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Borsuc



Joined: 29 Dec 2005
Posts: 2466
Location: Bucharest, Romania
Borsuc
bitshifter wrote:
Now... process 4 byte chunks without jumping.
Kinda useless since the max 32-bit integer size is just 10 decimal characters.

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Post 07 Dec 2009, 21:27
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
Quote:

Now... process 4 byte chunks without jumping.

Wouldn't I just,
Code:
;eax = current set of chars
;ebx = offset
;ecx = total
str_to_int:
xor eax, eax
xor ebx, ebx
xor ecx, ecx
@@:
mov eax, [str + ebl]
add ebl, 4
cmp eal, 0
je @f
cmp eah, 0
je @f
;I don't know how to check in the upper half of eax
sub eax, '0000'
imul ecx, 1000
add ecx, eax
jmp @b
@@:
mov [int], ecx
retn    

Or do you mean process the whole thing without jumping.
Would this work?
Post 08 Dec 2009, 00:13
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Tyler, supposing you fix those unexistent registers it will still not work. For instance lets suppose EAX is '1234', when you substract '0000' it will be 1*2^24 + 2*2^16 + 3*2^8 + 4*2^0 (i.e. 16,909,060) which is a number much bigger than 1234 and then you'll multiply it by 1000 which will make it way much bigger.

To solve this problem you'll need to either learn MMX (or SSE), or use some trick to process the characters in parallel. (Don't bother for now, besides, it is not clear if you'll actually get better performance)
Post 08 Dec 2009, 00:46
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
Borsuc wrote:


bitshifter wrote:

Now... process 4 byte chunks without jumping.


Kinda useless since the max 32-bit integer size is just 10 decimal characters.

I was thinking the same.
LocoDelAssembly wrote:

unexistent registers

What nonexistent regs? As for it not working, I totally agree, I had the concept completely wrong.
Post 08 Dec 2009, 01:50
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
There is no ebl, eal and eah registers, I guess you mean bl, al, and ah which them do exist. But then there is another problem, you can't use [str+bl], not only because "str" is a reserved symbol, but also because you can't use 8-bit registers for addressing.
Post 08 Dec 2009, 02:00
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
@LocoDelAssembly: I learned that you could access the lower halves of e(a-d)x like they were (a-d)x in my very early asm research. It was a tutorial I dled from some obscure website, apparently I should reconsider my sources. This was before I found Fasm, of course. Smile
btw, did you know Fasm is underlined as misspelled, that's messed up! Laughing
Post 08 Dec 2009, 03:40
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kohlrak



Joined: 21 Jul 2006
Posts: 1421
Location: Uncle Sam's Pad
kohlrak
Ok, your sources aren't completely wrong.

Firstly, the registers are all swapped. Because of this, bit 7 is the leftmost bit in ALL sizes of registers (i forget whether this is called big endian or little endian...). Now, with that in mind, an excerpt from my AFS project:

Code:
;+----------EAX----------+
;|     AX    |  unnamed  |
;|  AL | AH  |  unnamed  |
;+-----------------------+    


Note that is just 1 register.

Edit: The reason i depicted the register like this makes it easier to understand that "dd 0x01234567" is the same as "db 0x67, 0x45, 0x23, 0x01." This is important to remember and not to screw up.


Last edited by kohlrak on 08 Dec 2009, 19:23; edited 1 time in total
Post 08 Dec 2009, 19:18
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Borsuc



Joined: 29 Dec 2005
Posts: 2466
Location: Bucharest, Romania
Borsuc
AL is the lowest byte though, and AX the lowest word. You can't access the higher words or bytes directly.

Also kohlrak that diagram is confusing, it should be reversed. After all, "shifting right" by 24 shifts the highest byte towards AL... which should be on the right.
Post 08 Dec 2009, 19:20
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Ups I messed up with endianness too, with Tyler's method the actual value for string '1234' without the multiplication part would be 67,305,985, not 16,909,060.
Post 08 Dec 2009, 20:08
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kohlrak



Joined: 21 Jul 2006
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kohlrak
Now you see why i made that confusing diagram. I'd rather have not had to, but as you see, it's necessary. Laughing
Post 08 Dec 2009, 20:19
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edfed



Joined: 20 Feb 2006
Posts: 4237
Location: 2018
edfed
a very little idea.
use macro to make a prefix.

for exemple, force access to upper words and bytes of registers.

example:
Code:

heax  mov bl,al   ;will use al as a byte from hword

    

hreg in general to access any wanted register upper word.

transparentlly making:
ROR %reg,16
%inst %reg1,%reg
ROR %reg,16


or maybe a more complex thing like adding hax,hal,hah as upper part in instrutions,and macro will make the right stuff.
Post 08 Dec 2009, 21:04
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Tyler



Joined: 19 Nov 2009
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Location: NC, USA
Tyler
Borsuc wrote:

AL is the lowest byte though, and AX the lowest word. You can't access the higher words or bytes directly.

This was my understanding. I was just messed up in the fact I thought ax and eax were separate. That's why I thought I had to use the "e" in,
I wrote:

Code:
add ebl, 4 
    

Post 08 Dec 2009, 22:19
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Tyler



Joined: 19 Nov 2009
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Tyler
I figured out the first part of my question(with help, of course), but does anyone have any light to shed on integer to string?
Post 10 Dec 2009, 03:41
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
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LocoDelAssembly
Post 10 Dec 2009, 03:52
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kohlrak



Joined: 21 Jul 2006
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kohlrak
Integer to string? Divide by 10, add '0.' Be sure to go backwords though. Perhaps using the direction flag and the stosb function.
Post 10 Dec 2009, 03:52
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Borsuc



Joined: 29 Dec 2005
Posts: 2466
Location: Bucharest, Romania
Borsuc
Take the remainder of the division by 10 and add '0' and output that, then use the divided number (not remainder) to continue to next loop. And yes you have to do it backwards.

Division by constants can be converted to multiplications by "magic numbers" (much faster, muls compared to divs, but it requires some math to get those magic numbers to multiply with). One method is to use fixed-point to find out the 'reciprocal' (in integers) of the 10 constant, multiply by that, shift appropriately (truncates result), then multiply by 10 (via 'lea' is faster, see my code on this topic about ascii to int, same principle) and subtract the difference between original and this one (truncated) yields the remainder.

Of course it's actually better to get the remainder directly with the multiplication but it's a bit more advanced so I'll leave it to you to research it yourself.

Here's a fixed point article:

http://x86asm.net/articles/fixed-point-arithmetic-and-tricks/index.html

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Post 10 Dec 2009, 19:52
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Tyler wrote:
I figured out the first part of my question(with help, of course), but does anyone have any light to shed on integer to string?


See above, FASM IDE sources, and here:

http://board.flatassembler.net/topic.php?t=8670
Post 11 Dec 2009, 01:28
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
DOS386 wrote:


Tyler wrote:

I figured out the first part of my question(with help, of course), but does anyone have any light to shed on integer to string?



See above, FASM IDE sources, and here:



It's not that I'm too lazy to read it, it's that I don't understand it. I read through "PARSER.INC." It's just so massive that I never found what I was looking for.
Post 11 Dec 2009, 03:50
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DOS386



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Posts: 1901
DOS386
Post 11 Dec 2009, 10:40
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