To understand the file "Program Flow Control in ARM Assembly Language" in a simplified way, imagine that a program is like a story you write for the computer, and you need to control the order of events based on conditions or repetition.
I will explain this file to you as if you have not understood anything before:
---
1. Types of Program Control
Every program contains three ways to control the flow of commands:
1. Sequential execution: executes commands one after the other.
2. Branching (if): executes certain commands if a condition is met.
3. Looping: repeats a set of commands until a certain condition is met.
---
2. Flags
During operations, the processor sets signals called "flags" to help in decision-making:
Z (Zero): equals 1 if the result is zero.
N (Negative): equals 1 if the result is negative.
C (Carry): used for unsigned operations (e.g., was there a carry?).
V (Overflow): did the value exceed the limit in signed numbers?
---
3. Comparisons
If you want to compare two numbers, you use:
CMP r0, r1 like r0 - r1, but do not save the result, just set the flags.
Then you use a command like BEQ (branch if equal), BNE (branch if not equal)...
---
4. Jump Commands (Branching)
B label: jump unconditionally.
BEQ label: jump if Z = 1 (result is zero).
BNE label: jump if Z = 0 (result is not zero).
BGE, BLT, BGT, BLE: all are used based on flags to control branching in signed conditions.
Example:
CMP r0, #0
BGE isPositive
MOV r1, 53932879799 ; if r0 < 0
B done