From dc86db5b87945a2bd7a710f1a0a79faff7ccd316 Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Mon, 28 Dec 2015 10:12:40 -0800
Subject: [PATCH] Reminder to my future self to not over-optimize complex
 conjugate multiply.

---
 firmware/common/utility_m4.hpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/firmware/common/utility_m4.hpp b/firmware/common/utility_m4.hpp
index e7d98e90f..2516f12a1 100644
--- a/firmware/common/utility_m4.hpp
+++ b/firmware/common/utility_m4.hpp
@@ -40,6 +40,9 @@ static inline complex32_t multiply_conjugate_s16_s32(const complex16_t::rep_type
 	// multiply: (a + bj) * (c + dj) = (ac - bd) + (bc + ad)j
 	// conjugate-multiply: (ac + bd) + (bc - ad)j
 	//return { a.real() * b.real() + a.imag() * b.imag(), a.imag() * b.real() - a.real() * b.imag() };
+	// NOTE: Did not use combination of SMUAD and SMUSDX because of non-saturating arithmetic.
+	// const int32_t r = __SMUAD(a, b);
+	// const int32_t i = __SMUSDX(b, a);
 	const int32_t rr = __SMULBB(a, b);
 	const int32_t ii = __SMULTT(a, b);
 	const int32_t r = __QADD(rr, ii);