Unusual behavor

Index > Macroinstructions > Unusual behavor

Author

Thread

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 15 Oct 2017, 14:44

Here is a simple example macro which converts a binary number to hexadecimal text.

Code:

macro bin2hex count, data
  local digit
  repeat count
    digit = (data shr ((count * 4 - 4) - (% - 1) * 4)) and 0x0F
    digit = digit + '0'
    if digit > '9'
      digit = digit + 7
    end if
    db digit
  end repeat
end macro

This:

Code:

  bin2hex 2, 0x55

creates this:

Code:

And this:

Code:

  bin2hex 2, (0x55 * 2)

creates this:

Code:

AA

However, this

Code:

  bin2hex 2, 0x55 * 2

creates this:

Code:

0A

fasmg and fasm.

_________________
Mike Gonta
look and see - many look but few see

https://mikegonta.com

15 Oct 2017, 14:44

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8359
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2017, 15:02

Remember that macro parameters are just a simple substitution of text. So if you put a parameter into an expression, you may end up with text that computes to something else than what you imagined:

Code:

digit = (0x55 * 2 shr ((2 * 4 - 4) - (1 - 1) * 4)) and 0x0F

If you need to use the value of a parameter in an expression, either enclose it with parentheses, or use a proxy variable.

15 Oct 2017, 15:02

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 15 Oct 2017, 15:23

Tomasz Grysztar wrote:

If you need to use the value of a parameter in an expression, either enclose it with parentheses, or use a proxy variable.

Code:

value = +K

What is the significance of the "+".

_________________
Mike Gonta
look and see - many look but few see

https://mikegonta.com

15 Oct 2017, 15:23

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8359
Location: Kraków, Poland

Tomasz Grysztar 15 Oct 2017, 15:25

Mike Gonta wrote:

Code:
value = +K    
What is the significance of the "+".

If the argument is a string, "+" converts it to number.

15 Oct 2017, 15:25

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum