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Testnet transaction c474c67cabc13f74c65e7cf503db971d5ba176794bff7de36f46d51ca675cf3a locked 0.0005BTC with a simple math script:
OP_2DUP OP_ADD 5102 OP_EQUALVERIFY OP_SUB 230d OP_EQUAL
Transaction b6714e05dd014cc92de09271886e62d85e7d41dd44fad417c520eb51d57f94c0 spent that output with the sigscript:
ba07 6985
I can't see how (ba07 + 6985) == 5102 or (ba07 - 6985) == 230d.
What am I missing about Bitcoin script, integers, and math?
For mathematical operations, Bitcoin treats byte vectors as signed (signed magnitude) little endian values. So let's look what the numbers are then:
- The byte vector
ba07is the hexadecimal number (0)7ba. - The byte vector
6985is8569in big endian. Since the highest bit is set the number is negative. So the hexadecimal number is -(0)569. - The byte vector
5102is the hexadecimal number (0)251. - The byte vector
0d23is the hexadecimal number (0)23d.
Therefore we end up with the two statements 7ba+(-569)=251 and 7ba-(-569)=d23 which are true.
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