In computer organization, instruction execution can vary between straight-line sequencing and branching. Straight-line sequencing refers to the sequential execution of instructions, one after another, without any jumps or conditional branches. On the other hand, branching involves changing the control flow of the program by executing instructions conditionally based on certain conditions or by explicitly jumping to different sections of the code.
Let’s outline the main differences in instruction execution between straight-line sequencing and branching using suitable examples:
Straight-Line Sequencing:
In straight-line sequencing, instructions are executed one after another, in the order they appear in the code. There are no jumps or branches to alter the normal flow of execution.
Example: Consider a simple C/C++ function that calculates the sum of two numbers:
int calculateSum(int a, int b) {
int sum = a + b;
return sum;
}
The corresponding assembly code for this function (assuming a simplified instruction set) might look like:
; Assembly code for calculateSum function
calculateSum:
ADD R1, R2, R3 ; Add the values of a (R2) and b (R3), and store the result in R1
RET ; Return from the function, with the result in R1
In this straight-line sequencing example, the assembly instructions are executed one by one without any jumps or branches.
Branching:
Branching involves changing the flow of execution based on certain conditions or explicit jump instructions. The processor evaluates conditions, such as comparisons between values, and determines whether to execute the next instruction in sequence or jump to a different location in the code.
Example: Consider a C/C++ function that compares two integers and returns the larger one:
int findMax(int a, int b) {
if (a > b) {
return a;
} else {
return b;
}
}
; Assembly code for findMax function
findMax:
CMP R2, R3 ; Compare the values of a (R2) and b (R3)
JGT greater ; Jump to "greater" if a > b
MOV R1, R3 ; If a <= b, move the value of b (R3) to R1
RET ; Return with the value in R1
greater:
MOV R1, R2 ; If a > b, move the value of a (R2) to R1
RET ; Return with the value in R1
The assembly code uses branching instructions. The CMP instruction compares the values of a and b, and then the JGT (Jump if Greater Than) instruction determines whether to jump to the “greater” label or not based on the result of the comparison. The jump changes the flow of execution, and the instructions after the label are only executed when the condition is true.
