Opcodes in Hex

[n00b!]

Hi, how can I look up what Opcode stands for what number?
And how the reverse?

e.g. what is 0xDB as instruction, and what instruction stands for 0x43031488?

Thanks in Advance!

[hutch--]

noob,

You need the Intel manuals for hex opcodes. Just to make things complicated many mnemonics have multiple opcodes depending on the data size and if its a load or store.

Code Select Expand


mov eax, mem
is a different opcode to
mov mem, eax


[n00b!]

Hmm :-/
Where do I get these?

[cman]

I was reading a section in a assembly book about instruction encoding and wondered how most assembly language programmers know to calculate by hand instruction lengths when using instructions like "loop" ( where the jmp destination must be within -128 to 127 bytes from the current location of the "loop" instruction. Do most programmers use manuals to look up hex codes and calculate jump length this way or is an estimation used. Something I've wondered! Thanks for any input!

[hutch--]

cman,

Most people make a good guess and if it falls over they change it.

noob, go to the Intel site and download the manuals there. There is a link at the top of the forum.