[Nottingham] A Little Coding Gem

[Martin]

Folks,

Fortune has just served up a little beauty for me just now:


   n = ((n >>  1) & 0x55555555) | ((n <<  1) & 0xaaaaaaaa);
   n = ((n >>  2) & 0x33333333) | ((n <<  2) & 0xcccccccc);
   n = ((n >>  4) & 0x0f0f0f0f) | ((n <<  4) & 0xf0f0f0f0);
   n = ((n >>  8) & 0x00ff00ff) | ((n <<  8) & 0xff00ff00);
   n = ((n >> 16) & 0x0000ffff) | ((n << 16) & 0xffff0000);

-- Yet another mystical 'C' gem. ...


Anyone like to guess or even work out what it does? :-> (Evil grin :-) )

More to the point, why would you want to do that?!


For example, the above reminds of a neat little trick in Z80 assembler
to use the "DAA" (Decimal Adjust Accumulator) to neatly encode/decode
ASCII hex characters...

	and  15
	add  a,90h
	daa
	adc  a,40h
	daa

The original intention for the DAA instruction was to support BCD
arithmetic...


Any other similar fun obscure beauties?

Cheers,
Martin


DAA:
http://z80-heaven.wikidot.com/instructions-set:daa

BCD:
http://en.wikipedia.org/wiki/Binary-coded_decimal

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