Difference between revisions of "Floating-point Opcodes"
From SizeCoding
(Created page with " The FPU offers a lot of operations not available to classic x86 CPU, like <code>SIN</code>, <code>COS</code>, <code>TAN</code>, <code>EXP</code> and so on. Usage and communic...") |
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Revision as of 12:18, 15 August 2016
The FPU offers a lot of operations not available to classic x86 CPU, like SIN, COS, TAN, EXP and so on. Usage and communication with the FPU is a bit iuncommon and takes a bit to get used to. It's recommended to read the creation of the snippet we want to modify first, this is how it looks like originally :
cwd ; "clear" DX for perfect alignment
mov al,0x13
X: int 0x10 ; set video mode AND draw pixel
mov ax,cx ; get column in AH
add ax,di ; offset by framecounter <-- REPLACE THIS WITH FPU CODE
xor al,ah ; the famous XOR pattern
and al,32+8 ; a more interesting variation of it
mov ah,0x0C ; set subfunction "set pixel" for int 0x10
loop X ; loop 65536 times
inc di ; increment framecounter
in al,0x60 ; check keyboard ...
dec al ; ... for ESC
jnz X ; rinse and repeat
ret ; quit program
and this is how it looks if we replace the instruction with FPU code :
cwd ; "clear" DX for perfect alignment
mov al,0x13
X: int 0x10 ; set video mode AND draw pixel
mov ax,cx ; get column in AH
fninit ; init FPU first
mov [si],ax ; write first addend to a memory location
fild word [si] ; F(pu) I(nteger) L(oad)D a WORD from memory location to the FPU stack
mov [si],di ; write second addend to a memory location
fiadd word [si] ; Directly add the word in the memory location to the top FPU stack
fist word [si] ; F(pu) I(nteger) ST(ore) the result into a memory location
mov ax,[si] ; Get the word from the memory location into AX
xor al,ah ; the famous XOR pattern
and al,32+8 ; a more interesting variation of it
mov ah,0x0C ; set subfunction "set pixel" for int 0x10
loop X ; loop 65536 times
inc di ; increment framecounter
in al,0x60 ; check keyboard ...
dec al ; ... for ESC
jnz X ; rinse and repeat
ret ; quit program
(explanation follows, dinner first ^^)
