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| author | Wladimir J. van der Laan <laanwj@gmail.com> | 2012-09-27 22:48:27 -0700 |
|---|---|---|
| committer | Wladimir J. van der Laan <laanwj@gmail.com> | 2012-09-27 22:48:27 -0700 |
| commit | 035cb4781d9463eb6db2574b18452c02c370c9a5 (patch) | |
| tree | f5761d21124dd208974f5750e1ea309977d8f209 | |
| parent | 14ac0adcc7c0224a467e38bbd4ebf39d824ada8d (diff) | |
| parent | 95d7f002957a7bb30a2d5d8b07fe8fe3c1f37ec0 (diff) | |
| download | bitcoin-035cb4781d9463eb6db2574b18452c02c370c9a5.tar.xz | |
Merge pull request #1868 from maaku/and_or_xor_sign_extension
Documented bug in sign-extension behavior of opcodes OP_AND, OP_OR, and OP_XOR
| -rw-r--r-- | src/script.cpp | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/src/script.cpp b/src/script.cpp index c34fbec82d..4357a9a1b3 100644 --- a/src/script.cpp +++ b/src/script.cpp @@ -54,12 +54,29 @@ bool CastToBool(const valtype& vch) return false; } +// +// WARNING: This does not work as expected for signed integers; the sign-bit +// is left in place as the integer is zero-extended. The correct behavior +// would be to move the most significant bit of the last byte during the +// resize process. MakeSameSize() is currently only used by the disabled +// opcodes OP_AND, OP_OR, and OP_XOR. +// void MakeSameSize(valtype& vch1, valtype& vch2) { // Lengthen the shorter one if (vch1.size() < vch2.size()) + // PATCH: + // +unsigned char msb = vch1[vch1.size()-1]; + // +vch1[vch1.size()-1] &= 0x7f; + // vch1.resize(vch2.size(), 0); + // +vch1[vch1.size()-1] = msb; vch1.resize(vch2.size(), 0); if (vch2.size() < vch1.size()) + // PATCH: + // +unsigned char msb = vch2[vch2.size()-1]; + // +vch2[vch2.size()-1] &= 0x7f; + // vch2.resize(vch1.size(), 0); + // +vch2[vch2.size()-1] = msb; vch2.resize(vch1.size(), 0); } @@ -663,6 +680,11 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co } break; + // + // WARNING: These disabled opcodes exhibit unexpected behavior + // when used on signed integers due to a bug in MakeSameSize() + // [see definition of MakeSameSize() above]. + // case OP_AND: case OP_OR: case OP_XOR: @@ -672,7 +694,7 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co return false; valtype& vch1 = stacktop(-2); valtype& vch2 = stacktop(-1); - MakeSameSize(vch1, vch2); + MakeSameSize(vch1, vch2); // <-- NOT SAFE FOR SIGNED VALUES if (opcode == OP_AND) { for (unsigned int i = 0; i < vch1.size(); i++) |