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`----'`=-=' ' hjw
C Thaumaturgy Center
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Swapping values with XOR
#define SWAP(a, b) (((a) ^= (b)), ((b) ^= (a)), ((a) ^= (b)))
This is an old trick to exchange the values of the variables a and b
without using extra space for a temporary variable.
On January 20, 2005, Iain A. Fleming pointed out that the macro above
doesn't work when you swap with the same memory location, such as
SWAP(a[i], a[j]) with i == j. So if that may occur, consider defining
the macro as (((a) == (b)) || (((a) ^= (b)), ((b) ^= (a)), ((a) ^=
(b)))). On July 14, 2009, Hallvard Furuseth suggested that on some
machines, (((a) ^ (b)) && ((b) ^= (a) ^= (b), (a) ^= (b))) might be
faster, since the (a) ^ (b) expression is reused.
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