Branches and Jumps

Up to now: sequential instructions (strictly in order)

What other kinds of instructions do we need (think of kinds of C statements)?

selection (if/else, switch)

looping (for, while)

function calls

There is no such thing as selection or loop statement in machine language

only the evil G-word (goto)

In assembly language, change the order of execution with a branch or jump

branch: conditional (not always)

jump: unconditional (always)

What does it mean to branch?

Normally, PC <--- PC + 4 changes PC to point to next sequential instruction

Why add 4?

Because each instruction is 32 bits (4 bytes)

Jump: PC <--- target_location

Conditional branch ("branch"):

if (condition)

PC <--- target_location

else

PC <--- PC + 4

Unconditional branch ("jump"):

goto target_location