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◆ main openmsx / src / utils / Base64.cc
4.5 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
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#include "Base64.hh"
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#include "narrow.hh"
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#include "ranges.hh"
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#include "xrange.hh"
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#include <algorithm>
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#include <array>
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#include <cassert>
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namespace Base64 {
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using openmsx::MemBuffer;
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[[nodiscard]] static constexpr char encode(uint8_t c)
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{
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	constexpr std::array<char, 64> base64_chars = {
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		'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
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		'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
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		'0','1','2','3','4','5','6','7','8','9','+','/',
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	};
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	assert(c < 64);
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	return base64_chars[c];
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}
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[[nodiscard]] static constexpr uint8_t decode(uint8_t c)
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{
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	if        ('A' <= c && c <= 'Z') {
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		return c - 'A';
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	} else if ('a' <= c && c <= 'z') {
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		return c - 'a' + 26;
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	} else if ('0' <= c && c <= '9') {
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		return c - '0' + 52;
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	} else if (c == '+') {
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		return 62;
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	} else if (c == '/') {
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		return 63;
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	} else {
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		return uint8_t(-1);
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	}
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}
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std::string encode(std::span<const uint8_t> input)
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{
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	constexpr int CHUNKS = 19;
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	constexpr int IN_CHUNKS  = 3 * CHUNKS;
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	constexpr int OUT_CHUNKS = 4 * CHUNKS; // 76 chars per line
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	auto outSize = ((input.size() + (IN_CHUNKS - 1)) / IN_CHUNKS) * (OUT_CHUNKS + 1); // overestimation
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	std::string ret;
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	ret.resize_and_overwrite(outSize, [&](char* buf, size_t) {
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		size_t out = 0;
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		while (!input.empty()) {
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			if (out) buf[out++] = '\n';
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			auto n = std::min<size_t>(IN_CHUNKS, input.size());
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			for (/**/; n >= 3; n -= 3) {
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				buf[out++] = encode(uint8_t( (input[0] & 0xfc) >> 2));
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				buf[out++] = encode(uint8_t(((input[0] & 0x03) << 4) +
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							((input[1] & 0xf0) >> 4)));
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				buf[out++] = encode(uint8_t(((input[1] & 0x0f) << 2) +
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							((input[2] & 0xc0) >> 6)));
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				buf[out++] = encode(uint8_t( (input[2] & 0x3f) >> 0));
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				input = input.subspan(3);
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			}
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			if (n) {
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				std::array<uint8_t, 3> buf3 = {0, 0, 0};
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				copy_to_range(input.subspan(0, n), buf3);
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				input = input.subspan(n);
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				std::array<uint8_t, 4> buf4;
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				buf4[0] = uint8_t( (buf3[0] & 0xfc) >> 2);
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				buf4[1] = uint8_t(((buf3[0] & 0x03) << 4) +
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						((buf3[1] & 0xf0) >> 4));
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				buf4[2] = uint8_t(((buf3[1] & 0x0f) << 2) +
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						((buf3[2] & 0xc0) >> 6));
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				buf4[3] = uint8_t( (buf3[2] & 0x3f) >> 0);
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				for (auto j : xrange(n + 1)) {
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					buf[out++] = encode(buf4[j]);
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				}
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				for (/**/; n < 3; ++n) {
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					buf[out++] = '=';
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				}
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			}
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		}
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		assert(outSize >= out);
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		return out; // shrink to correct size
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	});
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	return ret;
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}
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MemBuffer<uint8_t> decode(std::string_view input)
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{
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	auto outSize = (input.size() * 3 + 3) / 4; // overestimation
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	MemBuffer<uint8_t> ret(outSize); // too big
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	unsigned i = 0;
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	size_t out = 0;
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	std::array<uint8_t, 4> buf4;
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	for (auto c : input) {
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		uint8_t d = decode(c);
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		if (d == uint8_t(-1)) continue;
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		buf4[i++] = d;
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		if (i == 4) {
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			i = 0;
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			ret[out++] = char(((buf4[0] & 0xff) << 2) + ((buf4[1] & 0x30) >> 4));
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			ret[out++] = char(((buf4[1] & 0x0f) << 4) + ((buf4[2] & 0x3c) >> 2));
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			ret[out++] = char(((buf4[2] & 0x03) << 6) + ((buf4[3] & 0xff) >> 0));
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		}
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	}
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	if (i) {
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		for (auto j : xrange(i, 4u)) {
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			buf4[j] = 0;
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		}
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		std::array<uint8_t, 3> buf3;
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		buf3[0] = narrow_cast<uint8_t>(((buf4[0] & 0xff) << 2) + ((buf4[1] & 0x30) >> 4));
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		buf3[1] = narrow_cast<uint8_t>(((buf4[1] & 0x0f) << 4) + ((buf4[2] & 0x3c) >> 2));
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		buf3[2] = narrow_cast<uint8_t>(((buf4[2] & 0x03) << 6) + ((buf4[3] & 0xff) >> 0));
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		for (auto j : xrange(i - 1)) {
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			ret[out++] = buf3[j];
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		}
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	}
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	assert(outSize >= out);
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	ret.resize(out); // shrink to correct size
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	return ret;
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}
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bool decode_inplace(std::string_view input, std::span<uint8_t> output)
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{
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	auto outSize = output.size();
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	unsigned i = 0;
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	size_t out = 0;
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	std::array<uint8_t, 4> buf4;
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	for (auto c : input) {
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		uint8_t d = decode(c);
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		if (d == uint8_t(-1)) continue;
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		buf4[i++] = d;
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		if (i == 4) {
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			i = 0;
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			if ((out + 3) > outSize) [[unlikely]] return false;
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			output[out++] = char(((buf4[0] & 0xff) << 2) + ((buf4[1] & 0x30) >> 4));
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			output[out++] = char(((buf4[1] & 0x0f) << 4) + ((buf4[2] & 0x3c) >> 2));
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			output[out++] = char(((buf4[2] & 0x03) << 6) + ((buf4[3] & 0xff) >> 0));
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		}
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	}
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	if (i) {
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		for (auto j : xrange(i, 4u)) {
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			buf4[j] = 0;
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		}
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		std::array<uint8_t, 3> buf3;
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		buf3[0] = narrow_cast<uint8_t>(((buf4[0] & 0xff) << 2) + ((buf4[1] & 0x30) >> 4));
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		buf3[1] = narrow_cast<uint8_t>(((buf4[1] & 0x0f) << 4) + ((buf4[2] & 0x3c) >> 2));
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		buf3[2] = narrow_cast<uint8_t>(((buf4[2] & 0x03) << 6) + ((buf4[3] & 0xff) >> 0));
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		for (auto j : xrange(i - 1)) {
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			if (out == outSize) [[unlikely]] return false;
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			output[out++] = buf3[j];
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		}
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	}
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	return out == outSize;
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}
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} // namespace Base64