; Fibonacci number generator using AMD64 assembly with Windows syscalls
; Uses lookup table for O(1) access
; Author: Assistant

.686p
.xmm
.model flat, C

include kernel32.inc
include user32.inc

includelib kernel32.lib
includelib user32.lib

.data
    ; Precomputed Fibonacci numbers (first 50)
    fib_table DWORD 1, 1, 2, 3, 5, 8, 13, 21, 34, 55
    fib_table DWORD 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765
    fib_table DWORD 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811, 514229, 832040
    fib_table DWORD 1346269, 2178309, 3524578, 5702887, 9227465, 14930352, 24157817, 39088169, 63245986, 102334155
    fib_table DWORD 165580141, 267914296, 433494437, 701408733, 1134903170, 1836311903
    
    ; Error messages
    msg_error DWORD 'Error: Index out of range', 0
    msg_success DWORD 'Fibonacci number: ', 0
    
    ; Console handles
    hStdOut HANDLE ?
    
.code

; Function to get Fibonacci number at index n (0-based)
; Input: EAX = index
; Output: EAX = Fibonacci number
get_fibonacci PROC
    ; Validate input
    cmp eax, 0
    jl invalid_input
    
    ; Check if index is within range (max 50)
    cmp eax, 49
    jg invalid_input
    
    ; Calculate address in table
    mov ebx, eax
    shl ebx, 2          ; Multiply by 4 (DWORD size)
    
    ; Load Fibonacci number from table
    mov eax, fib_table[ebx]
    ret
    
invalid_input:
    xor eax, eax        ; Return 0 for invalid input
    ret
get_fibonacci ENDP

; Function to print a number to console
print_number PROC
    ; Input: EAX = number to print
    push eax
    push ebx
    push ecx
    push edx
    
    ; Convert number to string and print
    mov ebx, 10
    mov ecx, 0          ; Digit count
    
    ; Special case for zero
    cmp eax, 0
    jne convert_loop
    mov ecx, 1
    jmp print_digits
    
convert_loop:
    cmp eax, 0
    je print_digits
    
    xor edx, edx        ; Clear high bits
    div ebx             ; Divide by 10
    push edx            ; Push remainder (digit)
    inc ecx             ; Increment digit count
    jmp convert_loop
    
print_digits:
    cmp ecx, 0
    je done_printing
    
    pop eax             ; Get digit back
    add eax, '0'        ; Convert to ASCII
    push eax
    
    ; Write character to console
    mov edx, esp
    push 1              ; Number of characters
    push edx            ; Address of character
    push hStdOut        ; Handle
    call WriteConsoleA
    
    add esp, 12         ; Clean up stack
    
    dec ecx
    jmp print_digits
    
done_printing:
    pop edx
    pop ecx
    pop ebx
    pop eax
    ret
print_number ENDP

; Main program entry point
main PROC
    ; Get console handle
    push -11            ; STD_OUTPUT_HANDLE
    call GetStdHandle
    mov hStdOut, eax
    
    ; Test Fibonacci numbers
    mov eax, 10         ; Get 11th Fibonacci number (0-indexed)
    call get_fibonacci
    
    ; Print result
    push eax
    call print_number
    add esp, 4
    
    ; Exit program
    push 0
    call ExitProcess
main ENDP

END main