Self-interpreter: while and loop (7)

Context

As a reminder, here is the final memory map

0 0 0 {instrs} 0 inst_ptr 0 0 0 inactive_flag direction_flag memory_ptr  0 0 0 0 0 {mem}

Let's now see how to implement '[' and ']'

Initial state

• Memory: see above
• Cursor: on instruction, next to inst_ptr
• Input: any

Process

• Common part 
• Access memory value - see previous post
• Copy memory value
• Move array back to initial position
•  While '['
• If copy is null
• increase inactive_flag
• If not: do nothing
• Loop ']'
• If copy is null: do nothing
• If not:
• decrease inactive_flag
• Set direction_flag to 1

Code for while

Access memory cell
>>>>[->+>+<<]>>[-<<+>>]<+[->>>>[>>]+>>[-]>[-<<+>>]<<<[<<]<<
]>>>>[>>]<
copy value
[->>+<<]>>[-<<+<[<<]<<+>>>>[>>]>]<<

move array back to initial position
<[[->>+<<]>[->>+<<]<<<]

check current memory value: do nothing if not null and move to corresponding loop otherwise
<+<[>-<[-]]>[-<
  if null (current position: next to memory_pointer)
  increase inactive_flag
  <<<+>>>
>]<
<<<<<

Code for loop

duplicate memory pointer and move to copy
>>>>[->+>+<<]>>[-<<+>>]<+
[
  -
  go to next memory cell
  >>>>[>>]+>>
  (re)init/copy memory indicator
  [-]>[-<<+>>]<<<[<<]<<
]
go to current memory cell
>>>>[>>]<
copy value
[->>+<<]>>[-<<+<[<<]<<+>>>>[>>]>]<<
move array back to initial position
<[[->>+<<]>[->>+<<]<<<]
check current memory value: do nothing if null and move to corresponding while otherwise
<<
[
  if not null (current position: next to memory_pointer)
  reset value
  [-]
  decrease inactive_flag and change direction_flag
  <<<->[-]+>>
]
<<<<<

Final state

• Memory: see above
• Cursor: on instruction, next to inst_ptr
• Input: unchanged
• Output: unchanged

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