Added solution for determining the parity of a binary integral value.

Author: ScottFries

include/code_library/bitwise/parity.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+/**
+ * The parity of a binary word is 1 if the number of 1s in the word is odd; othersie it is 0.
+ * A common use case for parity checking is error detection, especially when transmitting data.
+ * https://en.wikipedia.org/wiki/Parity_bit
+ */
+
+#include <climits> // CHAR_BIT
+#include <type_traits>
+
+/**
+ * Determines the parity of a given binary integer value.
+ * Returns true if Parity is 1, or false if Parity is 0.
+ *
+ * Parity is determined by repeatedly performing an XOR operation on the upper half of the binary
+ * value against the lower half until we're left with a single bit that represents the parity.
+ *
+ * Note that the runtime speed of this can be improved (up to ~1.5x) by specializing the function
+ * on input type and unwinding the loop.
+ */
+template <typename T, typename = std::enable_if_t<std::is_integral_v<T>>>
+bool parity(T value)
+{
+    short bits = CHAR_BIT * sizeof(T);
+    while ((bits /= 2) >= 1)
+    {
+        value ^= value >> bits;
+    }
+    return value & 0b1;
+}

test/CMakeLists.txt

@@ -40,6 +40,22 @@ catch_discover_tests(
     .xml
 )
 
+add_executable(parity_tests "bitwise/parity_tests.cpp")
+target_link_libraries(parity_tests PRIVATE project_options project_warnings catch_main)
+catch_discover_tests(
+    parity_tests
+    TEST_PREFIX
+    "parity."
+    REPORTER
+    xml
+    OUTPUT_DIR
+    .
+    OUTPUT_PREFIX
+    "parity."
+    OUTPUT_SUFFIX
+    .xml
+)
+
 add_executable(has_function_tests "conditions/has_function_tests.cpp")
 target_link_libraries(has_function_tests PRIVATE project_options project_warnings catch_main)
 catch_discover_tests(

test/bitwise/parity_tests.cpp

@@ -0,0 +1,36 @@
+#include "code_library/bitwise/parity.hpp" 
+
+#include <catch2/catch.hpp>
+
+TEST_CASE("Parity of integral can be determined", "[parity]")
+{
+    SECTION("Parity of uint32_t")
+    {
+        uint32_t value1 = 0b1000'1000'1000'1000'1000'1000'1000'1000;
+        uint32_t value2 = 0b1000'0000'1000'1000'1000'1000'1000'1000;
+        uint32_t value3 = 0b1111'1111'1111'1111'1111'1111'1111'1111;
+        REQUIRE(!parity(value1));
+        REQUIRE(parity(value2));
+        REQUIRE(!parity(value3));
+    }
+
+    SECTION("Parity of an char8_t")
+    {
+        char8_t value1 = 0b1000'1000;
+        char8_t value2 = 0b1000'0000;
+        char8_t value3 = 0b1111'1111;
+        REQUIRE(!parity(value1));
+        REQUIRE(parity(value2));
+        REQUIRE(!parity(value3));
+    }
+
+    SECTION("Parity of an int64_t")
+    {
+        int64_t value1 = 0b100'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000;
+        int64_t value2 = 0b100'0000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000'1000;
+        int64_t value3 = 0b111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111;
+        REQUIRE(!parity(value1));
+        REQUIRE(parity(value2));
+        REQUIRE(parity(value3));
+    }
+}