define: DUK_OPT_HEAPPTR_DEC16
introduced: 1.1.0
requires:
  - DUK_OPT_HEAPPTR16
tags:
  - lowmemory
  - experimental
description: >
  Use together with DUK_OPT_HEAPPTR16 for heap pointer compression.
  DUK_OPT_HEAPPTR_DEC16(udata,x) is a macro with a userdata and duk_uint16_t
  argument, and a void ptr return value.  The userdata argument is the heap
  userdata value given at heap creation.