From 44eee260db098748a9700b90e7d9741a44b4a651 Mon Sep 17 00:00:00 2001
From: Ravenwater <theo@stillwater-sc.com>
Date: Wed, 13 Nov 2024 12:38:08 -0500
Subject: [PATCH] adding a generic find_msb() implementation for types that
 support bit patterns

---
 include/universal/utility/find_msb.hpp | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/include/universal/utility/find_msb.hpp b/include/universal/utility/find_msb.hpp
index 45c8d1f7..8943ca53 100644
--- a/include/universal/utility/find_msb.hpp
+++ b/include/universal/utility/find_msb.hpp
@@ -17,12 +17,22 @@ namespace sw { namespace universal {
 
 //static const unsigned int bval[] = { 0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4 };
 
+template<typename BitPatternType>
+constexpr unsigned find_msb(const BitPatternType& x) {
+	constexpr unsigned nbits = x.nbits;
+	for (unsigned i = 0; i < nbits; ++i) {
+		unsigned bitIndex = nbits - 1 - i;
+		if (x.test(bitIndex)) return bitIndex + 1;
+	}
+	return 0;
+}
+
 /// <summary>
 /// find most significant bit that is set
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(unsigned int x) {
+inline constexpr unsigned find_msb(unsigned int x) {
 	// find the first non-zero bit
 	unsigned int base = 0;
 	if (x & 0xFFFF0000) { base += 16; x >>= 16; }
@@ -41,7 +51,7 @@ inline constexpr unsigned int find_msb(unsigned int x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(unsigned long x) {
+inline constexpr unsigned find_msb(unsigned long x) {
 	// find the first non-zero bit
 	unsigned int base = 0;
 	if (x & 0xFFFF0000) { base += 16; x >>= 16; }
@@ -60,7 +70,7 @@ inline constexpr unsigned int find_msb(unsigned long x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(unsigned long long x) {
+inline constexpr unsigned find_msb(unsigned long long x) {
 	// find the first non-zero bit
 	unsigned int base = 0;
 	if (x & 0xFFFFFFFF00000000) { base += 32; x >>= 32; }
@@ -82,7 +92,7 @@ inline constexpr unsigned int find_msb(unsigned long long x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(signed char x) {
+inline constexpr unsigned find_msb(signed char x) {
 	// find the first non-zero bit
 	uint8_t tmp = uint8_t(x);
 	unsigned int base = 0;
@@ -100,7 +110,7 @@ inline constexpr unsigned int find_msb(signed char x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(short x) {
+inline constexpr unsigned find_msb(short x) {
 	// find the first non-zero bit
 	uint16_t tmp = uint16_t(x);
 	unsigned int base = 0;
@@ -119,7 +129,7 @@ inline constexpr unsigned int find_msb(short x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(int x) {
+inline constexpr unsigned find_msb(int x) {
 	// find the first non-zero bit
 	uint32_t tmp = uint32_t(x);
 	unsigned int base = 0;
@@ -139,7 +149,7 @@ inline constexpr unsigned int find_msb(int x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(long x) {
+inline constexpr unsigned find_msb(long x) {
 	// find the first non-zero bit
 	uint32_t tmp = uint32_t(x);
 	unsigned int base = 0;
@@ -160,7 +170,7 @@ inline constexpr unsigned int find_msb(long x) {
 /// </summary>
 /// <param name="x">value to scan</param>
 /// <returns> position of MSB that is set. LSB is defined to be at position 1, so no bits set returns 0</returns>
-inline constexpr unsigned int find_msb(long long x) {
+constexpr unsigned find_msb(long long x) {
 	// find the first non-zero bit
 	uint64_t tmp = uint64_t(x);
 	unsigned int base = 0;