add missed file

library/signed/src/Measurement.qs

@@ -0,0 +1,49 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+import Std.Diagnostics.Fact;
+import Operations.Invert2sSI;
+
+/// # Summary
+/// Measures a signed integer of a given width.
+/// If the width is 4, the qubit register will be measured as a 4-bit signed integer.
+/// This means that bit n is the sign bit, and bits n-1 to 0 are the integer value.
+/// If fewer than `width` qubits are provided, the remaining bits are assumed to be 0.
+/// For example, if qubit register `[q1, q2, q3]` is passed in, but the width is 5,
+/// the integer value will be measured as `[0, 0, q1, q2, q3]`, with the first 0 being
+/// the sign bit (positive). This is in contrast to the standard library `MeasureInteger`,
+/// which always measures unsigned integers up to and including 63 qubits in width.
+/// If the length of the qubit register passed in is greater than the width, this operation
+/// will throw an error.
+///
+/// # Input
+/// ## target
+/// A qubit register representing the signed integer to be measured.
+///
+/// ## width
+/// The width of the signed integer to be measured.
+operation MeasureSignedInteger(target : Qubit[], width : Int) : Int {
+    let nBits = Length(target);
+    Fact(nBits <= 64, $"`Length(target)` must be less than or equal to 64, but was {nBits}.");
+    Fact(nBits <= width, $"`Length(target)` must be less than or equal to `width`, but was {nBits}.");
+
+    mutable coefficient = 1;
+    let signBit = MResetZ(target[nBits - 1]);
+    if (signBit == One) {
+        Operations.Invert2sSI(target);
+        set coefficient = -1;
+    }
+
+    mutable number = 0;
+    for i in 0..nBits - 2 {
+        if (MResetZ(target[i]) == One) {
+            set number |||= 1 <<< i;
+        }
+    }
+
+    ResetAll(target);
+
+    number * coefficient
+}
+
+export MeasureSignedInteger;