Fixed bug in sample_measure_using_probabilities #1132
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…asure_with_probabilities
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Fixes a bug in CopyIn/CopyOut operations where out of bounds array elemets were accessed. Qubitvector thrust has a number of qubits num_qubits. When move_to_vector or copy_to_vector functions are called a temporary array or vector of size (1 << num_qubits) is created and passed to chunk_ CopyOut function. There, a number of elements (1 << chunk_qubits_) of the underlying structure are copied to this array/vector. The problem is that chunk_qubits can be larger that num_qubits, accessing values in the array or vector out of bounds. This is what was making PR Qiskit#1132 failing in CI.
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Fixes a bug in CopyIn/CopyOut operations where out of bounds array elemets were accessed. Qubitvector thrust has a number of qubits num_qubits. When move_to_vector or copy_to_vector functions are called a temporary array or vector of size (1 << num_qubits) is created and passed to chunk_ CopyOut function. There, a number of elements (1 << chunk_qubits_) of the underlying structure are copied to this array/vector. The problem is that chunk_qubits can be larger that num_qubits, accessing values in the array or vector out of bounds. This is what was making PR #1132 failing in CI.
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Co-authored-by: Victor Villar <vvilpas@gmail.com> Co-authored-by: Christopher J. Wood <cjwood@us.ibm.com> (cherry picked from commit 7267429)
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Summary
Fixed bug reported in issue #1126
Details and comments
When measuring on a subset of the qubits, when converting the sampled measurement to register form, the result was widened to all qubits in the call to int2reg. The gives incorrect results in the final register. Instead, we should only widen to the number of measured qubits.
Closes #1126 #1165