Single-header patcher for IPS. UPS and BPS files

hips.hpp

#pragma once
#include <algorithm>
#include <array>
#include <climits>
#include <cstdio>
#include <cstring>
#include <type_traits>
#include <utility>
#include <vector>

namespace Hips {
	using u8 = std::uint8_t;
	using u16 = std::uint16_t;
	using u32 = std::uint32_t;
	using u64 = std::uint64_t;
	using usize = std::size_t;

	using s8 = std::int8_t;
	using s16 = std::int16_t;
	using s32 = std::int32_t;
	using s64 = std::int64_t;

	enum class PatchType : u32 {
		IPS,
		UPS,
		BPS,
	};

	enum class Result : u32 {
		Success = 0,
		InvalidPatch,
		UnknownFormat,
		SizeMismatch,
		ChecksumMismatch,
	};

	namespace Detail {
		// Read "size" bytes, returning 0 if we're going to go out of bounds
		template <typename T = u64, usize size>
		T readBE(const u8* data, usize& offset, usize patchSize) {
			static_assert(std::is_integral<T>() && sizeof(T) >= size);

			offset += size;
			if (offset > patchSize) {
				// We're going to go out of bounds, return 0
				return T(0);
			}

			T ret = T(0);
			int shift = 0;
			// Read byte-by-byte
			for (int i = 0; i < size; i++) {
				ret |= T(data[offset - (i + 1)]) << shift;
				shift += CHAR_BIT;
			}

			return ret;
		}

		template <typename T = u64, usize size>
		T readLE(const u8* data, usize& offset, usize patchSize) {
			static_assert(std::is_integral<T>() && sizeof(T) >= size);

			offset += size;
			if (offset > patchSize) {
				// We're going to go out of bounds, return 0
				return T(0);
			}

			T ret = T(0);
			int shift = (size - 1) * 8;
			// Read byte-by-byte
			for (int i = 0; i < size; i++) {
				ret |= T(data[offset - (i + 1)]) << shift;
				shift -= CHAR_BIT;
			}

			return ret;
		}

		// Formats like UPS and BPS	use run-length encoded integers
		// Regrettably, handling anything > 64 bits is not easy, or particularly worth it
		// Until files start being larger than 18 exabytes that is
		template <typename T = u64>
		T readRunLength(const u8* data, usize& offset, usize patchSize) {
			u64 ret = 0;
			u64 shift = 1;

			while (true) {
				const u64 byte = readLE<u64, 1>(data, offset, patchSize);
				ret += (byte & 0x7F) * shift;

				// If the msb is set then the encoding ends on this byte
				if (byte & 0x80) {
					break;
				}

				shift <<= 7;
				ret += shift;
			}

			return T(ret);
		}

		static u32 crc32(const u8* data, usize length, u32 crc = 0) {
			// 8-bit CRC table
			static constexpr u32 crcTable[] = {
				0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E,
				0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB,
				0xF4D4B551, 0x83D385C7, 0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8,
				0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,
				0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59, 0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599,
				0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106,
				0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433, 0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB,
				0x086D3D2D, 0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
				0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65, 0x4DB26158, 0x3AB551CE, 0xA3BC0074,
				0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5,
				0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F, 0x5EDEF90E,
				0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
				0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27,
				0x7D079EB1, 0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0,
				0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1,
				0xA6BC5767, 0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
				0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92,
				0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F,
				0x72076785, 0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4,
				0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777, 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,
				0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D,
				0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9, 0xBDBDF21C, 0xCABAC28A,
				0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37,
				0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
			};

			crc = ~crc;
			for (usize i = 0; i < length; i++) {
				const u8 byte = data[i];
				crc = crcTable[(crc ^ byte) & 0xFF] ^ (crc >> 8);
			}

			return ~crc;
		}
	}  // namespace Detail

	namespace IPS {
		static constexpr usize headerSize = 5;
		// Need at least 5 (header) + 3 (EOF) bytes to be a valid IPS patch
		static constexpr usize minimumPatchSize = headerSize + 3;
		// "EOF" magic string
		static constexpr usize endOfFile = 0x454F46;

		template <typename T = u64, usize size>
		T read(const u8* data, usize& offset, usize patchSize) {
			return Detail::readBE<T, size>(data, offset, patchSize);
		}

		// The size isn't even encoded in the file properly, so we need to parse the file one time first to figure it out...
		static usize getSize(const u8* patch, usize patchSize) {
			usize outputSize = 0;
			usize patchOffset = headerSize;  // Skip header bytes

			while (patchOffset < patchSize) {
				const usize fileOffset = read<usize, 3>(patch, patchOffset, patchSize);

				if (fileOffset == endOfFile) {
					break;
				}

				usize newSize = fileOffset;
				const u16 size = read<u16, 2>(patch, patchOffset, patchSize);
				// RLE encoding
				if (size == 0) {
					const u16 rleSize = read<u16, 2>(patch, patchOffset, patchSize);
					newSize += rleSize;

					patchOffset += 1;  // Skip value field
				} else {
					patchOffset += size;  // Skip data field
					newSize += size;
				}

				outputSize = std::max<usize>(outputSize, newSize);
			}

			if (patchOffset + 3 == patchSize) {
				// Apparently some IPS files have a 3 byte footer with the ROM size after EOF
				const usize actualSize = read<usize, 3>(patch, patchOffset, patchSize);
				outputSize = std::max<usize>(outputSize, actualSize);
			}

			return outputSize;
		}
	};  // namespace IPS

	static std::pair<std::vector<u8>, Result> patchIPS(const u8* data, usize dataSize, const u8* patch, usize patchSize) {
		if (patch == nullptr || patchSize < IPS::minimumPatchSize) [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		// Header magic does not match, so the patch is invalid
		if (patch[0] != 'P' || patch[1] != 'A' || patch[2] != 'T' || patch[3] != 'C' || patch[4] != 'H') [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		// Copy file to be patched in output buffer
		std::vector<u8> output(IPS::getSize(patch, patchSize));
		std::memcpy(output.data(), data, std::min<u64>(output.size(), dataSize));

		// Skip header
		usize offset = IPS::headerSize;
		while (offset < patchSize) {
			// Read the next record, starting from the 3-byte offset where the patch will be placed in the file to patch
			const usize fileOffset = IPS::read<usize, 3>(patch, offset, patchSize);
			if (fileOffset == IPS::endOfFile) {
				// If we detect EOF, we are done applying the patch
				break;
			}

			// Size of data to copy
			u16 size = IPS::read<u16, 2>(patch, offset, patchSize);
			if (size == 0) {
				// RLE encoding
				u16 rleSize = IPS::read<u16, 2>(patch, offset, patchSize);
				u8 value = IPS::read<u8, 1>(patch, offset, patchSize);

				for (int i = 0; i < rleSize; i++) {
					// Going out of ROM bounds
					if (fileOffset + i >= output.size()) {
						break;
					}

					output[fileOffset + i] = value;
				}
			} else {
				for (int i = 0; i < size; i++) {
					// Going out of ROM bounds
					if (fileOffset + i >= output.size()) {
						break;
					}

					output[fileOffset + i] = IPS::read<u8, 1>(patch, offset, patchSize);
				}
			}
		}

		return {output, Result::Success};
	}

	namespace UPS {
		static constexpr usize headerSize = 4;
		// Need at least 4 (header) + 2 (minimum size for input/output sizes) + crc32s for input file, output file and patch
		static constexpr usize minimumPatchSize = 18;

		template <typename T = u64, usize size>
		T read(const u8* data, usize& offset, usize patchSize) {
			return Detail::readLE<T, size>(data, offset, patchSize);
		}

		template <typename T = u64>
		T readRunLength(const u8* data, usize& offset, usize patchSize) {
			return Detail::readRunLength<T>(data, offset, patchSize);
		}
	}  // namespace UPS

	static std::pair<std::vector<u8>, Result> patchUPS(const u8* data, usize dataSize, const u8* patch, usize patchSize) {
		if (patch == nullptr || patchSize < IPS::minimumPatchSize) [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		// Header magic does not match, so the patch is invalid
		if (patch[0] != 'U' || patch[1] != 'P' || patch[2] != 'S' || patch[3] != '1') [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		usize patchOffset = UPS::headerSize;
		const u64 inputSize = UPS::readRunLength<u64>(patch, patchOffset, patchSize);
		const u64 outputSize = UPS::readRunLength<u64>(patch, patchOffset, patchSize);

		// The file we're trying to patch is smaller than the input is meant to be, reject it
		if (dataSize < inputSize) {
			return {{}, Result::SizeMismatch};
		}

		std::vector<u8> output(outputSize);
		usize sourceOffset = 0;
		usize outputOffset = 0;

		while (patchOffset < patchSize - 12) {
			u64 length = UPS::readRunLength<u64>(patch, patchOffset, patchSize);

			// Copy length bytes as-is
			while (length > 0 && outputOffset < outputSize) {
				output[outputOffset++] = UPS::read<u8, 1>(data, sourceOffset, dataSize);
				length -= 1;
			}

			while (outputOffset < outputSize) {
				// Patch with XOR until we find the terminating patch value (0x00)
				// Patching with XOR means patches are reversible, by simply applying the patch again
				const u8 sourceValue = UPS::read<u8, 1>(data, sourceOffset, dataSize);
				const u8 patchValue = UPS::read<u8, 1>(patch, patchOffset, patchSize);
				output[outputOffset++] = sourceValue ^ patchValue;

				// We need to check for this after applying the xor patch, otherwise the offset values will be wrong
				if (patchValue == 0) {
					break;
				}
			}
		}

		while (outputOffset < outputSize && sourceOffset < dataSize) {
			// Copy the rest of the bytes
			output[outputOffset++] = UPS::read<u8, 1>(data, sourceOffset, dataSize);
		}

		// Pad rest of the output with 0s
		while (outputOffset < outputSize) {
			output[outputOffset++] = 0;
		}

		const u32 inputCRC = UPS::read<u32, 4>(patch, patchOffset, patchSize);
		const u32 outputCRC = UPS::read<u32, 4>(patch, patchOffset, patchSize);
		const u32 patchCRC = UPS::read<u32, 4>(patch, patchOffset, patchSize);

		if (outputCRC != Detail::crc32(output.data(), output.size())) {
			return {output, Result::ChecksumMismatch};
		}

		return {output, Result::Success};
	}

	namespace BPS {
		static constexpr usize headerSize = 4;
		// Need at least 5 (header) + 3 (source/target/metadata size) + 9 (checksums) bytes to be a valid BPS patch
		static constexpr usize minimumPatchSize = headerSize + 3 + 9;

		template <typename T = u64, usize size>
		T read(const u8* data, usize& offset, usize patchSize) {
			return Detail::readLE<T, size>(data, offset, patchSize);
		}

		template <typename T = u64>
		T readRunLength(const u8* data, usize& offset, usize patchSize) {
			return Detail::readRunLength<T>(data, offset, patchSize);
		}

		namespace Action {
			enum : u32 {
				SourceRead = 0,
				TargetRead = 1,
				SourceCopy = 2,
				TargetCopy = 3,
			};
		}
	}  // namespace BPS

	static std::pair<std::vector<u8>, Result> patchBPS(const u8* data, usize dataSize, const u8* patch, usize patchSize) {
		if (patch == nullptr || patchSize < BPS::minimumPatchSize) [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		// Header magic does not match, so the patch is invalid
		if (patch[0] != 'B' || patch[1] != 'P' || patch[2] != 'S' || patch[3] != '1') [[unlikely]] {
			return {{}, Result::InvalidPatch};
		}

		usize patchOffset = BPS::headerSize;
		const u64 inputSize = BPS::readRunLength<u64>(patch, patchOffset, patchSize);
		const u64 outputSize = BPS::readRunLength<u64>(patch, patchOffset, patchSize);
		const u64 metadataSize = BPS::readRunLength<u64>(patch, patchOffset, patchSize);

		// The file we're trying to patch is smaller than the input is meant to be, reject it
		if (dataSize < inputSize) {
			return {{}, Result::SizeMismatch};
		}

		// Copy file to be patched in output buffer
		std::vector<u8> output(outputSize);
		usize sourceOffset = 0;
		usize outputOffset = 0;
		usize outputOffset2 = 0; // Offset used for TargetCopy commands

		while (patchOffset < patchSize - 12) {
			// Each "record" in a BPS patch consists of a VLE word, whose bottom 2 bits are a patching "action" to perform
			// And the top bits are the length of memory to operate on
			const u64 word = BPS::readRunLength<u64>(patch, patchOffset, patchSize);
			const u64 action = (word & 3);
			u64 length = (word >> 2) + 1;

			switch (action) {
				case BPS::Action::SourceRead: {
					while (length > 0 && outputOffset < outputSize && outputOffset < dataSize) {
						output[outputOffset] = data[outputOffset];
						outputOffset += 1;
						length -= 1;
					}
					break;
				}

				case BPS::Action::TargetRead: {
					while (length > 0 && outputOffset < outputSize) {
						output[outputOffset++] = BPS::read<u8, 1>(patch, patchOffset, patchSize);
						length -= 1;
					}
					break;
				}

				case BPS::Action::SourceCopy: {
					const u64 word = BPS::readRunLength<u64>(patch, patchOffset, patchSize);
					const s64 offset = s64(word >> 1);
					sourceOffset += (word & 1) ? -offset : +offset;

					while (length > 0) {
						output[outputOffset++] = data[sourceOffset++];
						length -= 1;
					}
					break;
				}

				case BPS::Action::TargetCopy: {
					const u64 data = BPS::readRunLength<u64>(patch, patchOffset, patchSize);
					const s64 offset = s64(data >> 1);
					outputOffset2 += (data & 1) ? -offset : +offset;

					while (length > 0) {
						output[outputOffset++] = output[outputOffset2++];
						length -= 1;
					}
					break;
				}
			}
		}

		// Pad rest of the output with 0s
		while (outputOffset < outputSize) {
			output[outputOffset++] = 0;
		}

		const u32 inputCRC = BPS::read<u32, 4>(patch, patchOffset, patchSize);
		const u32 outputCRC = BPS::read<u32, 4>(patch, patchOffset, patchSize);
		const u32 patchCRC = BPS::read<u32, 4>(patch, patchOffset, patchSize);

		if (outputCRC != Detail::crc32(output.data(), output.size())) {
			return {output, Result::ChecksumMismatch};
		}

		return {output, Result::Success};
	}

	static std::pair<std::vector<u8>, Result> patch(const u8* data, usize dataSize, const u8* patch, usize patchSize, PatchType type) {
		switch (type) {
			case PatchType::IPS: return patchIPS(data, dataSize, patch, patchSize);
			case PatchType::UPS: return patchUPS(data, dataSize, patch, patchSize);
			case PatchType::BPS: return patchBPS(data, dataSize, patch, patchSize);
			default: return {{}, Result::UnknownFormat};  // Unknown patch format
		}
	}
}  // namespace Hips