.text
.global readchar

# local long result
# local char ch
# result = read(0, &ch, 1)
# if result != 0
#   return ch
# else
#   return -1
# endif
readchar:
  oldBP = 0
  retAddr = oldBP + 4
  result = oldBP - 4
  ch = result - 2

  pushl  %ebp
  movl   %esp,%ebp
  addl   $ch,%esp

  # result = read(0, &ch, 1)
  movl   $0,%ebx
  movl   $3,%eax
  movl   $1,%edx
  movl   %ebp,%ecx
  addl   $ch,%ecx
  int    $0x80
  movl   %eax,result(%ebp)

  #if result != 0
  cmpl   $0,result(%ebp)
  jz     eof
  movw   $0,%ax
  movb   ch(%ebp),%al
  jmp    end_of_sub
  # result != 0

eof:
  movw   $-1,%ax

end_of_sub:
  subl   $ch,%esp
  popl   %ebp
  ret