Base58编码简析与C++实现
参照:
https://en.wikipedia.org/wiki/Base58
https://en.wikipedia.org/wiki/Binary-to-text_encoding
https://en.bitcoin.it/wiki/Base58Check_encoding
Base58可以简单理解为将数据,以58进制的形式进行表示。
实现伪代码如下:
code_string = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
x = convert_bytes_to_big_integer(hash_result)
output_string = ""
while(x > 0)
{
(x, remainder) = divide(x, 58)
output_string.append(code_string[remainder])
}
repeat(number_of_leading_zero_bytes_in_hash)
{
output_string.append(code_string[0]);
}
output_string.reverse();
大值思路为:
1. 将数据转换为大整数x,
2. 依次将(x % 58)的值表示的编码添加到输出字符串末尾;
3. 令x = ( x / 58 );
4. 重复2-3,直到x等于0;
5. 将数据前所有0的编码(即“1”)添加到输出字符串末尾;
6. 将输出字符串反转,即为Base58编码字符串。
由于编码前数据可以视为256进制编码数据,所以转换为58进制编码数据后,数据长度为变长。
假设原长度为Len256,转换为长度为Len58,则:
Len58 = Len256 * ( log256 / log58 ) + 1
Bitcoin(0.16.0)中实现代码如下:
/** All alphanumeric characters except for "0", "I", "O", and "l" */
static const char* pszBase58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
{
// Skip leading spaces.
while (*psz && isspace(*psz))
psz++;
// Skip and count leading '1's.
int zeroes = 0;
int length = 0;
while (*psz == '1') {
zeroes++;
psz++;
}
// Allocate enough space in big-endian base256 representation.
int size = strlen(psz) * 733 /1000 + 1; // log(58) / log(256), rounded up.
std::vector<unsigned char> b256(size);
// Process the characters.
while (*psz && !isspace(*psz)) {
// Decode base58 character
const char* ch = strchr(pszBase58, *psz);
if (ch == nullptr)
return false;
// Apply "b256 = b256 * 58 + ch".
int carry = ch - pszBase58;
int i = 0;
for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); ++it, ++i) {
carry += 58 * (*it);
*it = carry % 256;
carry /= 256;
}
assert(carry == 0);
length = i;
psz++;
}
// Skip trailing spaces.
while (isspace(*psz))
psz++;
if (*psz != 0)
return false;
// Skip leading zeroes in b256.
std::vector<unsigned char>::iterator it = b256.begin() + (size - length);
while (it != b256.end() && *it == 0)
it++;
// Copy result into output vector.
vch.reserve(zeroes + (b256.end() - it));
vch.assign(zeroes, 0x00);
while (it != b256.end())
vch.push_back(*(it++));
return true;
}
std::string EncodeBase58(const unsigned char* pbegin, const unsigned char* pend)
{
// Skip & count leading zeroes.
int zeroes = 0;
int length = 0;
while (pbegin != pend && *pbegin == 0) {
pbegin++;
zeroes++;
}
// Allocate enough space in big-endian base58 representation.
int size = (pend - pbegin) * 138 / 100 + 1; // log(256) / log(58), rounded up.
std::vector<unsigned char> b58(size);
// Process the bytes.
while (pbegin != pend) {
int carry = *pbegin;
int i = 0;
// Apply "b58 = b58 * 256 + ch".
for (std::vector<unsigned char>::reverse_iterator it = b58.rbegin(); (carry != 0 || i < length) && (it != b58.rend()); it++, i++) {
carry += 256 * (*it);
*it = carry % 58;
carry /= 58;
}
assert(carry == 0);
length = i;
pbegin++;
}
// Skip leading zeroes in base58 result.
std::vector<unsigned char>::iterator it = b58.begin() + (size - length);
while (it != b58.end() && *it == 0)
it++;
// Translate the result into a string.
std::string str;
str.reserve(zeroes + (b58.end() - it));
str.assign(zeroes, '1');
while (it != b58.end())
str += pszBase58[*(it++)];
return str;
}
std::string EncodeBase58(const std::vector<unsigned char>& vch)
{
return EncodeBase58(vch.data(), vch.data() + vch.size());
}
bool DecodeBase58(const std::string& str, std::vector<unsigned char>& vchRet)
{
return DecodeBase58(str.c_str(), vchRet);
}
编码与解码,即为256进制与58进制大数据间的相互转换。