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This commit is contained in:
Eric Mertens
2025-01-22 20:33:17 -08:00
parent efb49b8708
commit d11412e73f
13 changed files with 334 additions and 16 deletions
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2
mybase64/CMakeLists.txt Normal file
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add_library(mybase64 STATIC mybase64.cpp)
target_include_directories(mybase64 PUBLIC include)

44
mybase64/include/mybase64.hpp Normal file
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/**
* @file mybase64.hpp
* @author Eric Mertens (emertens@gmail.com)
* @brief Base64 encoding and decoding
*
*/
#pragma once
#include <cstddef>
#include <string_view>
namespace mybase64
{
inline constexpr auto encoded_size(std::size_t len) -> std::size_t
{
return (len + 2) / 3 * 4;
}
inline constexpr auto decoded_size(std::size_t len) -> std::size_t
{
return (len + 3) / 4 * 3;
}
/**
* @brief Encode a string into base64
*
* @param input input text
* @param output Target buffer for encoded value
*/
auto encode(std::string_view input, char* output) -> void;
/**
* @brief Decode a base64 encoded string
*
* @param input Base64 input text
* @param output Target buffer for decoded value
* @param outlen Output parameter for decoded length
* @return true success
* @return false failure
*/
auto decode(std::string_view input, char* output, std::size_t* outlen) -> bool;
} // namespace

113
mybase64/mybase64.cpp Normal file
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#include "mybase64.hpp"
#include <climits>
#include <cstdint>
#include <string_view>
namespace mybase64
{
static_assert(CHAR_BIT == 8);
auto encode(std::string_view const input, char* output) -> void
{
static char const* const alphabet =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";
auto cursor = std::begin(input);
auto const end = std::end(input);
while (end - cursor >= 3)
{
uint32_t buffer = uint8_t(*cursor++);
buffer <<= 8; buffer |= uint8_t(*cursor++);
buffer <<= 8; buffer |= uint8_t(*cursor++);
*output++ = alphabet[(buffer >> 6 * 3) % 64];
*output++ = alphabet[(buffer >> 6 * 2) % 64];
*output++ = alphabet[(buffer >> 6 * 1) % 64];
*output++ = alphabet[(buffer >> 6 * 0) % 64];
}
if (cursor < end)
{
uint32_t buffer = uint8_t(*cursor++) << 10;
if (cursor < end) buffer |= uint8_t(*cursor) << 2;
*output++ = alphabet[(buffer >> 12) % 64];
*output++ = alphabet[(buffer >> 6) % 64];
*output++ = cursor < end ? alphabet[(buffer % 64)] : '=';
*output++ = '=';
}
*output = '\0';
}
auto decode(std::string_view const input, char* const output, std::size_t* const outlen) -> bool
{
static int8_t const alphabet_values[] = {
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, 0x3e, -1, -1, -1, 0x3f,
0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
0x3c, 0x3d, -1, -1, -1, -1, -1, -1,
-1, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
0x17, 0x18, 0x19, -1, -1, -1, -1, -1,
-1, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
0x31, 0x32, 0x33, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
};
uint32_t buffer = 1;
char* cursor = output;
for (char c : input) {
int8_t const value = alphabet_values[uint8_t(c)];
if (-1 == value) continue;
buffer = (buffer << 6) | value;
if (buffer & 1<<6*4) {
*cursor++ = buffer >> 8*2;
*cursor++ = buffer >> 8*1;
*cursor++ = buffer >> 8*0;
buffer = 1;
}
}
if (buffer & 1<<6*3) {
*cursor++ = buffer >> 10;
*cursor++ = buffer >> 2;
} else if (buffer & 1<<6*2) {
*cursor++ = buffer >> 4;
} else if (buffer & 1<<6*1) {
return false;
}
*outlen = cursor - output;
return true;
}
} // namespace