The following code is used to derive Fibonacci algorithm with this sequence: (0, 1, 1, 2, 3, 5, 8, 13, 21, …) where each number is “add” of two previous ones. int fib(int n){ if (n==0) return 0; else if (n == 1) return 1; else return fib(n−1) + fib(n−2); } Explain why the following RISC-V assembly code works, you need to explain all the details using the comments as hints?   # IMPORTANT! Stack pointer must remain a multiple of 16!!!!   addi x10,x10,8                # fib(8), you can change it fib: beq x10, x0, done             # If n==0, return 0 addi x5, x0, 1 beq x10, x5, done             # If n==1, return 1 addi x2, x2, -16              # Allocate 2 words of stack space sd x1, 0(x2)                  # Save the return address sd x10, 8(x2)                 # Save the current n addi x10, x10, -1             # x10 = n-1 jal x1, fib # fib(n-1) ld x5, 8(x2) # Load old n from the stack sd x10, 8(x2) # Push fib(n-1) onto the stack addi x10, x5, -2 # x10 = n-2 jal x1, fib # Call fib(n-2) ld x5, 8(x2) # x5 = fib(n-1) add x10, x10, x5 # x10 = fib(n-1)+fib(n-2)   # Clean up: ld x1, 0(x2) # Load saved return address addi x2, x2, 16 # Pop two words from the stack   done: jalr x0, 0(x1)

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The following code is used to derive Fibonacci algorithm with this sequence: (0, 1, 1, 2, 3, 5, 8, 13, 21, …) where each number is “add” of two previous ones.

int fib(int n){

if (n==0)

return 0;

else if (n == 1)

return 1;

else

return fib(n−1) + fib(n−2);

}

Explain why the following RISC-V assembly code works, you need to explain all the details using the comments as hints?

 

# IMPORTANT! Stack pointer must remain a multiple of 16!!!!

 

  1. addi x10,x10,8                # fib(8), you can change it
  2. fib:
  3. beq x10, x0, done             # If n==0, return 0
  4. addi x5, x0, 1
  5. beq x10, x5, done             # If n==1, return 1
  6. addi x2, x2, -16              # Allocate 2 words of stack space
  7. sd x1, 0(x2)                  # Save the return address
  8. sd x10, 8(x2)                 # Save the current n
  9. addi x10, x10, -1             # x10 = n-1
  • jal x1, fib # fib(n-1)
  • ld x5, 8(x2) # Load old n from the stack
  • sd x10, 8(x2) # Push fib(n-1) onto the stack
  • addi x10, x5, -2 # x10 = n-2
  • jal x1, fib # Call fib(n-2)
  • ld x5, 8(x2) # x5 = fib(n-1)
  • add x10, x10, x5 # x10 = fib(n-1)+fib(n-2)

 

  • # Clean up:
  • ld x1, 0(x2) # Load saved return address
  • addi x2, x2, 16 # Pop two words from the stack

 

  • done:
  • jalr x0, 0(x1)

 

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