text: /*
   * Copyright 2012-2014 Luke Dashjr
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the standard MIT license.  See COPYING for more details.
   */
  
  #include <stdbool.h>
  #include <stddef.h>
  #include <stdint.h>
  #include <string.h>
  
  #include "libbase58.h"
  
  bool (*b58_sha256_impl)(void *, const void *, size_t) = NULL;
  
  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(void *bin, size_t *binszp, const char *b58, size_t b58sz)
  {
  	size_t binsz = *binszp;
  	const unsigned char *b58u = (void*)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
  bool my_dblsha256(void *hash, const void *data, size_t datasz)
  {
  	uint8_t buf[0x20];
  	return b58_sha256_impl(buf, data, datasz) && b58_sha256_impl(hash, buf, sizeof(buf));
  }
  
  int b58check(const void *bin, size_t binsz, const char *base58str, size_t b58sz)
  {
  	unsigned char buf[32];
  	const uint8_t *binc = bin;
  	unsigned i;
  	if (binsz < 4)
  		return -4;
  	if (!my_dblsha256(buf, bin, binsz - 4))
  		return -2;
  	if (memcmp(&binc[binsz - 4], buf, 4))
  		return -1;
  	
  	// Check number of zeros is correct AFTER verifying checksum (to avoid possibility of accessing base58str beyond the end)
  	for (i = 0; binc[i] == '\0' && base58str[i] == '1'; ++i)
  	{}  // Just finding the end of zeros, nothing to do in loop
  	if (binc[i] == '\0' || base58str[i] == '1')
  		return -3;
  	
  	return binc[0];
  }
  
  static const char b58digits_ordered[] = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
  
  bool b58enc(char *b58, size_t *b58sz, const void *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;
  }
  
  bool b58check_enc(char *b58c, size_t *b58c_sz, uint8_t ver, const void *data, size_t datasz)
  {
  	uint8_t buf[1 + datasz + 0x20];
  	uint8_t *hash = &buf[1 + datasz];
  	
  	buf[0] = ver;
  	memcpy(&buf[1], data, datasz);
  	if (!my_dblsha256(hash, buf, datasz + 1))
  	{
  		*b58c_sz = 0;
  		return false;
  	}
  	
  	return b58enc(b58c, b58c_sz, buf, 1 + datasz + 4);
  }
  