text: // Copyright (c) 2014-2017, The X12 Project
  // 
  // All rights reserved.
  // 
  // Redistribution and use in source and binary forms, with or without modification, are
  // permitted provided that the following conditions are met:
  // 
  // 1. Redistributions of source code must retain the above copyright notice, this list of
  //    conditions and the following disclaimer.
  // 
  // 2. Redistributions in binary form must reproduce the above copyright notice, this list
  //    of conditions and the following disclaimer in the documentation and/or other
  //    materials provided with the distribution.
  // 
  // 3. Neither the name of the copyright holder nor the names of its contributors may be
  //    used to endorse or promote products derived from this software without specific
  //    prior written permission.
  // 
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  // EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
  // THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  // 
  // Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers
  
  #include <assert.h>
  #include <stddef.h>
  #include <string.h>
  
  #include "hash-ops.h"
  
  #if !defined(__FreeBSD__) && !defined(__OpenBSD__) && !defined(__DragonFly__)
   #include <alloca.h>
  #else
   #include <stdlib.h>
  #endif
  
  /*** 
  * Round to power of two, for count>=3 and for count being not too large (as reasonable for tree hash calculations)
  */
  size_t tree_hash_cnt(size_t count) {
  	// This algo has some bad history but all we are doing is 1 << floor(log2(count))
  	// There are _many_ ways to do log2, for some reason the one selected was the most obscure one,
  	// and fixing it made it even more obscure.
  	//
  	// Iterative method implemented below aims for clarity over speed, if performance is needed
  	// then my advice is to use the BSR instruction on x86
  	//
  	// All the paranoid asserts have been removed since it is trivial to mathematically prove that
  	// the return will always be a power of 2.
  	// Problem space has been defined as 3 <= count <= 2^28. Of course quarter of a billion transactions
  	// is not a sane upper limit for a block, so there will be tighter limits in other parts of the code
  
  	assert( count >= 3 ); // cases for 0,1,2 are handled elsewhere
  	assert( count <= 0x10000000 ); // sanity limit to 2^28, MSB=1 will cause an inf loop
  
  	size_t pow = 2;
  	while(pow < count) pow <<= 1;
  	return pow >> 1;
  }
  
  void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) {
  // The blockchain block at height 202612 http://x12coin.com/block/bbd604d2ba11ba27935e006ed39c9bfdd99b76bf4a50654bc1e1e61217962698
  // contained 514 transactions, that triggered bad calculation of variable "cnt" in the original version of this function
  // as from CryptoNote code.
  //
  // This bug applies to all CN altcoins.
  //
  // Mathematical bug here was first published on 14:45:34 (GMT+2) 2014-09-04 by Rafal Freeman <rfree>
  // and soon also applied to CryptoNote (15:10 GMT+2), and BoolBerry used not fully correct work around:
  // the work around of sizeof(size_t)*8 or <<3 as used before in 2 coins and in BBL later was blocking
  // exploitation on normal platforms, how ever we strongly recommend the following fix because it removes
  // mistake in mathematical formula.
  
    assert(count > 0);
    if (count == 1) {
      memcpy(root_hash, hashes, HASH_SIZE);
    } else if (count == 2) {
      cn_fast_hash(hashes, 2 * HASH_SIZE, root_hash);
    } else {
      size_t i, j;
  
      size_t cnt = tree_hash_cnt( count );
  
      char (*ints)[HASH_SIZE];
      size_t ints_size = cnt * HASH_SIZE;
      ints = alloca(ints_size); 	memset( ints , 0 , ints_size);  // allocate, and zero out as extra protection for using uninitialized mem
  
      memcpy(ints, hashes, (2 * cnt - count) * HASH_SIZE);
  
      for (i = 2 * cnt - count, j = 2 * cnt - count; j < cnt; i += 2, ++j) {
        cn_fast_hash(hashes[i], 64, ints[j]);
      }
      assert(i == count);
  
      while (cnt > 2) {
        cnt >>= 1;
        for (i = 0, j = 0; j < cnt; i += 2, ++j) {
          cn_fast_hash(ints[i], 64, ints[j]);
        }
      }
  
      cn_fast_hash(ints[0], 64, root_hash);
    }
  }
  