base58.c

/*
 * Copyright (c) 2014 Luke Dashjr
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

static const int8_t b58digits_map[] = {
	-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, 0, 1, 2, 3, 4, 5, 6,  7, 8,-1,-1,-1,-1,-1,-1,
	-1, 9,10,11,12,13,14,15, 16,-1,17,18,19,20,21,-1,
	22,23,24,25,26,27,28,29, 30,31,32,-1,-1,-1,-1,-1,
	-1,33,34,35,36,37,38,39, 40,41,42,43,-1,44,45,46,
	47,48,49,50,51,52,53,54, 55,56,57,-1,-1,-1,-1,-1,
};

typedef uint64_t b58_maxint_t;
typedef uint32_t b58_almostmaxint_t;
#define b58_almostmaxint_bits (sizeof(b58_almostmaxint_t) * 8)
static const b58_almostmaxint_t b58_almostmaxint_mask = ((((b58_maxint_t)1) << b58_almostmaxint_bits) - 1);

bool b58tobin(unsigned char *bin, size_t *binszp, const char *b58, size_t b58sz)
{
	size_t binsz = *binszp;
	const unsigned char *b58u = (unsigned char*)b58;
	unsigned char *binu = bin;
	size_t outisz = (binsz + sizeof(b58_almostmaxint_t) - 1) / sizeof(b58_almostmaxint_t);
	b58_almostmaxint_t outi[outisz];
	b58_maxint_t t;
	b58_almostmaxint_t c;
	size_t i, j;
	uint8_t bytesleft = binsz % sizeof(b58_almostmaxint_t);
	b58_almostmaxint_t zeromask = bytesleft ? (b58_almostmaxint_mask << (bytesleft * 8)) : 0;
	unsigned zerocount = 0;
	
	if (!b58sz)
		b58sz = strlen(b58);
	
	for (i = 0; i < outisz; ++i) {
		outi[i] = 0;
	}
	
	// Leading zeros, just count
	for (i = 0; i < b58sz && b58u[i] == '1'; ++i)
		++zerocount;
	
	for ( ; i < b58sz; ++i)
	{
		if (b58u[i] & 0x80)
			// High-bit set on invalid digit
			return false;
		if (b58digits_map[b58u[i]] == -1)
			// Invalid base58 digit
			return false;
		c = (unsigned)b58digits_map[b58u[i]];
		for (j = outisz; j--; )
		{
			t = ((b58_maxint_t)outi[j]) * 58 + c;
			c = t >> b58_almostmaxint_bits;
			outi[j] = t & b58_almostmaxint_mask;
		}
		if (c)
			// Output number too big (carry to the next int32)
			return false;
		if (outi[0] & zeromask)
			// Output number too big (last int32 filled too far)
			return false;
	}
	
	j = 0;
	if (bytesleft) {
		for (i = bytesleft; i > 0; --i) {
			*(binu++) = (outi[0] >> (8 * (i - 1))) & 0xff;
		}
		++j;
	}
	
	for (; j < outisz; ++j)
	{
		for (i = sizeof(*outi); i > 0; --i) {
			*(binu++) = (outi[j] >> (8 * (i - 1))) & 0xff;
		}
	}
	
	// Count canonical base58 byte count
	binu = bin;
	for (i = 0; i < binsz; ++i)
	{
		if (binu[i])
			break;
		--*binszp;
	}
	*binszp += zerocount;
	
	return true;
}

static const char b58digits_ordered[] = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";

bool b58enc(char *b58, size_t *b58sz, const unsigned char *data, size_t binsz)
{
	const uint8_t *bin = data;
	int carry;
	size_t i, j, high, zcount = 0;
	size_t size;
	
	while (zcount < binsz && !bin[zcount])
		++zcount;
	
	size = (binsz - zcount) * 138 / 100 + 1;
	uint8_t buf[size];
	memset(buf, 0, size);
	
	for (i = zcount, high = size - 1; i < binsz; ++i, high = j)
	{
		for (carry = bin[i], j = size - 1; (j > high) || carry; --j)
		{
			carry += 256 * buf[j];
			buf[j] = carry % 58;
			carry /= 58;
			if (!j) {
				// Otherwise j wraps to maxint which is > high
				break;
			}
		}
	}
	
	for (j = 0; j < size && !buf[j]; ++j);
	
	if (*b58sz <= zcount + size - j)
	{
		*b58sz = zcount + size - j + 1;
		return false;
	}
	
	if (zcount)
		memset(b58, '1', zcount);
	for (i = zcount; j < size; ++i, ++j)
		b58[i] = b58digits_ordered[buf[j]];
	b58[i] = '\0';
	*b58sz = i + 1;
	
	return true;
}