Jump to content
  • Advertisement


This topic is now archived and is closed to further replies.


asm help

This topic is 6261 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

when multiplying a binary number by (-1), in other word changing the sign the technique is NOT the number then ADD 1 to it. Why is ADD 1 needed to complete the process?

Share this post

Link to post
Share on other sites
That''s due to the way that signed numbers are stored. You probably know that unsigned chars are like this:

128 | 64 | 32 | 16 | 8 | 4 | 2 | 1

Signed chars are stored like this:

-128 | 64 | 32 | 16 | 8 | 4 | 2 | 1

Now, if I have 35, (32 + 2 + 1), if I NOT it I get (-128 + 64 + 16 + 8 + 4), but that''s only -36. To get -35, I have to add 1. So that''s why you need to add 1. The process is called the "two''s complement".

But wasn''t there an opcode to do that automatically?

Share this post

Link to post
Share on other sites

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!