anchor.diff:      new CallInstruction(),
       new EnterFunctionInstruction(),
       new ReturnInstruction(),
  -    new TypeConversionInstruction(NumberType.uint8, NumberType.uint16),
  -    new TypeConversionInstruction(NumberType.uint16, NumberType.uint32),
  -    new TypeConversionInstruction(NumberType.uint32, NumberType.uint64),
       new TypeConversionInstruction(NumberType.sint8, NumberType.sint16),
       new TypeConversionInstruction(NumberType.sint16, NumberType.sint32),
       new TypeConversionInstruction(NumberType.sint32, NumberType.sint64),
  -    new TypeConversionInstruction(NumberType.uint16, NumberType.uint8),
  -    new TypeConversionInstruction(NumberType.uint32, NumberType.uint16),
  -    new TypeConversionInstruction(NumberType.uint64, NumberType.uint32),
       new TypeConversionInstruction(NumberType.uint32, NumberType.fp32),
       new TypeConversionInstruction(NumberType.sint32, NumberType.fp32),
       new TypeConversionInstruction(NumberType.fp32, NumberType.uint32),
  
positive.code: ///     double↦uint64
  ///     double↦sint64
  ///
  /// float width
  ///
  ///     float↦double
  ///     double↦float
  
negative.code: 
  /// Converts the top stack element between the specified types. Instead of
  /// reinterpreting the memory, the value is retained. For example, executing a
  /// type conversion `float↦uint32` on the value `1.0` yields `1` (which has
  /// a different bit pattern).
  ///
  /// The VM instruction set only supports a small subset of all to/from
  /// conversion pairs, because a large part can be constructed with these and
  /// other instructions:
  ///
  ///   * Casts between unsigned sizes can be done with `push<n> 0` and `pop n`,
  ///     where _n_ is the size difference.
  ///   * Reducing the size of signed integers can be done with `pop n`.
  ///   * Other casts not supported natively can be constructed in multiple steps;
  ///     for example `sint16↦float` can be implemented as
  ///     `sint16↦sint32, sint32↦float`.
  ///
  /// The implemented instances are signed integer width expansion between
  /// adjacent sizes,
  ///
  ///     sint8↦sint16
  ///     sint16↦sint32
  ///     sint32↦sint64
  ///
  /// int/float conversion between same-size types,
  ///
  ///     uint32↦float
  ///     sint32↦float
  