Added PauliArrayAsInt() and tests.

src/QirRuntime/test/QIR-static/qir-test-other.cpp

@@ -3,7 +3,20 @@
 
 #include "catch.hpp"
 
-extern "C" uint64_t Microsoft__Quantum__Testing__QIR__Other__ParityTest__body();        // NOLINT
+extern "C" uint64_t Microsoft__Quantum__Testing__QIR__Other__ParityTest__body();                // NOLINT
+extern "C" uint64_t Microsoft__Quantum__Testing__QIR__Other__PauliArrayAsIntTest__body();       // NOLINT
+extern "C" uint64_t Microsoft__Quantum__Testing__QIR__Other__PauliArrayAsIntFailTest__body();   // NOLINT
+
+TEST_CASE("QIR: Other.PauliArrayAsIntFail", "[qir.Other][qir.Other.PauliArrayAsIntFail]")
+{
+    REQUIRE_THROWS(Microsoft__Quantum__Testing__QIR__Other__PauliArrayAsIntFailTest__body());
+}
+
+TEST_CASE("QIR: Other.PauliArrayAsInt", "[qir.Other][qir.Other.PauliArrayAsInt]")
+{
+    REQUIRE(0 == Microsoft__Quantum__Testing__QIR__Other__PauliArrayAsIntTest__body());
+}
+
 
 TEST_CASE("QIR: Other.Parity", "[qir.Other][qir.Other.Parity]")
 {

src/QirRuntime/test/QIR-static/qsharp/qir-test-arrays.qs

@@ -55,6 +55,8 @@ namespace Microsoft.Quantum.Testing.QIR {
             let res17 = ArcCosTest();
             let res18 = ArcTanTest();
             let res19 = ParityTest();
+            let res20 = PauliArrayAsIntTest();
+            let res21 = PauliArrayAsIntFailTest();
             MessageTest("Test");
 
             // Conditionals:

src/QirRuntime/test/QIR-static/qsharp/qir-test-other.qs

@@ -4,10 +4,32 @@
 namespace Microsoft.Quantum.Testing.QIR.Other {
 
     open Microsoft.Quantum.Bitwise;
+    open Microsoft.Quantum.Convert;
+
+    function PauliArrayAsIntTest() : Int {
+        if 0 != PauliArrayAsInt([PauliI]) { return  1; }   // The return value indicates which test case has failed.
+        if 1 != PauliArrayAsInt([PauliX]) { return  2; }
+        if 3 != PauliArrayAsInt([PauliY]) { return  3; }
+        if 2 != PauliArrayAsInt([PauliZ]) { return  4; }
+
+        if 0x2310 != PauliArrayAsInt(
+            [PauliI, PauliI,  PauliX, PauliI,  PauliY, PauliI,  PauliZ, PauliI]) { return  5; }
+
+        // The Pauli array items are default-initialized to PauliI.
+        if 0 != PauliArrayAsInt(new Pauli[31]) { return  6; }   // Todo: Replace `new Pauli[31]` with `[PauliI, size=31]` when that is implemented.
+
+        if 0x3000000000000000 != PauliArrayAsInt(new Pauli[31] w/ 30 <- PauliY) { return  7; }
+
+        return 0;
+    }
+
+    function PauliArrayAsIntFailTest() : Int {
+        return PauliArrayAsInt(new Pauli[32]);   // Must fail/throw.
+    }
 
     function ParityTest() : Int {
         //function Parity (a : Int) : Int
-        if 0 != Parity(0)                       { return  1; }
+        if 0 != Parity(0)                       { return  1; }  // The return value indicates which test case has failed.
         if 1 != Parity(1)                       { return  2; }
         if 1 != Parity(2)                       { return  3; }
         if 0 != Parity(3)                       { return  4; }
@@ -23,5 +45,4 @@ namespace Microsoft.Quantum.Testing.QIR.Other {
 
         return 0;
     }
-
 }

src/Simulation/QSharpFoundation/Convert/Convert.cs

@@ -159,42 +159,4 @@ public Native(IOperationFactory m) : base(m) { }
         }
     }
 
-    public partial class PauliArrayAsInt
-    {
-        public class Native : PauliArrayAsInt
-        {
-            static long PauliBitsFunc(IQArray<Pauli> pauli)
-            {
-                if (pauli.Length > 31) { throw new ExecutionFailException("Cannot pack bits of Pauli array longer than 31"); }
-                ulong res = 0;
-                for (long i = pauli.Length - 1; i >= 0; --i)
-                {
-                    res <<= 2;
-                    if (pauli[i] == Pauli.PauliZ)
-                    {
-                        res |= 2;
-                    }
-                    else if (pauli[i] == Pauli.PauliX)
-                    {
-                        res |= 1;
-                    }
-                    else if (pauli[i] == Pauli.PauliY)
-                    {
-                        res |= 3;
-                    }
-                    else if (pauli[i] == Pauli.PauliI)
-                    {
-                    }
-                    else
-                    {
-                        System.Diagnostics.Debug.Assert(false, "this line should never be reached");
-                    }
-                }
-                return System.Convert.ToInt64(res);
-            }
-
-            public Native(IOperationFactory m) : base(m) { }
-            public override Func<IQArray<Pauli>, long> __Body__ => PauliBitsFunc;
-        }
-    }
 }

src/Simulation/QSharpFoundation/Convert/Convert.qs

@@ -164,7 +164,21 @@ namespace Microsoft.Quantum.Convert {
     /// the mappings of each Pauli operator in big-endian order
     /// `bits(Pn) ... bits(P0)`.
     function PauliArrayAsInt(paulis : Pauli[]) : Int {
-        body intrinsic;
+        let len = Length(paulis);
+        if len > 31 {
+            fail $"Cannot pack bits of Pauli array longer than 31 (got {len}).";
+        }
+
+        mutable result = 0;
+        for p in paulis[(len-1)..-1..0] {
+            set result <<<= 2;
+            if   p == PauliI { set result += 0; }
+            elif p == PauliX { set result += 1; }
+            elif p == PauliY { set result += 3; }
+            elif p == PauliZ { set result += 2; }
+            else { fail $"Unexpected Pauli value {p}."; }
+        }
+        return result;
     }
 
 }