separated pauli logic from paulis.cpp

since paulis.cpp is an "API" file while the pauli logic previously therein was used by numerous core files.

A final inelegance remains; some unit test utilities leverage the internal pauli logic functions using extern, which will break when we eventually switch to private namespacing. Alas!

Author: TysonRayJones

quest/src/api/matrices.cpp

@@ -16,6 +16,7 @@
 #include "quest/src/core/autodeployer.hpp"
 #include "quest/src/core/utilities.hpp"
 #include "quest/src/core/localiser.hpp"
+#include "quest/src/core/paulilogic.hpp"
 #include "quest/src/core/printer.hpp"
 #include "quest/src/core/bitwise.hpp"
 #include "quest/src/core/fastmath.hpp"
@@ -629,9 +630,6 @@ extern "C" {
  */
 
 
-extern int paulis_getIndOfLefmostNonIdentityPauli(PauliStrSum sum);
-
-
 extern "C" void setFullStateDiagMatrFromPauliStrSum(FullStateDiagMatr out, PauliStrSum in) {
     validate_matrixFields(out, __func__);
     validate_pauliStrSumFields(in, __func__);

quest/src/api/multiplication.cpp

@@ -14,6 +14,7 @@
 #include "quest/src/core/validation.hpp"
 #include "quest/src/core/utilities.hpp"
 #include "quest/src/core/localiser.hpp"
+#include "quest/src/core/paulilogic.hpp"
 
 #include <vector>
 
@@ -370,8 +371,6 @@ void rightapplySwap(Qureg qureg, int qubit1, int qubit2) {
  * individual Paulis
  */
 
-extern PauliStr paulis_getShiftedPauliStr(PauliStr str, int pauliShift);
-
 extern "C" {
 
 void leftapplyPauliX(Qureg qureg, int target) {
@@ -437,8 +436,6 @@ void rightapplyPauliZ(Qureg qureg, int target) {
  * Pauli strings
  */
 
-extern bool paulis_hasOddNumY(PauliStr str);
-
 extern "C" {
 
 void leftapplyPauliStr(Qureg qureg, PauliStr str) {
@@ -453,7 +450,7 @@ void rightapplyPauliStr(Qureg qureg, PauliStr str) {
     validate_quregIsDensityMatrix(qureg, __func__);
     validate_pauliStrTargets(qureg, str, __func__);
 
-    qcomp factor = paulis_hasOddNumY(str)? -1 : 1; // undo transpose
+    qcomp factor = paulis_getSignOfPauliStrConj(str); // undo transpose
     str = paulis_getShiftedPauliStr(str, qureg.numQubits);
     localiser_statevec_anyCtrlPauliTensor(qureg, {}, {}, str, factor);
 }
@@ -481,7 +478,7 @@ void rightapplyPauliGadget(Qureg qureg, PauliStr str, qreal angle) {
     validate_quregIsDensityMatrix(qureg, __func__);
     validate_pauliStrTargets(qureg, str, __func__);
 
-    qreal factor = paulis_hasOddNumY(str)? -1 : 1;
+    qreal factor = paulis_getSignOfPauliStrConj(str);
     qreal phase = factor * util_getPhaseFromGateAngle(angle);
     str = paulis_getShiftedPauliStr(str, qureg.numQubits);
     localiser_statevec_anyCtrlPauliGadget(qureg, {}, {}, str, phase);
@@ -675,7 +672,7 @@ void rightapplyPauliStrSum(Qureg qureg, PauliStrSum sum, Qureg workspace) {
     // post-multiply each term in-turn, mixing into output qureg, then undo using idempotency
     for (qindex i=0; i<sum.numTerms; i++) {
         PauliStr str =  paulis_getShiftedPauliStr(sum.strings[i], qureg.numQubits);
-        qcomp factor = paulis_hasOddNumY(str)? -1 : 1; // undoes transpose
+        qcomp factor = paulis_getSignOfPauliStrConj(str); // undoes transpose
 
         localiser_statevec_anyCtrlPauliTensor(workspace, {}, {}, str, factor);
         localiser_statevec_setQuregToSuperposition(1, qureg, sum.coeffs[i], workspace, 0, workspace);

quest/src/api/operations.cpp

@@ -19,6 +19,7 @@
 #include "quest/src/core/localiser.hpp"
 #include "quest/src/core/bitwise.hpp"
 #include "quest/src/core/constants.hpp"
+#include "quest/src/core/paulilogic.hpp"
 
 #include <vector>
 
@@ -30,12 +31,6 @@ using std::vector;
  * PRVIATE UTILITIES
  */
 
-extern int paulis_getSignOfPauliStrConj(PauliStr str);
-
-extern bool paulis_isIdentity(PauliStr str);
-extern PauliStr paulis_getShiftedPauliStr(PauliStr str, int pauliShift);
-extern PauliStr paulis_getKetAndBraPauliStr(PauliStr str, Qureg qureg);
-
 // T can be CompMatr, CompMatr1, CompMatr2, DiagMatr, DiagMatr1, DiagMatr2
 template <class T>
 void validateAndApplyAnyCtrlAnyTargUnitaryMatrix(Qureg qureg, int* ctrls, int* states, int numCtrls, int* targs, int numTargs, T matr, const char* caller) {