Add vDSP_vrsumD

Author: ptoffy

README.md

@@ -62,7 +62,7 @@ The package is structured as follows:
         - [x] `vDSP_dotprD` - Dot product of two vectors
         - [x] `vDSP_vlimD` - Limit a vector to a range
         - [c] `vDSP_vclipcD` - Clip a vector to a range
-        - [ ] `vDSP_vrsumD` - Recursive sum of a vector
+        - [x] `vDSP_vrsumD` - Recursive sum of a vector
         - [ ] `vDSP_vsortD` - Sort a vector
         - [ ] `vDSP_vrampD` - Ramp a vector
         - [ ] `vDSP.sum` - Sum of a vector

Sources/AccelerateLinux/VectorOps/VectorBasicOps.swift

@@ -313,4 +313,40 @@ public func vDSP_vclipcD(
         i += 1
     }
 }
+
+/// Performs running sum integration over a double-precision vector.
+/// - Parameters:
+///   - __A: Double-precision real input vector.
+///   - __IA: Address stride for A.
+///   - __S: Points to double-precision real input scalar: weighting factor.
+///   - __C: Double-precision real output vector.
+///   - __IC: Stride for C
+///   - __N: The number of elements to process.
+/// Integrates vector A using a running sum from vector C.
+/// Vector A is weighted by scalar *S and added to the previous output point.
+/// The first element from vector A is not used in the sum.
+public func vDSP_vrsumD(
+    _ __A: UnsafePointer<Double>,
+    _ __IA: vDSP_Stride,
+    _ __S: UnsafePointer<Double>,
+    _ __C: UnsafeMutablePointer<Double>,
+    _ __IC: vDSP_Stride,
+    _ __N: vDSP_Length
+) {
+    @discardableResult
+    func aux(
+        _ __A: UnsafePointer<Double>,
+        _ __IA: vDSP_Stride,
+        _ __S: UnsafePointer<Double>,
+        _ __C: UnsafeMutablePointer<Double>,
+        _ __IC: vDSP_Stride,
+        _ __N: vDSP_Length
+    ) -> Double {
+        if __N == 0 { return 0 }
+        __C[Int(__N) * __IC] += (__S.pointee * __A[Int(__N) * __IA]) + aux(__A, __IA, __S, __C, __IC, __N - 1)
+        return __C[Int(__N) * __IC]
+    }
+
+    aux(__A, __IA, __S, __C, __IC, __N)
+}
 #endif

Tests/AccelerateLinuxTests/VectorTests/VectorBasicOpsTests.swift

@@ -267,4 +267,22 @@ struct VectorBasicOpsTests {
         #expect(nLow == 2)
         #expect(nHigh == 1)
     }
+
+    @Test("vDSP_vrsum")
+    func vDSP_vrsumTest() {
+        let stride = 1
+        let n = 4
+
+        let a: [Double] = [1.0, 2.0, 3.0, 4.0]
+        var startValue: Double = 10.0
+        var c = [Double](repeating: 0.0, count: 4)
+
+        vDSP_vrsumD(
+            a, stride,
+            &startValue,
+            &c, stride,
+            vDSP_Length(n))
+
+        #expect(c == [0.0, 20.0, 50.0, 90.0])
+    }
 }