Re: DNotes 2.0 - Bridging the Gap Between the Centralized and Decentralized World

Found the issue -- it's a floating point bug in GetBlockValue()

Thanks flound1129! That is correct, some blocks like 2103797 reward 20.36265624 rather than (25*math.pow(0.95,4)) 20.36265625. The mystery remains, why your node rejects it and all the others seem fine with it.

It's not really a mystery, pow(0.95,4)*25 at https://github.com/DNotesCoin/DNotes/blob/master/src/main.cpp#L851-L853 evaluates to 20.362656249999997 on my system, which evaluates to False in the comparison at https://github.com/DNotesCoin/DNotes/blob/master/src/main.cpp#L1431 when the coinbase transaction vtx[0].getValueOut() == 20.36265625 and thus the block is considered invalid.

Minor correction, since nSubsidy starts out as an int64, the math should be pow(0.95,4)*2500000000 == 2036265624.9999998, which is being cast back to an int64 type at https://github.com/DNotesCoin/DNotes/blob/master/src/main.cpp#L853

Expected behavior when casting a floating point value to an int is that the number is truncated (not rounded). See https://stackoverflow.com/questions/9695329/c-how-to-round-a-double-to-an-int

Patching main.cpp in the following manner (assuming rounding is the desired behavior) appears to fix the issue:

Code:

diff --git a/src/main.cpp b/src/main.cpp
index 4773964..48d7b3c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -850,7 +850,7 @@ int64 static GetBlockValue(int nHeight, int64 nFees)
   {
   int yearsElapsed = nHeight / 525949;
   double nReductionPercentage = pow(0.95,yearsElapsed);
- nSubsidy = nSubsidy * nReductionPercentage;
+ nSubsidy = (int64) ((nSubsidy * nReductionPercentage)+0.5);
   }
   return nSubsidy + nFees;
}