[SPCA] Improve Stack section

semester3/spca/code-examples/01_asm/06_factorial.s

@@ -0,0 +1,12 @@
+factorial:
+    pushq %rbx              # Preserve frame pointer
+    movl %edi, %ebx     
+    movl $1, %eax
+    cmpl $1, %edi
+    jle .QUIT               # Base case reached: quit
+    leal -1(%rdi), %edi     # Prepare args for next function call
+    call factorial
+    imull %ebx, %eax        # Use result of function call
+.QUIT:
+    popq %rbx               # Restore frame pointer
+    ret

semester3/spca/code-examples/01_asm/07_swap_and_sum.s

@@ -0,0 +1,15 @@
+swap_and_sum:
+    movq    %rbx, -16(%rsp)     # Save %rbx
+    movslq  %esi,%rbx           # Save i    (and extend)
+    movq    %r12, -8(%rsp)      # Save %r12
+    movq    %rdi, %r12          # Save a
+    leaq    (%rdi,%rbx,8), %rdi # & a[i]   -> %rdi (arg 1)
+    subq    $16, %rsp           # Allocate stack frame
+    leaq    8(%rdi), %rsi       # & a[i+1] -> %rsi (arg 2)
+    call    swap                
+    movq    (%r12,%rbx,8), %rax # a[i]
+    addq    %rax, sum(%rip)     # sum += a[i]
+    movq    (%rsp), %rbx        # Restore %rbx
+    movq    8(%rsp), %r12       # Restore %r12
+    addq    $16, %rsp           # Deallocate stack frame
+    ret