text: define: DUK_USE_FUNCPTR_DEC16
  introduced: 1.1.0
  requires:
    - DUK_USE_FUNCPTR16
  default: false
  tags:
    - lowmemory
    - experimental
  description: >
    Use together with DUK_USE_FUNCPTR16 for arbitrary data pointer compression.
    DUK_USE_FUNCPTR_ENC16(udata,p) is a macro with a userdata and void ptr
    argument, and a duk_uint16_t return value.  The userdata argument is the
    heap userdata value given at heap creation.  Currently it is required that
    NULL encodes to integer 0, and integer 0 decodes to NULL.  No other pointer
    can be encoded to 0.
  