I installed that instruction. It was a slight variant of the PDP-6/10 rotate combined instruction, which rotated two adjacent accumulators as a single 72 bit word. The bit reverse version shifted one accumulator right and the other left, while passing the bit across the boundary. On Mar 28, 2014, at 9:03 PM, Eugene Salamin <gene_salamin@yahoo.com> wrote:
________________________________ From: Bill Gosper <billgosper@gmail.com> To: math-fun@mailman.xmission.com Sent: Friday, March 28, 2014 11:26 AM Subject: [math-fun] reversing the order of bits in a word
Probably the most important lesson in 7.1.3 is Knuth's strong advocacy of his MOR and MXOR (8×8 bitmatrix) instructions for inclusion in 64-bit order codes. Bit reversal takes two MORs. --rwg
As long as we are going to implement new instructions, better yet do a bit reverse. The MIT AI people hacked their PDP-10 to have bit reverse. Due to it's utility in FFT, I'm surprised that bit reverse is not a standard instruction.
-- Gene
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