Last updated April 10, 2022

Status: Tags: #cards/cmpt295/assembly Links: Central Processing Unit (CPU)

Condition Codes

Principles

CF - Carry Flag (for unsigned) ?

• indicates whether there is overflow

ZF - Zero Flag ?

• if result is 0

SF - Sign Flag (for signed) ?

• indicates whether result is a -ve number

OF - Overflow Flag (for signed) ?

• indicates whether result creaed +ve or -ve overflow

Changing

cmp* and test* set condition codes

Branching ?

• cmp* instruction ;; compare

- [![Image from Gyazo](https://i.gyazo.com/413b54162a61412135b65b301ce8b0d7.png)](https://gyazo.com/413b54162a61412135b65b301ce8b0d7)
- doesn't save result
- set condition codes based on src1-src2

• test* instruction (test)
  • 
  • result not stored in dest
  • set conditon codes based on src1 and src2
• $j^x$ instructions (jump)

$j^X$ use condition codes

?

Examples

function with if/else and return

?

• Code false condition first
  • If false, jump, else do true
  • have jump after true to prevent false from running

Backlinks

1

list from Condition Codes AND !outgoing(Condition Codes)

References:

Created:: 2022-02-05 20:58