h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Russian Peasant Multiplication - A22519226
Author: Icy North - U225620

This one's dedicated to SWL - I know how much he likes these.

Oh My Lord! I'm dylexic with numbers!

>>Go Forth and Multiply<<
I love that.
Glad you added the tables, they simplify things.

Thanks Bel,

My original choice didn't make it past the profanity filter.

I hope the tables make sense. This is something that's dead easy to explain on a blackboard, but it's less easy rendering it into a guide entry.

Well, I think I understood it all, and you know I'm not good at maths.

Yes, but it has to pass the SWL test before I'll be happy. It has to be entertainingly useless.

Oh, it it's that what you're waiting for, I could have told you, too.

I'm not in the habit of bumping PR entries, but are there any further comments?

I was half-expecting someone from the Maths Forum to rip it to shreds.

I think it might end a bit suddenly. Do you think it would benefit from a closing sentence to say why the computer's multiplication method is similar, or is this obvious?

Icy

I don't understand why you say that numbers in binary are generally stored in the reverse order to the way we would expect. I'd dispute this. When you store a number like 57 in the computer, it is stored as 8 independent bits, but it is completely arbitrary what way you choose to write this when you are talking about it. It is not in any particular order in the computer. Let's call the eight bits in the computer A, B, C, D, E, F, G and H. So the number is stored as A=0, B=0, C=1, D=1, E=1, F=0, G=0 and H=1. This could be written 00111001. Alternatively, we could label the bits the other way around and write it 10011100. Since the first of these corresponds to standard binary, it is the one that makes most sense and the only one I have ever seen in any book on computers, in the 29 years I have worked with them.

Thanks Gnomon,

If my memory hasn't failed me, then the ordering comes in when you talk about a byte being loaded into a register, and the meaning of standard assembler instructions like 'shift left' and 'shift right'. I'll try to find a link which confirms this...

Well, the first few sites I found support your view, Gnomon, so I'll go ahead and reverse the order. (I must have learned it using some non-standard version of assembler)

I'm pleased that this is the case - it makes the comparison far easier to follow.

OK, I think that's fixed. I've added leading zeroes for the contents of the computer registers, as I think it looks better in this configuration.

The very last number of the piece should be 1331 rather than 1131.

Sorry, it should be 1,311.

Don't tell me I reversed that one too

Nice one Icy - it might be clearer if you talk about 'rounding down' rather than ignoring fractions - but that might just be me.

I think "ignoring fractions" is clearer, myself.

Yes, I think I prefer to stick with 'ignoring fractions' too. I might round down decimals, I suppose, but I think they would have to be in the context.

I built a binary multiplier once as a uni exercise. Long time ago though; can't really remember the details.

Nice entry though. No comments