Not your average question...

[HarryW]

One reason this isn't your average C forum question is that it isn't really about C

This is closest really to assembler, so I've posted the thread there. I know you C programmer people tend to work in ASM quite often, and generally work at a lower level, so if you wouldn't mind, take a look would ya? Thanks

http://forums.vb-world.net/showthrea...threadid=43228

[HarryW]

In case anyone cares, this was my solution (couldn't get the simulator to work so I could test it) and I'm pretty sure it's right.

imul1	OPC=0x20					// Set OPC as a counter... OPC = 32
imul2	MAR=SP-1; rd					// Read first operand (second word on the stack)
imul3	H=TOS						// Operands are now in H and MDR, TOS freed to be accumulator
imul4	TOS=0						// Clear accumulator.  One 0 just handled.
imul5	MDR=MDR; SRA1; if (notLSB) goto imul17		// Check for 00, else carry on for 10
imul6	TOS=TOS-H; SRA1					// 10 - subtract multiplicand, start the shift
imul7	MDR=MDR; RROT					// Bitwise rotate on MDR, LSB has the next recode bit
imul8	OPC=OPC-1; if (Z) goto imul18			// Decrement the counter (OPC), if it's 0 then we've finished
imul9	MDR=MDR; SRA1; if (notLSB) goto imul14		// One 1 just handled, Check for 11/10 and skip one line if 10
imul10	TOS=TOS; SRA1; goto imul10			// 11 so start a shift then check for 10
imul11	TOS=TOS+H; SRA1					// 01 so add multiplicand then shift
imul12	MDR=MDR; RROT					// Bitwise rotate on MDR, LSB has the next recode bit
imul13	OPC=OPC-1; if (Z) goto imul19 else goto imul8	// Decrement counter.  Set JAM then set again if counter=zero
imul14	TOS=TOS; SRA1; goto imul15			// 00 so middle of string of 0s - keep shifting.
imul15	wr; goto imul20					// Write MDR to SP-1 (most significant word).  Skip next line.
imul16	wr						// Extra end-point, due to the way mic-1 conditional jumps work
imul17	MAR=SP						// Prepare to write LSW to top of stack.
imul18	MDR=TOS; wr; goto Main1				// Write least significant word to top of stack.  End instruction

That has to be the hardest piece of coursework I have ever had to do. Still, the lecturer said he would give people high marks (80%+) just for attempting this (I picked the hardest question ).