Merge pull request #18 from KredeGC/checksum

Move checksum logic into trait

Author: KredeGC

README.md

@@ -35,6 +35,7 @@ Based on [Glenn Fiedler's articles](https://gafferongames.com/post/reading_and_w
   * [Half-precision float - half_precision](#half-precision-float---half_precision)
   * [Bounded float - bounded_range](#bounded-float---bounded_range)
   * [Quaternion - smallest_three\<Q, BitsPerElement\>](#quaternion---smallest_threeq-bitsperelement)
+  * [Checksum\<V\>](#checksumversion)
 * [Extensibility](#extensibility)
   * [Adding new serializables types](#adding-new-serializables-types)
   * [Unified serialization](#unified-serialization)
@@ -443,6 +444,27 @@ bool status_write = writer.serialize<smallest_three<quaternion, 12>>(in_value);
 bool status_read = reader.serialize<smallest_three<quaternion, 12>>(out_value);
 ```
 
+## Checksum\<Version\>
+A trait that creates a checksum based on the 32-bit number given.<br/>
+If the checksum that was written does not match when reading, it returns false.
+Must be called before anything else is serizalized, and again once everything is fully serialized.
+When reading you can omit the last serialize, as it is a noop.
+
+The call signature can be seen below:
+```cpp
+bool serialize<checksum<Version>>();
+```
+As well as a short example of its usage:
+```cpp
+bool status_write = writer.serialize<checksum<0x12345678>>();
+// Serialize some stuff...
+status_write = writer.serialize<checksum<0x12345678>>();
+
+bool status_read = reader.serialize<checksum<0x12345678>>();
+// Deserialize some stuff...
+status_read = reader.serialize<checksum<0x12345678>>(); // Last deserialize on read is optional (a noop)
+```
+
 # Extensibility
 The library is made with extensibility in mind.
 The `bit_writer<T>` and `bit_reader<T>` use a template trait specialization of the given type to deduce how to serialize and deserialize the object.

generate.bat

@@ -1,2 +1,2 @@
-call vendor\bin\premake\premake5.exe vs2019
+call vendor\bin\premake\premake5.exe vs2022
 pause

include/bitstream/bitstream.h

@@ -15,6 +15,7 @@
 // Traits
 #include "traits/array_traits.h"
 #include "traits/bool_trait.h"
+#include "traits/checksum_trait.h"
 #include "traits/enum_trait.h"
 #include "traits/float_trait.h"
 #include "traits/integral_traits.h"

include/bitstream/stream/bit_reader.h

@@ -106,35 +106,6 @@ namespace bitstream
 		*/
 		[[nodiscard]] uint32_t get_total_bits() const noexcept { return m_Policy.get_total_bits(); }
 
-		/**
-		 * @brief Reads the first 32 bits of the buffer and compares it to a checksum of the @p protocol_version and the rest of the buffer
-		 * @param protocol_version A unique version number
-		 * @return Whether the checksum matches what was written
-		*/
-		[[nodiscard]] bool serialize_checksum(uint32_t protocol_version) noexcept
-		{
-			BS_ASSERT(get_num_bits_serialized() == 0);
-
-			BS_ASSERT(can_serialize_bits(32U));
-
-			uint32_t num_bytes = (get_total_bits() - 1U) / 8U + 1U;
-			const uint32_t* buffer = m_Policy.get_buffer();
-
-			// Generate checksum to compare against
-			uint32_t generated_checksum = utility::crc_uint32(reinterpret_cast<const uint8_t*>(&protocol_version), reinterpret_cast<const uint8_t*>(buffer + 1), num_bytes - 4);
-
-			// Advance the reader by the size of the checksum (32 bits / 1 word)
-			m_WordIndex++;
-
-			BS_ASSERT(m_Policy.extend(32U));
-
-			// Read the checksum
-			uint32_t checksum = *buffer;
-
-			// Compare the checksum
-			return generated_checksum == checksum;
-		}
-
 		/**
 		 * @brief Pads the buffer up to the given number of bytes
 		 * @param num_bytes The byte number to pad to

include/bitstream/stream/bit_writer.h

@@ -126,46 +126,6 @@ namespace bitstream
 			return get_num_bits_serialized();
 		}
 
-		/**
-		 * @brief Instructs the writer that you intend to use `serialize_checksum()` later on, and to reserve the first 32 bits.
-		 * @return Returns false if anything has already been written to the buffer or if there's no space to write the checksum
-		*/
-		[[nodiscard]] bool prepend_checksum() noexcept
-		{
-			BS_ASSERT(get_num_bits_serialized() == 0);
-
-            BS_ASSERT(m_Policy.extend(32U));
-            
-			// Advance the reader by the size of the checksum (32 bits / 1 word)
-			m_WordIndex++;
-            
-            return true;
-		}
-
-		/**
-		 * @brief Writes a checksum of the @p protocol_version and the rest of the buffer as the first 32 bits
-		 * @param protocol_version A unique version number
-		 * @return The number of bytes written to the buffer
-		*/
-		uint32_t serialize_checksum(uint32_t protocol_version) noexcept
-		{
-			uint32_t num_bits = flush();
-
-			BS_ASSERT(num_bits > 32U);
-
-			// Copy protocol version to buffer
-			uint32_t* buffer = m_Policy.get_buffer();
-			*buffer = protocol_version;
-
-			// Generate checksum of version + data
-			uint32_t checksum = utility::crc_uint32(reinterpret_cast<uint8_t*>(buffer), get_num_bytes_serialized());
-
-			// Put checksum at beginning
-			*buffer = checksum;
-
-			return num_bits;
-		}
-
 		/**
 		 * @brief Pads the buffer up to the given number of bytes with zeros
 		 * @param num_bytes The byte number to pad to
@@ -338,7 +298,8 @@ namespace bitstream
 		 * @param writer The writer to copy into
 		 * @return Returns false if writing would overflow the buffer
 		*/
-		[[nodiscard]] bool serialize_into(bit_writer& writer) const noexcept
+		template<typename T>
+		[[nodiscard]] bool serialize_into(bit_writer<T>& writer) const noexcept
 		{
 			uint8_t* buffer = reinterpret_cast<uint8_t*>(m_Policy.get_buffer());
 			uint32_t num_bits = get_num_bits_serialized();

include/bitstream/traits/checksum_trait.h

@@ -0,0 +1,78 @@
+#pragma once
+#include "../utility/assert.h"
+#include "../utility/crc.h"
+#include "../utility/meta.h"
+#include "../utility/parameter.h"
+
+#include "../stream/serialize_traits.h"
+
+namespace bitstream
+{
+	/**
+	 * @brief Type for checksums
+	 * @tparam Version A unique version number
+	*/
+	template<uint32_t Version>
+	struct checksum;
+
+	/**
+	 * @brief A trait used to serialize a checksum of the @p Version and the rest of the buffer as the first 32 bits.
+	 * This should be called both first and last when reading and writing to a buffer.
+	 * @tparam Version A unique version number
+	*/
+	template<uint32_t Version>
+	struct serialize_traits<checksum<Version>>
+	{
+		constexpr static uint32_t protocol_version = utility::to_big_endian32_const(Version);
+		constexpr static uint32_t protocol_size = sizeof(uint32_t);
+
+		template<typename Stream>
+		typename utility::is_writing_t<Stream>
+		static serialize(Stream& writer) noexcept
+		{
+			if (writer.get_num_bits_serialized() == 0)
+				return writer.pad_to_size(4);
+			
+			uint32_t num_bits = writer.flush();
+
+			BS_ASSERT(num_bits >= 32U);
+
+			// Get buffer info
+			uint8_t* byte_buffer = writer.get_buffer();
+			uint32_t num_bytes = writer.get_num_bytes_serialized();
+
+			// Generate checksum of version + data
+			uint32_t generated_checksum = utility::crc_uint32(protocol_version, byte_buffer + protocol_size, writer.get_num_bytes_serialized() - protocol_size);
+
+			// Put checksum at beginning
+			uint32_t* buffer = reinterpret_cast<uint32_t*>(byte_buffer);
+			*buffer = utility::to_big_endian32(generated_checksum);
+
+			return true;
+		}
+
+		template<typename Stream>
+		typename utility::is_reading_t<Stream>
+		static serialize(Stream& reader) noexcept
+		{
+			if (reader.get_num_bits_serialized() > 0)
+				return true;
+			
+			BS_ASSERT(reader.can_serialize_bits(32U));
+
+			// Get buffer info
+			const uint8_t* byte_buffer = reader.get_buffer();
+			uint32_t num_bytes = (reader.get_total_bits() - 1U) / 8U + 1U;
+
+			// Generate checksum to compare against
+			uint32_t generated_checksum = utility::crc_uint32(protocol_version, byte_buffer + protocol_size, num_bytes - protocol_size);
+
+			// Read the checksum
+			uint32_t given_checksum;
+			BS_ASSERT(reader.serialize_bits(given_checksum, 32U));
+
+			// Compare the checksum
+			return generated_checksum == given_checksum;
+		}
+	};
+}

include/bitstream/utility/crc.h

@@ -2,6 +2,7 @@
 
 #include <array>
 #include <cstdint>
+#include <cstring>
 
 namespace bitstream::utility
 {
@@ -22,22 +23,15 @@ namespace bitstream::utility
 		return table;
 	}();
 
-	inline constexpr uint32_t crc_uint32(const uint8_t* bytes, uint32_t size)
+	inline uint32_t crc_uint32(uint32_t checksum, const uint8_t* bytes, uint32_t size)
 	{
 		uint32_t result = 0xFFFFFFFF;
 
-		for (uint32_t i = 0; i < size; i++)
-			result = CHECKSUM_TABLE[(result & 0xFF) ^ *(bytes + i)] ^ (result >> 8);
-
-		return ~result;
-	}
-
-	inline constexpr uint32_t crc_uint32(const uint8_t* checksum, const uint8_t* bytes, uint32_t size)
-	{
-		uint32_t result = 0xFFFFFFFF;
+		uint8_t checksum_table[4]{};
+		std::memcpy(&checksum_table, &checksum, sizeof(uint32_t));
 
 		for (uint32_t i = 0; i < 4; i++)
-			result = CHECKSUM_TABLE[(result & 0xFF) ^ *(checksum + i)] ^ (result >> 8);
+			result = CHECKSUM_TABLE[(result & 0xFF) ^ *(checksum_table + i)] ^ (result >> 8);
 
 		for (uint32_t i = 0; i < size; i++)
 			result = CHECKSUM_TABLE[(result & 0xFF) ^ *(bytes + i)] ^ (result >> 8);

include/bitstream/utility/endian.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "platform.h"
+
 #include <cstdint>
 
 #if defined(__cpp_lib_endian) && __cpp_lib_endian >= 201907L
@@ -63,23 +65,43 @@ namespace bitstream::utility
 #endif // defined(BS_LITTLE_ENDIAN)
     }
 
-    inline uint32_t endian_swap32(uint32_t value)
+    constexpr inline uint32_t endian_swap32_const(uint32_t value)
     {
-#if defined(_WIN32)
-        return _byteswap_ulong(value);
-#elif defined(__linux__)
-        return __builtin_bswap32(value);
-#else
         const uint32_t first = (value << 24) & 0xFF000000;
         const uint32_t second = (value << 8) & 0x00FF0000;
         const uint32_t third = (value >> 8) & 0x0000FF00;
         const uint32_t fourth = (value >> 24) & 0x000000FF;
 
         return first | second | third | fourth;
+    }
+
+    BS_CONSTEXPR inline uint32_t endian_swap32(uint32_t value)
+    {
+        if BS_CONST_EVALUATED()
+        {
+            return endian_swap32_const(value);
+        }
+        else
+        {
+#if defined(_WIN32)
+            return _byteswap_ulong(value);
+#elif defined(__linux__)
+            return __builtin_bswap32(value);
+#else
+            return endian_swap32_const(value);
 #endif // _WIN32 || __linux__
+        }
+    }
+
+    constexpr inline uint32_t to_big_endian32_const(uint32_t value)
+    {
+        if constexpr (little_endian())
+            return endian_swap32_const(value);
+        else
+            return value;
     }
 
-    inline uint32_t to_big_endian32(uint32_t value)
+    BS_CONSTEXPR inline uint32_t to_big_endian32(uint32_t value)
     {
         if constexpr (little_endian())
             return endian_swap32(value);

include/bitstream/utility/parameter.h

@@ -1,16 +1,11 @@
 #pragma once
 
 #include "assert.h"
+#include "platform.h"
 
 #include <utility>
 #include <type_traits>
 
-#ifdef __cpp_constexpr_dynamic_alloc
-#define BS_CONSTEXPR constexpr
-#else // __cpp_constexpr_dynamic_alloc
-#define BS_CONSTEXPR
-#endif // __cpp_constexpr_dynamic_alloc
-
 namespace bitstream
 {
 #ifdef BS_DEBUG_BREAK

include/bitstream/utility/platform.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include <type_traits>
+
+#if defined(__cpp_lib_is_constant_evaluated) && __cpp_lib_is_constant_evaluated >= 201811L
+#	define BS_CONST_EVALUATED() (std::is_constant_evaluated())
+#	define BS_CONSTEXPR constexpr
+#else // __cpp_lib_is_constant_evaluated
+#	define BS_CONST_EVALUATED() constexpr (false)
+#	define BS_CONSTEXPR
+#endif // __cpp_lib_is_constant_evaluated