
    EOR  r1, r0, r1 ; r1 <- r0 ^ r1
    EOR  r0, r0, r1 ; r0 <- r0 ^ r1
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Apologies for non perl post, but perspective can be useful sometimes ;-)