Four cstage build+run rows for the fold-2a decompose step: issubnormalf64
across normals/zero/a constructed subnormal (f64frombits(1u64)), and
normalizef64 on both the normal path (n, 0) and the subnormal multiply
path (exp -52, result no longer subnormal). normalizef64's (f64, i64)
return rides the #102 16B-tuple-from-call receive; tuple-field f64s are
spilled to a let before any literal comparison to dodge the same
gate-blind XMM mis-load that holds back frexpf64 (see 952 header +
lib/math/floats.ww). Byte-id of a normalize-calling program is covered by
954's tuple-receive gate.
Hojun-Cho
b4752aad21