Shift right arithmetic

[daydreamerz]

I understand shift right arithmetic as shifting right and adding zeros in the places execept for the first place which gets the first bit of the original value as a sign bit. I'm not sure if this is right though. My professor gave me a program that is supposed to shift a value right 3 places and the original value is ffff0000 and the shifted value is ffffe000, and I don't think this is right with the definition I have of arithmetic shifts. I'm not sure if I'm not understanding the concept right, or if his program is just wrong.

[Zachm]

Well, this is exactly right.
The binary representative of your 32 bit value is:

1111 1111 1111 1111 0000 0000 0000 0000 Binary
  F    F    F    F    0    0    0    0     Hex

Shifting it right with an Arithmetic shift, the sign bit is duplicated and the result is:

1111 1111 1111 1111 1110 0000 0000 0000 Binary
  F    F    F    F    E    0    0    0     Hex

Regards,

Zach

[daydreamerz]

Thank you so much, I think I was just a little confused about what the shifts actually did.

[kahlinor]

This utility gives you a visual representation of what's going on with the SAR (and several other CPU) instructions. Check it out if you like. The small manual also has examples on several useful logical operations.