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Software Demoscene Gift

Su personal ZX Spectrum radio

Últimos comentarios

VBI: pop hl, dude :))

Apass: The image is very well done, however I have a gripe with the code snippet :P.
<joke>
I see 2 possibilities - 1) the code performs what it was intended to do but then is inefficient or 2) the code has a bug, and could be re-written in a simpler fashion.
First - the code copies in RAM at consecutive addresses the value of the accumulator, however, the accumulator is copied from the same memory location as DE is not incremented.
So the code can be simplified as:
PUSH HL
LD B, 4
LD DE, CODE
LD HL, #FE00
LD A,(DE)
LOAD LD (HL), A
INC HL
DJNZ LOAD
Note the position of the LOAD label. The only thing that this code does extra is wasting some time (7T states which is not easily replaced by NOPs)

Second - the code forgot to increment DE:
PUSH HL 11T states
LD B, 4 7T states
LD DE, CODE 10T states
LD HL, #FE00 10T states
LOAD LD A,(DE) 7T states
LD (HL), A 7T states
INC HL 6T states
INC DE 6T states
DJNZ LOAD 13/8T states
In this case, the code execution lasts 11 + 7 + 10 + 10 + 4 x (7 + 7 + 6 + 6) + 3 x 13 + 8 = 189T states.
If the code is re-written as:
PUSH HL 11T states
LD BC, 4 10T states
LD DE, #FE00 10T states
LD HL, CODE 10T states
LDIR 21/16T states
In this case, the code execution lasts 11 + 10 + 10 + 10 + 3 x 21 + 16 = 120T States
Or even quicker (with the observation that BC pair is not preserved)
PUSH HL 11T states
LD DE, #FE00 10T states
LD HL, CODE 10T states
LDI 16T states
LDI 16T states
LDI 16T states
LDI 16T states
This lasts 11 + 10 + 10 + 4 x 16 = 95T states (half of the initial variant)
</joke>

Finally, given the code snippet, I don't understand why the Z80 is dizzy?
If the code would have ended with:
DI
HALT
... On a Speccy... that would indeed make the CPU dizzy.
And it would have been quite a pun for the demoparty...

Shuran33: Крутой сборник и оболочка приятная! Спасибо

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