From c1359a9543829370bb8f54938885cc52ac098666 Mon Sep 17 00:00:00 2001
From: Braxton Hall
Date: Sun, 23 Oct 2022 13:31:34 -0700
Subject: Create fib.ys

---
 adirar111/y86/fib.ys | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 adirar111/y86/fib.ys

(limited to 'adirar111/y86/fib.ys')

diff --git a/adirar111/y86/fib.ys b/adirar111/y86/fib.ys
new file mode 100644
index 0000000..156c1ae
--- /dev/null
+++ b/adirar111/y86/fib.ys
@@ -0,0 +1,56 @@
+# y86 implementation of
+# def fibonacci(n):
+# if n <= 1:
+# return n
+# return fibonacci(n-1) + fibonacci(n-2)
+
+.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:
-- 
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