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[solved] Assembler Question - Check if float is an integer?

 
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Marc71
How do I cheat?
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Joined: 20 Mar 2017
Posts: 4

PostPosted: Mon Apr 09, 2018 1:45 pm    Post subject: [solved] Assembler Question - Check if float is an integer? Reply with quote

Hi all,

funny problem: I have found a nice point in the sourcecode of a game where the gold-value is being read. But sometimes the same source jumps into reading the mana, too.

Original code:
Code:

520C07C1: 00 00              -  add [eax],al
520C07C3: 00 00              -  add [eax],al
520C07C5: 00 00              -  add [eax],al
520C07C7: 00 55 8B           -  add [ebp-75],dl
520C07CA: EC                 -  in al,dx
520C07CB: 83 EC 18           -  sub esp,18
520C07CE: D9 EE              -  fldz
520C07D0: D9 5D FC           -  fstp dword ptr [ebp-04]
520C07D3: 8B 45 08           -  mov eax,[ebp+08]
// ---------- INJECTING HERE ----------
520C07D6: D9 40 2C           -  fld dword ptr [eax+2C]
520C07D9: D9 5D FC           -  fstp dword ptr [ebp-04]
// ---------- DONE INJECTING  ----------
520C07DC: D9 45 FC           -  fld dword ptr [ebp-04]
520C07DF: C9                 -  leave
520C07E0: C3                 -  ret


Current injection is:
Code:

newmem:
  push eax
  add eax,2c
  mov [goldaddress],eax
  pop eax


So what I need is a way to decide: is [eax+2c] actually pointing to gold or mana? I found out: gold is always a plain integer number, stored as float, wheres mana is always a "real" float number.

Any ideas? Shocked

best regards,
Marc


Last edited by Marc71 on Tue Apr 10, 2018 8:44 am; edited 1 time in total
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ParkourPenguin
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Joined: 06 Jul 2014
Posts: 1919
Location: Arcadian Suburbia

PostPosted: Mon Apr 09, 2018 6:49 pm    Post subject: Reply with quote

Code:
label(code)
label(gold)
label(exit)

code:
  //...
  // st(0) contains floating point value being tested
  fld st(0)
  frndint
  fucomip st(1)
  jz gold
    // mana
    // code for mana here
    jmp exit
  gold:
    // code for gold here
  exit:
  //...

This probably isn't a good way of checking which address is being accessed, but I hope you learn something regardless.

_________________
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Marc71
How do I cheat?
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Joined: 20 Mar 2017
Posts: 4

PostPosted: Tue Apr 10, 2018 8:44 am    Post subject: Reply with quote

Many thanks!

You're right, it is definitively not the best way. Your code works, of course, but this only reduces the "switching" of addresses.

Tried the other code-sections which read the amount of gold, but guess what.... they are used for multiple values, too.

Have to find another way Smile
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