+ l2×l3 + l3×l2 + l4×l1) = l0×l0 + 19×2×(l1×l4 + l2×l3) r0 := mul(l0, l0) r0 = addMul38(r0, l1, l4) r0 = addMul38(r0, l2, l3) // r1 = l0×l1 + l1×l0 + 19×(l2×l4 + l3×l3 + l4×l2) = 2×l0×l1 + 19×2×l2×l4 + 19×l3×l3 r1 := mul(l0*2, l1) r1 = addMul38(r1, l2, l4) r1 = addMul19(r1, l3, l3) // r2 = l0×l2 + l1×l1 + l2×l0 + 19×(l3×l4 + l4×l3) = 2×l0×l2 + l1×l1 + 19×2×l3×l4 r2 := mul(l0*2, l2) r2 = addMul(r2, l1, l1) r2 = addMul38(r2, l3, l4) // r3 = l0×l3 + l1×l2 + l2×l1 + l3×l0 + 19×l4×l4 = 2×l0×l3 + 2×l1×l2...