Merge pull request #6 from adirar111/main

edits to `fib.s`

1 files changed, 61 insertions, 0 deletions

diff --git a/entries/adirar111/y86/fib.s b/entries/adirar111/y86/fib.s
new file mode 100644
index 0000000..8aa62d2
--- /dev/null
+++ b/entries/adirar111/y86/fib.s
@@ -0,0 +1,61 @@
+# y86 implementation of
+#
+# def fibonacci(n):
+#     if n <= 1:
+#         return n
+#     return fibonacci(n-1) + fibonacci(n-2)
+#
+# run it:
+#  * https://www.students.cs.ubc.ca/~cs-313/simulator/?arch=y86&impl=seq
+#  * https://www.eecs.yorku.ca/~jonatan/simulator/?arch=y86&impl=seq
+
+.pos 0
+main:
+irmovq stack, %rsp # initialize stack pointer
+irmovq $13, %rdi # %rdi = n
+call fib # fib(n)
+halt
+
+
+fib:
+irmovq $2, %rsi
+irmovq $1, %rdx
+rrmovq %rdi, %rcx
+rrmovq %rdi, %r8
+
+subq %rsi, %rcx # %rcx = n-2
+subq %rdx, %r8 # %r8 = n-1
+jle base # goto base if n <= 1
+
+recursed:
+# save to stack
+pushq %r8 # %r8 = n-1
+
+# recurse
+rrmovq %rcx, %rdi # %rdi = n-2
+call fib # fib(n-2)
+
+# restore from stack
+popq %r8 # %r8 = n-1
+
+# save to stack
+pushq %rax # %rax = fib(n-2)
+
+# recurse
+rrmovq %r8, %rdi # %rdi = n-1
+call fib # fib(n-1)
+
+# restore from stack
+popq %r10 # r10 = fib(n-2)
+
+addq %r10, %rax # %rax = fib(n-2) + fib(n-1)
+jmp end
+
+base:
+rrmovq %rdi, %rax # return n
+
+end:
+ret
+
+.pos 0x1000
+stack: