Added description. x86 solutions for some problemsHEADmaster

1 files changed, 43 insertions, 0 deletions

diff --git a/02-Even-Fibonacci-numbers/asm/fib.asm b/02-Even-Fibonacci-numbers/asm/fib.asm
new file mode 100644
index 0000000..600a542
--- /dev/null
+++ b/02-Even-Fibonacci-numbers/asm/fib.asm
@@ -0,0 +1,43 @@
+; By considering the terms in the Fibonacci sequence whose values do not exceed four million,
+; find the sum of the even-valued terms.
+extern printf
+SECTION .data
+flag:   db  "%d",10,0           ; "%d\n\0"
+
+SECTION .text
+    global main    
+
+main:
+        push rbp                ; set up stack
+        mov rbp, rsp
+        mov rax, 1              ; start at fib_1 = 1
+        push rax                ; push first term of fib onto stack
+        mov r11, 0              ; sum = 0
+        mov r12, 0x3D0900       ; max = 4000000, this is < 2^64
+                                ; so we only need one register
+
+.loop   xor rdx, rdx            ; clear rdx (remainder) 
+        push rax                ; push current term on the stack
+        mov rcx, 2              ; divisible by 2
+        div rcx                 ; divide rdx:rax/rcx
+        cmp rdx, 0              ; compare only remainder
+        jz .sum                 ; if r = 0 , add to sum
+        jmp .next               ; else skip
+
+.sum    add r11, QWORD [rsp]    ; add latest term to sum register
+
+.next   mov rax, QWORD [rsp]    ; reload rax to current term                
+        add rax, QWORD [rsp+8]  ; add last term to current term
+        cmp rax, r12            ; while rax < r12 (4 mil)
+        jl .loop
+        
+        mov rdi, flag           ; arg 1 (format)
+        mov rsi, r11            ; arg 2 (value)
+        mov rax, 0		; no xmm registers
+        call printf wrt ..plt
+        mov rsp, rbp            ; reset to the top of the stack
+        pop rbp
+
+        mov rax, 0
+        ret
+