pouët.net

"Description: This instruction incorrectly documented in Intel's materials. See description field. [src : http://asm.inightmare.org/opcodelst/index.php?op=AAA]"

; works physically for Intel(R) Core(TM)2 Duo
org 100h
esc:in al,60h
aaa
jz esc
ret

Also

Code:

in al,60h
das
jp loop


is 1 byte shorter than :

Code:

in al,60h
dec al
jnz loop


although it will exit on all keypresses and not just the <esc> key.
Abductee uses this.

In Intel Instruction Set Reference for DAA, DAS all flags except OF are actually defined.
added on the 2014-10-16 15:43:28 by frag

Just look at the code of "Hypnoteye"
http://www.pouet.net/prod.php?which=65604The tricks are :

1.) Horizontal segment shift (rrrola)
Adding 1 to the segment, adds 16 to the horizontal pixel offset. So, by adding n * 10 + 20
you center the image horizontally.

2.) The 0xCCCD trick (rrrola)
Multiplying DI (the current pixel position) with 0xCCCD, will put their respective X and Y
coordinates into DX and DL, AH.

For example (5,5) = (5*320+5) = (1605) = (0x645)
0x645 * 0xCCCD = 0x05040141

X 05.04
Y 04.01

Note : these values are now between -32768 and 32768 ;)

3.) Centering vertically
By a funny coincidence, if you start your code with "Push <word>" there is the opcode
0x68 at the start, which is [SI], if you don't touch that register. That's about the half of
the screen height, so you can subtract that from the Y coordinate, which safes a byte
over "sub dh,100" ;) For finding such coincidences, this map is very helpful
http://sparksandflames.com/files/x86InstructionChart.html
4.) Stack Adressing (rrrola and frag)
If you keep the register BX at zero, or make it be zero at the time you use this trick
you can efficiently get you registers on the FPU. That's possible because the stack
pointer SP is almost always the same on startup http://www.fysnet.net/yourhelp.htm
Just do a "pusha/popa" instead of several pushs/pops and adress via [BX-??]
See the stack order here : http://x86.renejeschke.de/html/file_module_x86_id_270.html
You also get easy access to "<byte> << 8" and "<byte> >> 8" terms, without the need
to actually perform something like "mov al,ah" or "shr ax,8" which saves (1-2) bytes.

5.) Constant Overlap
Instead of using 4 bytes precision for floats, use 2! append your constant right after
your code and leave the lower 2 bytes out. Calculate you hexadecimal representation
of the float HERE : http://www.h-schmidt.net/FloatConverter/IEEE754.html
That's almost always precise enough.
Advanced : Find places in your code, where the first two bytes of the constant already
exist, and refer to that places. Saves 4 bytes if done right. I pulled this of once in
Hypnoteye ;) (label mm) Again, to know where your desired numbers - or
good estimations of them - are use this map
http://sparksandflames.com/files/x86InstructionChart.html
Protip : Sometimes switching the sign of the constant helps ;)

6.) Black Color
You might know this one. If you want a black pixel, do a SALC. No matter what the flag
states are, AL is 0x00 or 0xFF afterwards, which both map to black when you use the
default palette. One byte is one byte! ^^

7.) Dithering to make smooth animations
This one is funky. Since "stosb" doesn't trigger any flags on overflow
(see here : http://x86.renejeschke.de/html/file_module_x86_id_306.html)
you need to add anything by yourself anyway. I found that two "inc di" work well
enough. It bascically draws every third pixel and then repeats this 2 times on
a shifted offset. After three frames, the zeroflag finally triggers and increments
the REAL framecounter by one. 2 bytes for triple diagonal interlacing, so to speak ^^

8.) Alternative palette generation
Something everbody should look at : the interrupt 10h version of setting colors
via OUT (0x3C8,0x3c9). Since it uses the interrupt 10h, you can save two bytes
here and weave the color generation into setting the video mode.
See : http://webpages.charter.net/danrollins/techhelp/0144.HTM

That's it for once. You should be able to integrate your raytracing loop into the
space between "pusha" and "popa". Loading the coordinates is already there,
(remember, between -32768 and +32768). Storing it back onto the stack, and
then getting it, is also there (to AL and CH, see, i already used an implicit shift
by 8 there). I will copy this on into the tiny tool box thread also, for everyone ;)

Greets, HellMood