22 August 2015, 12:37 | #241 | ||||
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I never started implementing LINK. Quote:
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Or one could extend the ld/st unit to support byte operations targeting the MSB of a register. Even further the ld/st unit could be extended to support loading/storing an arbitrary byte of a register. In a speed demon design changing the ld/st unit could lead to lower clock frequency as it touches a time critical part of the pipeline. If the same design then doesn't have proper microcode support then it is very hard to execute MOVEP at all. Not because it is really hard per se but because it is a very bad fit for the design. |
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22 August 2015, 20:09 | #242 | ||
son of 68k
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(and the removal of MOVEM.W in the coldfire doesn't look very smart either) Quote:
Too bad. Why did you stop doing your 68k implementation, btw ? Other 68k instructions need microcode as well. Oh, wait. They're the 020+ insns everyone removes too |
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23 August 2015, 03:43 | #243 | |
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1) Is there a logical encoding for it and is the encoding space taken worth the space used? 2) Is it consistent with the 68k? No other instructions allow sign extending a byte to a longword for addresses register destinations. Only allowing data register destinations for MOVEM.B really limits its value. 3) Would it be used enough to be worth implementing (cost benefit analysis)? Can compilers make good use of it? Does it save cycle or improve code density in practice? 4) Are there as many resources available for byte to longword extending as word to longword (less resources generally equates to less optimization possibilities)? The EA units allow only word to longword sign extension and allowing byte to longword extending in the EA may increase the mux size and slow the EA calculation. I doubt it would be a problem for most designs but wouldn't this introduce fixed point integers which aren't used anywhere else in the 68k? The range of fixed point integers is more limited than fp where the decimal point can float. These types of instructions generally take a lot of logic also. I can't say I've needed an integer square root very often either. |
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23 August 2015, 09:18 | #244 | |||||
son of 68k
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Note : my question was about how hard it was to do, i didn't want to discuss the usefulness. Quote:
Note : it would be zero-extended, not sign-extended (more useful on bytes). Quote:
Can compilers make good use for actual MOVEM.W ? You can study this, and thus you've got your answer for MOVEM.B as well (and you probably know that i don't care much about compilers). Quote:
Anyway if the alu can write An registers because they support more operations, then you have another place where to put that, and MVZ already provides the necessary operation. Quote:
I don't like fp for sqr. Does it give an exact result, or a rounded one ? My need is an exact result, i.e. the largest a such as a*a<=b. The range is better than with fp - src of full 64 bits and dst of 32. Btw If sqr is implemented as power of 1/2 then the precision is catastrophic. You need sqr any time you compute a distance. This can occur very often in a game AI, for example. Note : again, it was about how hard it would be to do, not to discuss the usefulness. I can do it, but if you really want to, it's time for a new thread (or a new PM) - as we're getting a little bit OT here |
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23 August 2015, 14:34 | #245 | ||||
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If I'll ever restart the design it would probably be translated to a VLIW type design with code morphing in Transmeta style. Quote:
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23 August 2015, 19:48 | #246 |
son of 68k
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