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| author | Pavel Pisa <pisa@cmp.felk.cvut.cz> | 2019-01-31 09:44:11 +0100 |
|---|---|---|
| committer | Pavel Pisa <pisa@cmp.felk.cvut.cz> | 2019-01-31 09:44:11 +0100 |
| commit | 6a6bd48da1f09be7dc7c53f13393b07889eea364 (patch) | |
| tree | 4d00b004c93ff4952b40efcb0ddb0af3660e0685 /qtmips_machine/alu.cpp | |
| parent | 644d250ff08bbc7342b570c8684a3a15019df33c (diff) | |
| download | qtmips-6a6bd48da1f09be7dc7c53f13393b07889eea364.tar.gz qtmips-6a6bd48da1f09be7dc7c53f13393b07889eea364.tar.bz2 qtmips-6a6bd48da1f09be7dc7c53f13393b07889eea364.zip | |
Correct signed arithmetic overflow exception.
Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Diffstat (limited to 'qtmips_machine/alu.cpp')
| -rw-r--r-- | qtmips_machine/alu.cpp | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/qtmips_machine/alu.cpp b/qtmips_machine/alu.cpp index 3822955..2e36d4c 100644 --- a/qtmips_machine/alu.cpp +++ b/qtmips_machine/alu.cpp @@ -41,13 +41,17 @@ std::uint32_t machine::alu_operate(enum AluOp operation, std::uint32_t s, std::u regs->write_hi_lo(false, s); return 0x0; case ALU_OP_ADD: - if (s > (0xFFFFFFFF - t)) + /* s(31) ^ ~t(31) ... same signs on input */ + /* (s + t)(31) ^ s(31) ... different sign on output */ + if (((s ^ ~t) & ((s + t) ^ s)) & 0x80000000) throw QTMIPS_EXCEPTION(Overflow, "ADD operation overflow/underflow", QString::number(s) + QString(" + ") + QString::number(t)); FALLTROUGH case ALU_OP_ADDU: return s + t; case ALU_OP_SUB: - if (s < t) + /* s(31) ^ t(31) ... differnt signd on input */ + /* (s - t)(31) ^ ~s(31) <> 0 ... otput sign differs from s */ + if (((s ^ t) & ((s - t) ^ s)) & 0x80000000) throw QTMIPS_EXCEPTION(Overflow, "SUB operation overflow/underflow", QString::number(s) + QString(" - ") + QString::number(t)); FALLTROUGH case ALU_OP_SUBU: |