Be quiet, NaN

[Albert Chan]

I was adding a feature to my old luajit 1.1.8, having randomseed() return its state.
(So that I can save it and restore later ...)

I had patched luajit using xoroshiro128+.
With 128 bits state, my first thought were to return 2 64-bits IEEE double.
(luajit (still) does not support 64-bits integer)

But, if the returned double happens to be signaling NaN, it change the bits, and turn it quiet.

gcc:1> union {double d; uint64_t u;} h
gcc:2> h.u = 0x7ff0000000000001ULL /* signaling NaN */
gcc:3> printf("%I64x", h.u)
7ff0000000000001
gcc:4> h.d = h.d /* just copied itself change the bits ! */
gcc:5> printf("%I64x", h.u)
7ff8000000000001

The fix is hard, see In which the CPU changes my data under my nose

---

I gave up 2 IEEE double approach, and return 4 32-bits integers.

Below is the example that tripped my 2 IEEE double approach.
Last 64 bits = 7ff4d423272049a1, silently converted to 7ffc ...

lua> randomseed(599)
1122989783       -1462116390       2146751523       656427425

lua> state = { randomseed() }            -- save state
lua> random(), random(), random()
0.2792170183740439       0.4552087223210315       0.9415057196559153
lua> ; randomseed(unpack(state))       -- restore state
lua> random(), random(), random()
0.2792170183740439       0.4552087223210315       0.9415057196559153