### Auxiliary functions for operand stack manipulation

Source: https://www.w3.org/TR/wasm-core-1

Provides functions to push and pop operand types, including a version that checks against an expected type and handles unknown types. Includes accumulative functions for multiple operands.

```pseudocode
func push_opd(type : val_type | Unknown) =
  opds.push(type)

func pop_opd() : val_type | Unknown =
  if (opds.size() = ctrls[0].height && ctrls[0].unreachable) return Unknown
  error_if(opds.size() = ctrls[0].height)
  return opds.pop()

func pop_opd(expect : val_type | Unknown) : val_type | Unknown =
  let actual = pop_opd()
  if (actual = Unknown) return expect
  if (expect = Unknown) return actual
  error_if(actual =/= expect)
  return actual

func push_opds(types : list(val_type)) = foreach (t in types) push_opd(t)
func pop_opds(types : list(val_type)) = foreach (t in reverse(types)) pop_opd(t)

```

--------------------------------

### Auxiliary functions for control stack manipulation

Source: https://www.w3.org/TR/wasm-core-1

Provides functions to push and pop control frames, and to mark the current frame as unreachable. Popping verifies the operand stack matches the expected end types and height.

```pseudocode
func push_ctrl(label : list(val_type), out : list(val_type)) =
  let frame = ctrl_frame(label, out, opds.size(), false)
  ctrls.push(frame)

func pop_ctrl() : list(val_type) =
  error_if(ctrls.is_empty())
  let frame = ctrls[0]
  pop_opds(frame.end_types)
  error_if(opds.size() =/= frame.height)
  ctrls.pop()
  return frame.end_types

func unreachable() =
  opds.resize(ctrls[0].height)
  ctrls[0].unreachable := true

```