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db_block.cpp: Fix tapos rollover logic

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theoreticalbts 2015-06-30 17:02:21 -04:00
parent f46758e97c
commit 5f5e761ca8
1 changed files with 55 additions and 3 deletions
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58
libraries/chain/db_block.cpp
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@ -468,10 +468,62 @@ processed_transaction database::_apply_transaction( const signed_transaction& tr
//Check the TaPoS reference and expiration time
//Remember that the TaPoS block number is abbreviated; it contains only the lower 16 bits.
//Lookup TaPoS block summary by block number (remember block summary instances are the block numbers)
// Let N = head_block_num(), a = N & 0xFFFF, and r = trx.ref_block_num
//
// We want to solve for the largest block height x such that
// these two conditions hold:
//
// (a) 0x10000 divides x-r
// (b) x <= N
//
// Let us define:
//
// x1 = N-a+r
// x0 = x1-2^16
// x2 = x1+2^16
//
// It is clear that x0, x1, x2 are consecutive solutions to (a).
//
// Since r < 2^16 and a < 2^16, it follows that
// -2^16 < r-a < 2^16. From this we know that x0 < N and x2 > N.
//
// Case (1): x1 <= N. In this case, x1 must be the greatest
// integer that satisfies (a) and (b); for x2, the next
// largest integer that satisfies (a), does not satisfy (b).
//
// Case (2): x1 > N. In this case, x0 must be the greatest
// integer that satisfies (a) and (b); for x1, the next
// largest integer that satisfies (a), does not satisfy (b).
//
int64_t N = head_block_num();
int64_t a = N & 0xFFFF;
int64_t r = trx.ref_block_num;
int64_t x1 = N-a+r;
int64_t x0 = x1 - 0x10000;
int64_t x2 = x1 + 0x10000;
assert( x0 < N );
assert( x1 >= 0 );
assert( x2 > N );
uint32_t ref_block_height;
if( x1 <= N )
{
FC_ASSERT( x1 > 0 );
ref_block_height = uint32_t( x1 );
}
else
{
ref_block_height = uint32_t( x0 );
}
const block_summary_object& tapos_block_summary
= static_cast<const block_summary_object&>(get_index<block_summary_object>()
.get(block_summary_id_type((head_block_num() & ~0xffff)
+ trx.ref_block_num)));
= static_cast<const block_summary_object&>(
get_index<block_summary_object>()
.get(block_summary_id_type(ref_block_height))
);
//This is the signature check for transactions with relative expiration.
if( !(skip & skip_transaction_signatures) )