| Author | Message | Time |
|---|---|---|
| Maddox | Basically, I just want to know the difference. | February 25, 2004, 2:15 AM |
| K | This reference always helps me: http://202.114.22.131/mirrors/www_litespeed_org/Tutorials/Drme2.htm [quote]LEA means Load Effective Address. Syntax: LEA destination,source Desination can be any 16 bit register and the source must be a memory operand (bit of data in memory). It puts the offset address of the source in the destination. [/quote] MOV is pretty self explanatory. | February 25, 2004, 2:59 AM |
| Maddox | [quote author=K link=board=7;threadid=5444;start=0#msg45910 date=1077677971] This reference always helps me: http://202.114.22.131/mirrors/www_litespeed_org/Tutorials/Drme2.htm [quote]LEA means Load Effective Address. Syntax: LEA destination,source Desination can be any 16 bit register and the source must be a memory operand (bit of data in memory). It puts the offset address of the source in the destination. [/quote] MOV is pretty self explanatory. [/quote] My question really was mean to be "how does lea relate to mov?" which was indicated by the "vs." Thanks for the reference, although I wish it was in alphabetical order. Have you ever seen LEA AX,[SI]+7 before? I'm pretty sure this is the same thing as lea ax, [si+7]. And isn't that the same as mov ax, si add ax, 7 It looks like lea is just there to make the code smaller by taking out all the additional arithmetic instructions to the address that would be required with mov. | February 25, 2004, 6:09 AM |
| Adron | Yes, LEA is there to let you use the address calculation units to calculate something and store the result in a register. It was probably originally intended for calculating things like [BX + SI + 47], but since you can now address with any register, it has turned into a generic quick expression evaluator instruction. You can do addition of up to two registers, and a constant. You can also scale one of the registers with a small value. | February 25, 2004, 11:05 AM |