From c76a7f434938458427616ea7d565000dffbd1a2e Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Wed, 19 Jun 2024 01:17:07 +0100
Subject: [PATCH] Allow GetBitMaskSC to be used with mask size equal to type
 size

---
 src/core/bitmath_func.hpp  |  9 ++++++---
 src/tests/bitmath_func.cpp | 16 ++++++++++++----
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/core/bitmath_func.hpp b/src/core/bitmath_func.hpp
index 5863cfe807..6af7a133d1 100644
--- a/src/core/bitmath_func.hpp
+++ b/src/core/bitmath_func.hpp
@@ -11,6 +11,7 @@
 #define BITMATH_FUNC_HPP
 
 #include <bit>
+#include <limits>
 #include <type_traits>
 
 /**
@@ -192,14 +193,16 @@ constexpr T ToggleBit(T &x, const uint8_t y)
  *
  * @param start The start bit
  * @param count The number of bits
- * @pre start + count < sizeof(T) * 8
  * @return The bit mask
  */
 template <typename T>
 constexpr T GetBitMaskSC(const uint8_t start, const uint8_t count)
 {
-	typename std::make_unsigned<T>::type mask = 1;
-	return (T)(((mask << count) - 1) << start);
+	using U = typename std::make_unsigned<T>::type;
+	constexpr uint BIT_WIDTH = std::numeric_limits<U>::digits;
+
+	U mask = ((static_cast<U>(1) << (count & (BIT_WIDTH - 1))) - 1) | (count >= BIT_WIDTH ? ~static_cast<U>(0) : 0);
+	return (T)(mask << start);
 }
 
 /**
diff --git a/src/tests/bitmath_func.cpp b/src/tests/bitmath_func.cpp
index 9b23684174..7f18a27661 100644
--- a/src/tests/bitmath_func.cpp
+++ b/src/tests/bitmath_func.cpp
@@ -71,8 +71,12 @@ TEST_CASE("SetBitIterator tests")
 
 TEST_CASE("GetBitMaskSC tests")
 {
-	CHECK(GetBitMaskSC<uint>(4, 4) == 0xF0);
-	CHECK(GetBitMaskSC<uint>(28, 4) == 0xF0000000);
+	CHECK(GetBitMaskSC<uint64_t>(36, 4) == 0xF000000000ULL);
+	CHECK(GetBitMaskSC<uint64_t>(60, 4) == 0xF000000000000000ULL);
+	CHECK(GetBitMaskSC<uint64_t>(0, 64) == 0xFFFFFFFFFFFFFFFFULL);
+	CHECK(GetBitMaskSC<uint32_t>(4, 4) == 0xF0);
+	CHECK(GetBitMaskSC<uint32_t>(28, 4) == 0xF0000000);
+	CHECK(GetBitMaskSC<uint32_t>(0, 32) == 0xFFFFFFFF);
 	CHECK(GetBitMaskSC<uint8_t>(7, 1) == 0x80);
 	CHECK(GetBitMaskSC<uint8_t>(0, 1) == 1);
 	CHECK(GetBitMaskSC<uint8_t>(0, 0) == 0);
@@ -81,8 +85,12 @@ TEST_CASE("GetBitMaskSC tests")
 
 TEST_CASE("GetBitMaskFL tests")
 {
-	CHECK(GetBitMaskFL<uint>(4, 7) == 0xF0);
-	CHECK(GetBitMaskFL<uint>(28, 31) == 0xF0000000);
+	CHECK(GetBitMaskFL<uint64_t>(36, 39) == 0xF000000000ULL);
+	CHECK(GetBitMaskFL<uint64_t>(60, 63) == 0xF000000000000000ULL);
+	CHECK(GetBitMaskFL<uint64_t>(0, 63) == 0xFFFFFFFFFFFFFFFFULL);
+	CHECK(GetBitMaskFL<uint32_t>(4, 7) == 0xF0);
+	CHECK(GetBitMaskFL<uint32_t>(28, 31) == 0xF0000000);
+	CHECK(GetBitMaskFL<uint32_t>(0, 31) == 0xFFFFFFFF);
 	CHECK(GetBitMaskFL<uint8_t>(7, 7) == 0x80);
 	CHECK(GetBitMaskFL<uint8_t>(0, 0) == 1);
 	CHECK(GetBitMaskFL<uint8_t>(3, 4) == 0x18);