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vm: fix MODPOW operation #3649

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merged 1 commit into from
Oct 31, 2024
+12 −4
Merged

vm: fix MODPOW operation #3649

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4 changes: 2 additions & 2 deletions pkg/compiler/syscall_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -375,9 +375,9 @@ func TestOpcode(t *testing.T) {
}`
eval(t, src, []stackitem.Item{
stackitem.Make(1),
stackitem.Make(2),
stackitem.Make(-3),
stackitem.Make(1),
stackitem.Make(2),
stackitem.Make(-3),
stackitem.Make(52),
})
})
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6 changes: 6 additions & 0 deletions pkg/vm/vm.go
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Expand Up @@ -1055,6 +1055,12 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
panic("zero modulus") // https://docs.microsoft.com/en-us/dotnet/api/system.numerics.biginteger.modpow?view=net-6.0#exceptions
}
res.Exp(base, exponent, modulus)

// https://github.com/nspcc-dev/neo-go/issues/3612
if base.Sign() < 0 && exponent.Bit(0) == 1 && res.Sign() != 0 {
absModulus := new(big.Int).Abs(modulus)
res.Sub(res, absModulus)
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}
}

v.estack.PushItem(stackitem.NewBigInteger(res))
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6 changes: 4 additions & 2 deletions pkg/vm/vm_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -747,11 +747,12 @@ func TestMODMUL(t *testing.T) {
func TestMODPOW(t *testing.T) {
prog := makeProgram(opcode.MODPOW)
t.Run("good, positive base", getTestFuncForVM(prog, 1, 3, 4, 5))
t.Run("good, negative base", getTestFuncForVM(prog, 2, -3, 5, 5))
t.Run("good, negative base", getTestFuncForVM(prog, -3, -3, 5, 5))
t.Run("good, positive base, negative mod", getTestFuncForVM(prog, 1, 3, 4, -5))
t.Run("good, negative base, negative mod", getTestFuncForVM(prog, 2, -3, 5, -5))
t.Run("good, negative base, negative mod", getTestFuncForVM(prog, -3, -3, 5, -5))
t.Run("bad, big negative exponent", getTestFuncForVM(prog, nil, 3, -2, 5))
t.Run("bad, zero modulus", getTestFuncForVM(prog, nil, 3, 4, 0))
t.Run("zero result, negative base, even exponent", getTestFuncForVM(prog, 0, -2, 3, 8))

t.Run("inverse compatibility", func(t *testing.T) { // Tests are taken from C# node.
t.Run("bad mod", getTestFuncForVM(prog, nil, 1, -1, 0))
Expand All @@ -760,6 +761,7 @@ func TestMODPOW(t *testing.T) {
t.Run("bad base", getTestFuncForVM(prog, nil, 0, -1, 1))
t.Run("no inverse exists", getTestFuncForVM(prog, nil, math.MaxUint16, -1, math.MaxUint8))
t.Run("good", getTestFuncForVM(prog, 52, 19, -1, 141))
t.Run("good", getTestFuncForVM(prog, 1, 5, -1, 4))
})
}

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