I have some trouble with TeX reading an undefined slot^Wfield.

Declarations are as follows:

    typedef union memory_word {
      int int_;
      glue_ratio gr;
      two_halves hh;
      four_quarters qqqq;
    } memory_word;

    static memory_word mem[mem_max - mem_min + 1];

TRACE

I arranged for all writes to 'mem' being logged, here is what I get.

:
:
mem[2238].hh.b1 = 0
mem[2238].hh.rh = 0
mem[2238].hh.rh = 2224
mem[2238].hh.lh = 7
mem[2238].hh.rh = 65535
mem[2238].gr = 2.39234          // .gr shares space with .int -> clobbered
-- mem[2238].int to be read.    // .int is undefined now.
:
:
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2021-07-26 --GB