Iron Curtain — Design Documentation

D009: Simulation — Fixed-Point Math, No Floats

Decision: All sim-layer calculations use integer/fixed-point arithmetic. Floats allowed only for rendering interpolation.

Rationale:

• Required for deterministic lockstep (floats can produce different results across platforms)
• Original Red Alert used integer math — proven approach
• OpenRA uses WDist/WPos/WAngle with 1024 subdivisions — same principle

P002 resolved: Scale factor = 1024 (matching OpenRA). Full type library (Fixed, WorldPos, WAngle), trig tables, CORDIC atan2, Newton sqrt, modifier arithmetic, and determinism guarantees: see research/fixed-point-math-design.md.