Function TestGradualWindowByteIdentityAtFullRing

fbclock/daemon/math_test.go:155–184

TestGradualWindowByteIdentityAtFullRing locks the invariant that the new k(n) W expression reduces bit-for-bit to the legacy "mean(m, N) + 4.0 * stddev(m, N)" once the ring is full (n == N).

(t *testing.T)

// TestGradualWindowByteIdentityAtFullRing locks the invariant that the new k(n) W expression reduces
// bit-for-bit to the legacy "mean(m, N) + 4.0 * stddev(m, N)" once the ring is full (n == N).
func TestGradualWindowByteIdentityAtFullRing(t *testing.T) {
	cases := []struct {
		n      int
		legacy string
	}{
		{30, "mean(m, 30) + 4.0 * stddev(m, 30)"},
		{100, "mean(m, 100) + 4.0 * stddev(m, 100)"},
	}
	for _, tc := range cases {
		ms := make([]float64, tc.n)
		for i := range ms {
			ms[i] = 100 + float64(i%7) // varied so stddev(m) > 0
		}
		newExpr, err := prepareExpression(MathDefaultW)
		require.NoError(t, err)
		legacyExpr, err := prepareExpression(tc.legacy)
		require.NoError(t, err)
		// At the full ring the precomputed factor is exactly 4.0 (coverageZP), so the new scalar-k
		// expression must reduce bit-for-bit to the legacy "mean(m,N) + 4.0*stddev(m,N)".
		gotNew, err := newExpr.Evaluate(map[string]interface{}{
			"m": ms,
			"n": float64(tc.n),
			"k": coverageZP,
		})
		require.NoError(t, err)
		gotLegacy, err := legacyExpr.Evaluate(map[string]interface{}{"m": ms})
		require.NoError(t, err)
		require.Equal(t, gotLegacy, gotNew)
	}
}