/me notes that his quip about using a card sorter has, as usual, caused rampant pedanticism and topic drift, wonders why he bothers...
On Sat, Aug 31, 2013 at 10:55 AM, John Gilmore <[email protected]> wrote: > There is a qualitative difference between modern sorting technology > and the very simple 'logical' or lexicographic sorting operations > performed by a card sorter, one that Chris.Baicher properly emphasized > in an earlier post. They use data transformations to make it possible > for two keys to be compared using a single CLC[L]. (DB2 does similar > things too.) > > A single example will suffice here. The four signed binary-integer > storage formats and the nine floating-point storage formats all use > the twos-complement sign-representation, 0b for non-negative or 1b for > negative. The single-byte signed representation of -128 is thus > 11111111b and that of +127 is 01111111b. Lexicographically, the 2C > representation of -128 is greater than the 2C representation of +127. > This inconvenience can be dealt with in a constructed key that > concatenates 'mixed' data-type sort fields in at least two ways, e.g., > by complementing the high-order, leftmost bits of such quantities. > > Operations of this kind are well beyond the scope of card sorters. > Sorts have become black boxes. Few of their users know or care much > about what goes on inside them, and this is a pity because they embody > a lot of not at all obvious technology that is of considerable > interest. Much of it is or, better, would be useful elsewhere too. > > John Gilmore, Ashland, MA 01721 - USA > -- zMan -- "I've got a mainframe and I'm not afraid to use it"
