114 lines
3.6 KiB
C++
114 lines
3.6 KiB
C++
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#include "mybase64.hpp"
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#include <climits>
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#include <cstdint>
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#include <string_view>
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namespace mybase64
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{
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static_assert(CHAR_BIT == 8);
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auto encode(std::string_view const input, char* output) -> void
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{
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static char const* const alphabet =
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"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
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"abcdefghijklmnopqrstuvwxyz"
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"0123456789+/";
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auto cursor = std::begin(input);
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auto const end = std::end(input);
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while (end - cursor >= 3)
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{
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uint32_t buffer = uint8_t(*cursor++);
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buffer <<= 8; buffer |= uint8_t(*cursor++);
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buffer <<= 8; buffer |= uint8_t(*cursor++);
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*output++ = alphabet[(buffer >> 6 * 3) % 64];
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*output++ = alphabet[(buffer >> 6 * 2) % 64];
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*output++ = alphabet[(buffer >> 6 * 1) % 64];
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*output++ = alphabet[(buffer >> 6 * 0) % 64];
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}
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if (cursor < end)
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{
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uint32_t buffer = uint8_t(*cursor++) << 10;
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if (cursor < end) buffer |= uint8_t(*cursor) << 2;
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*output++ = alphabet[(buffer >> 12) % 64];
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*output++ = alphabet[(buffer >> 6) % 64];
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*output++ = cursor < end ? alphabet[(buffer % 64)] : '=';
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*output++ = '=';
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}
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*output = '\0';
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}
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auto decode(std::string_view const input, char* const output, std::size_t* const outlen) -> bool
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{
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static int8_t const alphabet_values[] = {
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, 0x3e, -1, -1, -1, 0x3f,
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0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
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0x3c, 0x3d, -1, -1, -1, -1, -1, -1,
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-1, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
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0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
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0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
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0x17, 0x18, 0x19, -1, -1, -1, -1, -1,
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-1, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
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0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
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0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
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0x31, 0x32, 0x33, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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-1, -1, -1, -1, -1, -1, -1, -1,
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};
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uint32_t buffer = 1;
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char* cursor = output;
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for (char c : input) {
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int8_t const value = alphabet_values[uint8_t(c)];
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if (-1 == value) continue;
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buffer = (buffer << 6) | value;
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if (buffer & 1<<6*4) {
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*cursor++ = buffer >> 8*2;
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*cursor++ = buffer >> 8*1;
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*cursor++ = buffer >> 8*0;
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buffer = 1;
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}
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}
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if (buffer & 1<<6*3) {
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*cursor++ = buffer >> 10;
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*cursor++ = buffer >> 2;
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} else if (buffer & 1<<6*2) {
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*cursor++ = buffer >> 4;
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} else if (buffer & 1<<6*1) {
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return false;
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}
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*outlen = cursor - output;
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return true;
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}
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} // namespace
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