refactor: modernize pixel_sum to C++20 and migrate headers to .hpp

CMakeLists.txt

@@ -8,7 +8,7 @@ project(
 include(GNUInstallDirs)
 include(CTest)
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
@@ -20,15 +20,15 @@ if(PIXEL_SUM_ENABLE_SANITIZERS AND CMAKE_BUILD_TYPE STREQUAL "Debug")
 endif()
 
 set(PIXEL_SUM_PUBLIC_HEADERS
-    ${CMAKE_SOURCE_DIR}/include/pixel_sum/PixelSum.h)
+    ${CMAKE_SOURCE_DIR}/include/pixel_sum/pixel_sum.hpp)
 
 set(PIXEL_SUM_TEST_SUPPORT_HEADERS
-    ${CMAKE_SOURCE_DIR}/tests/support/Common.h
-    ${CMAKE_SOURCE_DIR}/tests/support/TestUtility.h
-    ${CMAKE_SOURCE_DIR}/tests/support/TimeUtility.h)
+    ${CMAKE_SOURCE_DIR}/tests/support/common.hpp
+    ${CMAKE_SOURCE_DIR}/tests/support/test_utility.hpp
+    ${CMAKE_SOURCE_DIR}/tests/support/time_utility.hpp)
 
 add_library(PixelSumLib
-    src/PixelSum.cpp
+    src/pixel_sum.cpp
     ${PIXEL_SUM_PUBLIC_HEADERS})
 
 target_include_directories(PixelSumLib
@@ -41,7 +41,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
 endif()
 
 add_executable(PixelSumTest
-    tests/PixelSumTest.cpp
+    tests/pixel_sum_test.cpp
     ${PIXEL_SUM_TEST_SUPPORT_HEADERS})
 
 target_link_libraries(PixelSumTest PRIVATE PixelSumLib)
@@ -58,8 +58,8 @@ find_program(CPPCHECK cppcheck)
 
 set(PIXEL_SUM_ALL_CPP
     ${PIXEL_SUM_PUBLIC_HEADERS}
-    ${CMAKE_SOURCE_DIR}/src/PixelSum.cpp
-    ${CMAKE_SOURCE_DIR}/tests/PixelSumTest.cpp
+    ${CMAKE_SOURCE_DIR}/src/pixel_sum.cpp
+    ${CMAKE_SOURCE_DIR}/tests/pixel_sum_test.cpp
     ${PIXEL_SUM_TEST_SUPPORT_HEADERS})
 
 if(CLANG_FORMAT)
@@ -78,7 +78,7 @@ endif()
 
 if(CLANG_TIDY)
     add_custom_target(tidy
-        COMMAND ${CLANG_TIDY} -p ${CMAKE_BINARY_DIR} ${CMAKE_SOURCE_DIR}/src/PixelSum.cpp ${CMAKE_SOURCE_DIR}/tests/PixelSumTest.cpp
+        COMMAND ${CLANG_TIDY} -p ${CMAKE_BINARY_DIR} ${CMAKE_SOURCE_DIR}/src/pixel_sum.cpp ${CMAKE_SOURCE_DIR}/tests/pixel_sum_test.cpp
         WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
         COMMENT "Running clang-tidy"
         VERBATIM)
@@ -87,7 +87,7 @@ endif()
 if(CPPCHECK)
     set(PIXEL_SUM_CPPCHECK_ARGS
         --enable=warning,style,performance,portability
-        --std=c++17
+        --std=c++20
         --language=c++
         --inline-suppr)
 

README.md

@@ -1,6 +1,6 @@
 # PixelSum
 
-A tiny C++17 library that builds summed-area tables (integral images) so rectangular queries over pixel buffers are O(1). It supports 8- and 16-bit pixels via a templated `PixelSum<T, S>` that stores both the raw pixels and two integral images: one for sums and one for non-zero counts.
+A tiny C++20 library that builds summed-area tables (integral images) so rectangular queries over pixel buffers are O(1). It supports 8- and 16-bit pixels via a templated `PixelSum<T, S>` that stores both the raw pixels and two integral images: one for sums and one for non-zero counts.
 
 ## Features
 - Constant-time sum, average, non-zero count, and non-zero average for any axis-aligned window
@@ -25,7 +25,7 @@ cmake --build build --parallel
 
 ## Usage
 ```cpp
-#include <pixel_sum/PixelSum.h>
+#include <pixel_sum/pixel_sum.hpp>
 
 std::vector<std::uint8_t> pixels(width * height, 128);
 PixelSumU8 ps(pixels.data(), width, height);
@@ -65,4 +65,4 @@ GitHub Actions (`.github/workflows/ci.yml`) runs:
 
 ## Notes
 - Dimensions are limited to 4096 x 4096 to keep intermediate sums within `uint32_t` for 8-bit pixels; switch to `PixelSumU16` for larger ranges or higher bit depth.
-- The minimal test harness in `tests/PixelSumTest.cpp` exercises edge cases and can be extended with additional `TEST` blocks.
+- The minimal test harness in `tests/pixel_sum_test.cpp` exercises edge cases and can be extended with additional `TEST` blocks.

include/pixel_sum/PixelSum.h → include/pixel_sum/pixel_sum.hpp

@@ -1,16 +1,19 @@
 #pragma once
 
+#include <cstddef>
 #include <cstdint>
-#include <utility>
+#include <span>
 #include <vector>
 
 template <typename T, typename S>
 class PixelSum {
-    static constexpr int MAX_WIDTH = 4096;
-    static constexpr int MAX_HEIGHT = 4096;
+    static constexpr int kMaxWidth = 4096;
+    static constexpr int kMaxHeight = 4096;
 
 public:
     explicit PixelSum(const T* buffer, int width, int height);
+    explicit PixelSum(std::span<const T> buffer, int width, int height);
+
     ~PixelSum() = default;
     PixelSum(const PixelSum&) = default;
     PixelSum(PixelSum&&) noexcept = default;
@@ -25,31 +28,18 @@ class PixelSum {
     explicit operator bool() const noexcept;
 
 private:
-    int width_ { 0 };
-    int height_ { 0 };
-
-    // pixel data
-    std::vector<T> pixel_data_ {};
+    int width_{0};
+    int height_{0};
 
-    // sparse matrix for existent flags
-    std::vector<S> nonzero_data_ {};
+    std::vector<T> pixel_data_{};
+    std::vector<S> nonzero_data_{};
+    std::vector<S> summed_data_{};
 
-    // each pixel represents the cumulative sum of corresponding input pixel with
-    // all pixels above and to the left of input pixel.
-    std::vector<S> summed_data_ {};
-
-    void swap(int& x0, int& y0, int& x1, int& y1) const;
-    bool clampBound(int& x0, int& y0, int& x1, int& y1) const;
-    [[nodiscard]] S getSummedArea(const std::vector<S>& data, int x0, int y0, int x1, int y1) const;
+    static void normalizeBounds(int& x0, int& y0, int& x1, int& y1);
+    [[nodiscard]] bool clampBounds(int& x0, int& y0, int& x1, int& y1) const;
+    [[nodiscard]] static std::size_t indexOf(int x, int y, int width) noexcept;
+    [[nodiscard]] S getSummedArea(std::span<const S> data, int x0, int y0, int x1, int y1) const;
 };
 
 using PixelSumU8 = PixelSum<std::uint8_t, std::uint32_t>;
 using PixelSumU16 = PixelSum<std::uint16_t, std::uint64_t>;
-
-template <typename T>
-inline void swap_if_a_greater_than_b(T& a, T& b)
-{
-    if (a > b) {
-        std::swap(a, b);
-    }
-}