Conditional Execution
This time we are going to take a look at how to implement the loop in SHARC+ assembly. We will be using the following simple code as an example:
// Calculate the Fibonacci number Fn, n need to be at least 2
int fibonacci(int n) {
int a = 0, b = 1, f;
for (int i = 1; i < n; i++) {
f = a + b;
a = b;
b = f;
}
return f;
}
Normally, to implement it in assembly you would have code like this (RISC-V assembly for example):
li t0, 0 # a
li t1, 1 # b
li t3, 1 # loop counter
loop_start:
add t2, t0, t1
mv t0, t1
mv t1, t2
addi t3, t3, 1
blt t3, a0, loop_start
mv a0, t2
A similar thing could be implemented in SHARC+ as well. Let's take a look at the code first (note the code is fairly inefficient, and we will improve that gradually):
r2 = 1; // loop counter
r8 = 0;
r12 = 1;
loop_start:
r0 = r8 + r12;
r8 = r12;
r12 = r0;
r2 = r2 + 1;
comp(r2, r4);
if lt jump loop_start;
Aside from the syntax difference, one major difference is that SHARC+ uses flags to do the conditional jump, so a comparison instruction might be necessary before the condition. In this example, the loop counter is compared against the end condition. If the loop counter is less than (lt) the end condition, it jumps back to the beginning of the loop. If it is counting down, then we could use flags that directly compare the last result with zero. There are other conditional codes (and there complementary) available:
