lib: bit manipulation functions

Functions for hiding all the masking and shifting required for accessing
bit ranges within an integer type.

Signed-off-by: Rick Altherr <kc8apf@kc8apf.net>
Signed-off-by: Tim 'mithro' Ansell <mithro@mithis.com>

lib/CMakeLists.txt

@@ -6,6 +6,11 @@ target_include_directories(libprjxray PUBLIC "include")
 target_link_libraries(libprjxray absl::strings)
 
 if (PRJXRAY_BUILD_TESTING)
+	add_executable(bit_ops_test bit_ops_test.cc)
+	target_link_libraries(bit_ops_test libprjxray gtest_main)
+	add_test(NAME bit_ops_test
+		 COMMAND bit_ops_test)
+
 	add_executable(memory_mapped_file_test memory_mapped_file_test.cc)
 	target_link_libraries(memory_mapped_file_test libprjxray gtest_main)
 	add_test(NAME memory_mapped_file_test

lib/bit_ops_test.cc

@@ -0,0 +1,43 @@
+#include <prjxray/bit_ops.h>
+
+#include <gtest/gtest.h>
+
+TEST(BitMaskTest, Bit0) {
+	uint32_t expected = prjxray::bit_mask<uint32_t>(0);
+	EXPECT_EQ(static_cast<uint32_t>(0x1), expected);
+}
+
+TEST(BitMaskTest, Bit3) {
+	uint32_t expected = prjxray::bit_mask<uint32_t>(3);
+	EXPECT_EQ(static_cast<uint32_t>(0x8), expected);
+}
+
+TEST(BitMaskRange, SingleBit) {
+	uint32_t expected = prjxray::bit_mask_range<uint32_t>(23, 23);
+	EXPECT_EQ(static_cast<uint32_t>(0x800000), expected);
+}
+
+TEST(BitMaskRange, DownToZero) {
+	uint32_t expected = prjxray::bit_mask_range<uint32_t>(7, 0);
+	EXPECT_EQ(static_cast<uint32_t>(0xFF), expected);
+}
+
+TEST(BitMaskRange, MiddleBits) {
+	uint32_t expected = prjxray::bit_mask_range<uint32_t>(18, 8);
+	EXPECT_EQ(static_cast<uint32_t>(0x7FF00), expected);
+}
+
+TEST(BitFieldGetTest, OneSelectedBit) {
+	uint32_t expected = prjxray::bit_field_get(0xFFFFFFFF, 23, 23);
+	EXPECT_EQ(static_cast<uint32_t>(1), expected);
+}
+
+TEST(BitFieldGetTest, SelectDownToZero) {
+	uint32_t expected = prjxray::bit_field_get(0xFFCCBBAA, 7, 0);
+	EXPECT_EQ(static_cast<uint32_t>(0xAA), expected);
+}
+
+TEST(BitFieldGetTest, SelectMidway) {
+	uint32_t expected = prjxray::bit_field_get(0xFFCCBBAA, 18, 8);
+	EXPECT_EQ(static_cast<uint32_t>(0x4BB), expected);
+}

lib/include/prjxray/bit_ops.h

@@ -0,0 +1,36 @@
+#ifndef PRJXRAY_LIB_BIT_OPS_H
+#define PRJXRAY_LIB_BIT_OPS_H
+
+namespace prjxray {
+
+template<typename UInt>
+constexpr UInt bit_mask(int bit) {
+	return (static_cast<UInt>(1) << bit);
+}
+
+template<typename UInt>
+constexpr UInt bit_sizeof() {
+	return sizeof(UInt) * 8;
+}
+
+template<typename UInt>
+constexpr UInt bit_all_ones() {
+	return ~static_cast<UInt>(0);
+}
+
+template<typename UInt>
+constexpr UInt bit_mask_range(int top_bit, int bottom_bit) {
+	return ((bit_all_ones<UInt>() >> (bit_sizeof<UInt>() - 1 - top_bit)) &
+		(bit_all_ones<UInt>() - bit_mask<UInt>(bottom_bit) +
+		 static_cast<UInt>(1)));
+}
+
+
+template<typename UInt>
+constexpr UInt bit_field_get(UInt value, int top_bit, int bottom_bit) {
+	return (value & bit_mask_range<UInt>(top_bit, bottom_bit)) >> bottom_bit;
+}
+
+}  // namespace prjxray
+
+#endif  // PRJXRAY_LIB_BIT_OPS_H