Matrix transpose using lookup tables

Asked Mar 06 '12 at 17:00

Active Mar 06 '12 at 17:00

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I would like to transpose an array of 8 bytes using lookup tables unlike this post which transposes without using a lookup table: Bitwise transpose of 8 bytes

Even though the lookup table would be quite huge as the post mentions, I would like to know how to go about doing this.

edited May 23 '17 at 10:34

Community

asked Mar 06 '12 at 17:00

shyamsundar2007

2

The table would indeed be huge; approximately 100 million terabytes. Are you sure you want to do this? – Oliver Charlesworth Mar 06 '12 at 17:05
2

@OliCharlesworth "algorithms are for people who can't afford RAM" :D – tbert Mar 06 '12 at 17:16
There is a paragraph in Knuth-4 about word-wide bit operations. there might even be a simple arithmetic trick for this. (Knuth added a 8*8 bitwise multiply to MIX, IIRC) – wildplasser Mar 06 '12 at 17:38
@tbert "Buying RAM is for people who don't know how to write Algorithms" :-P – Agnius Vasiliauskas Mar 06 '12 at 17:50
@OliCharlesworth 100 million terabytes? I was thinking the lookup table would be something more like a 64*8 byte one as was mentioned in the link I posted... – shyamsundar2007 Mar 07 '12 at 00:57
There are 2^64 possible inputs... – Oliver Charlesworth Mar 07 '12 at 07:04

Matrix transpose using lookup tables

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