; x86_64 linux nasm

struc Stack
  maxSize: resb 8
  currentSize: resb 8
  contents:
endStruc

section .data

soError: db "Stack Overflow Exception", 10
seError: db "Stack Empty Error", 10


section .text

createStack:
; IN: max number of elements (rdi)
; OUT: pointer to new stack (rax)
  push rdi
  xor rdx, rdx
  mov rbx, 8
  mul rbx
  mov rcx, rax
  mov rax, 12
  mov rdi, 0
  syscall
  push rax
  mov rdi, rax
  add rdi, rcx
  mov rax, 12
  syscall
  pop rax
  pop rbx
  mov qword [rax + maxSize], rbx
  mov qword [rax + currentSize], 0
  ret


push:
; IN: stack to operate on (stack argument), element to push (rdi)
; OUT: void
  mov rax, qword [rsp + 8]
  mov rbx, qword [rax + currentSize]
  cmp rbx, qword [rax + maxSize]
  je stackOverflow
  lea rsi, [rax + contents + 8*rbx]
  mov qword [rsi], rdi
  add qword [rax + currentSize], 1
  ret


pop:
; pop
; IN: stack to operate on (stack argument)
; OUT: element from stack top
  mov rax, qword [rsp + 8]
  mov rbx, qword [rax + currentSize]
  cmp rbx, 0
  je stackEmpty
  sub rbx, 1
  lea rsi, [rax + contents + 8*rbx]
  mov qword [rax + currentSize], rbx
  mov rax, qword [rsi]
  ret


; stack operation exceptions
stackOverflow:
  mov rsi, soError
  mov rdx, 25
  jmp errExit
stackEmpty:
  mov rsi, seError
  mov rdx, 18
errExit:
  mov rax, 1
  mov rdi, 1
  syscall
  mov rax, 60
  mov rdi, 1
  syscall