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Index > Main > its time to float numbers

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Teehee



Joined: 05 Aug 2009
Posts: 568
Location: Brazil
Teehee
Hi.

I never worked with float numbers in assembly. I dunno where or how to start. Any link to article/tutorial is apreciated. Any quicky introduction here are welcome too.

Thanks in adv.

_________________
Sorry if bad english.
Post 30 May 2011, 14:21
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edfed



Joined: 20 Feb 2006
Posts: 4240
Location: 2018
edfed
start with some methodology, with FP, it is better to always comment the code.

like this:
Code:
        finit                   ; EMPTY
        fld1
        fimul dword[ss:esp+4]
;        fidiv dword[ss:esp]
        fadd [.angle]
        fstp [.angle]
        fldpi                   ; pi        ;
        fmul [.angle]           ; pi*angle  ;
        fdiv dword[ss:esp+8]    ; rad       ;
        fsincos                 ; cos       ; sin
        fld [.module]           ; module    ; cos       ; sin
        fimul dword[ss:esp+4]   ; ticks*mod ; cos       ; sin
        fidiv dword[ss:esp]     ; pixels    ; cos       ; sin
        fxch                    ; cos       ; pixels    ; sin
        fmul st0,st1            ; cos*pix   ; pixels    ; sin
        fadd [.x]               ; x         ; pixels    ; sin
        fst [.x]                ;
        fsub [.rayon]           ;
        fistp dword[eax+item.x] ; pixels    ; sin
        fmul st0,st1            ; pix*sin   ;
        fsubr [.y]              ; y
        fst [.y]                ;
        fsub [.rayon]           ;
        fistp dword[eax+item.y] ; EMPTY
    


look at some codes from djmauretto, he submitted a lot of good code with fpu.

and forget everything you know about general purpose assembly, fpu is a lot different, on many points.

there are effectivelly 8 registers, but they are 80 bits wide.
they are effectivelly 8, but are disposed as a stack.
st0 is the top of stack register.

the stack can be empty, full, trashed, etc...
don't mix MMX code and FPU code.
etc, etc...
a good tutorial is linked somewhere in the faq, i think it redirects to x86asm.net site.
Post 30 May 2011, 14:51
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Teehee



Joined: 05 Aug 2009
Posts: 568
Location: Brazil
Teehee
Then registers st0 to st7...

1. disposed as a stack? these registers live in CPU or memory? whats exactly "disposed as a stack" means: do i have an order to follow in order to access them? (i'm thinking on push/pop)
2. whats the difference among MMX & FPU?
3. what do you mean by empty, full, trashed..
4. why they're 80bits wide?

sorry Embarassed

_________________
Sorry if bad english.
Post 31 May 2011, 18:03
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mindcooler



Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden
mindcooler
Post 31 May 2011, 21:38
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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz
Post 31 May 2011, 21:53
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ctl3d32



Joined: 30 Dec 2009
Posts: 204
Location: Brazil
ctl3d32
Teehee wrote:
Then registers st0 to st7...

1. disposed as a stack? these registers live in CPU or memory? whats exactly "disposed as a stack" means: do i have an order to follow in order to access them? (i'm thinking on push/pop)
2. whats the difference among MMX & FPU?
3. what do you mean by empty, full, trashed..
4. why they're 80bits wide?

sorry Embarassed


It works like that:
Code:
fld dword[variable] ;loads variable to st0
fld dword[constant];loads constant to st0, and what was is st0 goes to st1
fmul st0,st1;multiplies st0 by st1 - st0 holds the result and st1 holds variable
fstp dword[value];store what's in st0 to value, pop(delete) what's in st0, and what's in st1 goes to st0
    


So, for example:
Code:
fld [a]
fld [b]
fld [c]
;gives st0 = c, st1 = b, st2 = a
fstp[d]
;gives st0 = b, st1 = a, st2 = empty
    


Like an HP calculator in RPN mode.
Post 01 Jun 2011, 00:01
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