Files
QuanTAlib/lib/core/simd/SimdExtensions.cs
T
Miha Kralj d7dbd7078a Refactor event handling and improve argument validation across indicators
- Updated event handler signatures to use TValueEventArgs for consistency in Mama, Mgdi, Pwma, Rma, Sma, Ssf, Super, T3, Tema, Trima, Usf, Vidya, Wma, and Atr classes.
- Enhanced argument validation by specifying parameter names in exceptions for clarity.
- Adjusted tests to align with new event handler signatures.
- Improved code readability and maintainability by using structured records and lambda expressions.
2025-12-27 15:46:28 -08:00

714 lines
25 KiB
C#

using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.Arm;
using System.Runtime.Intrinsics.X86;
namespace QuanTAlib;
/// <summary>
/// SIMD-accelerated extension methods for high-performance array operations.
/// Uses Vector<T> for 4-8x speedup on supported hardware with automatic scalar fallback.
/// </summary>
public static class SimdExtensions
{
// Internal scalar implementations for testability
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static bool ContainsNonFiniteScalar(ReadOnlySpan<double> span)
{
for (int i = 0; i < span.Length; i++)
{
if (!double.IsFinite(span[i]))
return true;
}
return false;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static double SumScalar(ReadOnlySpan<double> span)
{
double scalar = 0.0;
for (int i = 0; i < span.Length; i++)
scalar += span[i];
return scalar;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static double MinScalar(ReadOnlySpan<double> span)
{
if (span.Length == 0)
throw new ArgumentException("Span must not be empty", nameof(span));
double min = span[0];
for (int i = 1; i < span.Length; i++)
{
if (span[i] < min)
min = span[i];
}
return min;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static double MaxScalar(ReadOnlySpan<double> span)
{
if (span.Length == 0)
throw new ArgumentException("Span must not be empty", nameof(span));
double max = span[0];
for (int i = 1; i < span.Length; i++)
{
if (span[i] > max)
max = span[i];
}
return max;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static double VarianceScalar(ReadOnlySpan<double> span, double mean)
{
double sumSquares = 0.0;
for (int i = 0; i < span.Length; i++)
{
double diff = span[i] - mean;
sumSquares += diff * diff;
}
return sumSquares / (span.Length - 1);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static (double Min, double Max) MinMaxScalar(ReadOnlySpan<double> span)
{
double scalarMin = span[0];
double scalarMax = span[0];
for (int i = 1; i < span.Length; i++)
{
if (span[i] < scalarMin) scalarMin = span[i];
if (span[i] > scalarMax) scalarMax = span[i];
}
return (scalarMin, scalarMax);
}
/// <summary>
/// Checks if span contains any non-finite values (NaN or Infinity).
/// Returns true if any non-finite value is found.
/// Uses SIMD: NaN detected via v != v (NaN is the only value where this is true),
/// Infinity detected via |v| > MaxValue comparison.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static bool ContainsNonFinite(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return false;
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
int i = 0;
var maxValue = new Vector<double>(double.MaxValue);
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
// NaN check: NaN != NaN, so Vector.Equals(v, v) will be false for NaN lanes
var nanCheck = Vector.Equals(vector, vector);
if (!nanCheck.Equals(Vector<long>.AllBitsSet))
return true;
// Infinity check: |v| > MaxValue (Infinity has magnitude > MaxValue)
var absVec = Vector.Abs(vector);
var infCheck = Vector.GreaterThan(absVec, maxValue);
if (!infCheck.Equals(Vector<long>.Zero))
return true;
}
for (; i < span.Length; i++)
{
if (!double.IsFinite(span[i]))
return true;
}
return false;
}
return ContainsNonFiniteScalar(span);
}
/// <summary>
/// Calculates sum using SIMD vectorization when available.
/// 4-8x faster than scalar loop on AVX2/AVX-512 hardware.
/// Returns NaN if any input value is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double SumSIMD(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return 0.0;
// Guard against non-finite inputs
if (span.ContainsNonFinite()) return double.NaN;
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
Vector<double> sum = Vector<double>.Zero;
int vectorSize = Vector<double>.Count;
int i = 0;
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
sum += vector;
}
double result = 0.0;
for (int j = 0; j < vectorSize; j++)
result += sum[j];
for (; i < span.Length; i++)
result += span[i];
return result;
}
return SumScalar(span);
}
/// <summary>
/// Calculates minimum value using SIMD vectorization when available.
/// 4-6x faster than scalar loop on AVX2/AVX-512 hardware.
/// Returns NaN if any input value is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double MinSIMD(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return double.NaN;
if (span.Length == 1) return span[0];
// Guard against non-finite inputs
if (span.ContainsNonFinite()) return double.NaN;
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
var minVec = new Vector<double>(span[..vectorSize]);
int i = vectorSize;
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
minVec = Vector.Min(minVec, vector);
}
double result = minVec[0];
for (int j = 1; j < vectorSize; j++)
{
if (minVec[j] < result)
result = minVec[j];
}
for (; i < span.Length; i++)
{
if (span[i] < result)
result = span[i];
}
return result;
}
return MinScalar(span);
}
/// <summary>
/// Calculates maximum value using SIMD vectorization when available.
/// 4-6x faster than scalar loop on AVX2/AVX-512 hardware.
/// Returns NaN if any input value is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double MaxSIMD(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return double.NaN;
if (span.Length == 1) return span[0];
// Guard against non-finite inputs
if (span.ContainsNonFinite()) return double.NaN;
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
var maxVec = new Vector<double>(span[..vectorSize]);
int i = vectorSize;
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
maxVec = Vector.Max(maxVec, vector);
}
double result = maxVec[0];
for (int j = 1; j < vectorSize; j++)
{
if (maxVec[j] > result)
result = maxVec[j];
}
for (; i < span.Length; i++)
{
if (span[i] > result)
result = span[i];
}
return result;
}
return MaxScalar(span);
}
/// <summary>
/// Calculates average using SIMD vectorization when available.
/// 4-8x faster than scalar loop on AVX2/AVX-512 hardware.
/// Returns NaN if any input value is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double AverageSIMD(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return double.NaN;
// SumSIMD already guards against non-finite, which will propagate NaN
return span.SumSIMD() / span.Length;
}
/// <summary>
/// Calculates variance using a two-pass SIMD variant that computes the mean first (via AverageSIMD) and then sums squared differences to produce variance.
/// Note that this is not the single-pass Welford algorithm.
/// Returns NaN if any input value is non-finite or if mean is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double VarianceSIMD(this ReadOnlySpan<double> span, double? mean = null)
{
if (span.Length < 2) return double.NaN;
double m;
if (mean.HasValue)
{
if (span.ContainsNonFinite()) return double.NaN;
m = mean.Value;
}
else
{
m = span.AverageSIMD();
}
if (!double.IsFinite(m)) return double.NaN;
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
var meanVec = new Vector<double>(m);
Vector<double> sumSq = Vector<double>.Zero;
int vectorSize = Vector<double>.Count;
int i = 0;
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
var diff = vector - meanVec;
sumSq += diff * diff;
}
double result = 0.0;
for (int j = 0; j < vectorSize; j++)
result += sumSq[j];
for (; i < span.Length; i++)
{
double diff = span[i] - m;
result += diff * diff;
}
return result / (span.Length - 1);
}
return VarianceScalar(span, m);
}
/// <summary>
/// Calculates standard deviation using SIMD vectorization.
/// Returns NaN if any input value is non-finite or if mean is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double StdDevSIMD(this ReadOnlySpan<double> span, double? mean = null)
{
// VarianceSIMD already guards against non-finite, which will propagate NaN through Sqrt
return Math.Sqrt(span.VarianceSIMD(mean));
}
/// <summary>
/// Finds both min and max in a single pass using SIMD vectorization.
/// More efficient than calling MinSIMD and MaxSIMD separately.
/// Returns (NaN, NaN) if any input value is non-finite.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static (double Min, double Max) MinMaxSIMD(this ReadOnlySpan<double> span)
{
if (span.IsEmpty) return (double.NaN, double.NaN);
if (span.Length == 1) return (span[0], span[0]);
// Guard against non-finite inputs
if (span.ContainsNonFinite()) return (double.NaN, double.NaN);
if (Vector.IsHardwareAccelerated && span.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
var minVec = new Vector<double>(span[..vectorSize]);
var maxVec = minVec;
int i = vectorSize;
for (; i <= span.Length - vectorSize; i += vectorSize)
{
var vector = new Vector<double>(span.Slice(i, vectorSize));
minVec = Vector.Min(minVec, vector);
maxVec = Vector.Max(maxVec, vector);
}
double min = minVec[0];
double max = maxVec[0];
for (int j = 1; j < vectorSize; j++)
{
if (minVec[j] < min) min = minVec[j];
if (maxVec[j] > max) max = maxVec[j];
}
for (; i < span.Length; i++)
{
if (span[i] < min) min = span[i];
if (span[i] > max) max = span[i];
}
return (min, max);
}
return MinMaxScalar(span);
}
/// <summary>
/// Element-wise addition of two spans using SIMD.
/// result[i] = left[i] + right[i]
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static void Add(ReadOnlySpan<double> left, ReadOnlySpan<double> right, Span<double> result)
{
if (left.Length != right.Length || left.Length != result.Length)
throw new ArgumentException("All spans must have the same length", nameof(result));
int i = 0;
if (Vector.IsHardwareAccelerated && left.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
for (; i <= left.Length - vectorSize; i += vectorSize)
{
var vLeft = new Vector<double>(left.Slice(i, vectorSize));
var vRight = new Vector<double>(right.Slice(i, vectorSize));
(vLeft + vRight).CopyTo(result.Slice(i, vectorSize));
}
}
for (; i < left.Length; i++)
{
result[i] = left[i] + right[i];
}
}
/// <summary>
/// Element-wise subtraction of two spans using SIMD.
/// result[i] = left[i] - right[i]
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static void Subtract(ReadOnlySpan<double> left, ReadOnlySpan<double> right, Span<double> result)
{
if (left.Length != right.Length || left.Length != result.Length)
throw new ArgumentException("All spans must have the same length", nameof(result));
int i = 0;
if (Vector.IsHardwareAccelerated && left.Length >= Vector<double>.Count)
{
int vectorSize = Vector<double>.Count;
for (; i <= left.Length - vectorSize; i += vectorSize)
{
var vLeft = new Vector<double>(left.Slice(i, vectorSize));
var vRight = new Vector<double>(right.Slice(i, vectorSize));
(vLeft - vRight).CopyTo(result.Slice(i, vectorSize));
}
}
for (; i < left.Length; i++)
{
result[i] = left[i] - right[i];
}
}
/// <summary>
/// Calculates the dot product of two spans using SIMD intrinsics.
/// Supports AVX512, AVX2, and NEON (ARM64).
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static double DotProduct(this ReadOnlySpan<double> a, ReadOnlySpan<double> b)
{
if (a.Length != b.Length)
throw new ArgumentException("Spans must have equal length", nameof(b));
if (a.IsEmpty) return 0.0;
int len = a.Length;
// Fast path for very small kernels (avoid SIMD overhead)
if (len <= 3)
{
ref double aRef = ref MemoryMarshal.GetReference(a);
ref double bRef = ref MemoryMarshal.GetReference(b);
double sum = aRef * bRef;
if (len > 1) sum += Unsafe.Add(ref aRef, 1) * Unsafe.Add(ref bRef, 1);
if (len > 2) sum += Unsafe.Add(ref aRef, 2) * Unsafe.Add(ref bRef, 2);
return sum;
}
if (Avx512F.IsSupported)
return DotProductAvx512(a, b);
if (Avx2.IsSupported)
return DotProductAvx2(a, b);
if (AdvSimd.Arm64.IsSupported)
return DotProductNeon(a, b);
double s1 = 0, s2 = 0, s3 = 0, s4 = 0;
ref double ar = ref MemoryMarshal.GetReference(a);
ref double br = ref MemoryMarshal.GetReference(b);
int i = 0;
// Unroll scalar loop with 4 accumulators to break dependency chains
for (; i <= len - 4; i += 4)
{
s1 += Unsafe.Add(ref ar, i) * Unsafe.Add(ref br, i);
s2 += Unsafe.Add(ref ar, i + 1) * Unsafe.Add(ref br, i + 1);
s3 += Unsafe.Add(ref ar, i + 2) * Unsafe.Add(ref br, i + 2);
s4 += Unsafe.Add(ref ar, i + 3) * Unsafe.Add(ref br, i + 3);
}
double s = s1 + s2 + s3 + s4;
for (; i < len; i++)
{
s += Unsafe.Add(ref ar, i) * Unsafe.Add(ref br, i);
}
return s;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static double DotProductAvx512(ReadOnlySpan<double> a, ReadOnlySpan<double> b)
{
int len = a.Length;
int i = 0;
Vector512<double> vSum = Vector512<double>.Zero;
Vector512<double> vSum2 = Vector512<double>.Zero;
Vector512<double> vSum3 = Vector512<double>.Zero;
Vector512<double> vSum4 = Vector512<double>.Zero;
ref double aRef = ref MemoryMarshal.GetReference(a);
ref double bRef = ref MemoryMarshal.GetReference(b);
// Unroll loop: Process 32 doubles (4 vectors) at a time
if (len >= 32)
{
for (; i <= len - 32; i += 32)
{
var va1 = Vector512.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb1 = Vector512.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
var va2 = Vector512.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 8));
var vb2 = Vector512.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 8));
var va3 = Vector512.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 16));
var vb3 = Vector512.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 16));
var va4 = Vector512.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 24));
var vb4 = Vector512.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 24));
vSum = Avx512F.FusedMultiplyAdd(va1, vb1, vSum);
vSum2 = Avx512F.FusedMultiplyAdd(va2, vb2, vSum2);
vSum3 = Avx512F.FusedMultiplyAdd(va3, vb3, vSum3);
vSum4 = Avx512F.FusedMultiplyAdd(va4, vb4, vSum4);
}
}
// Process remaining vectors (8 doubles at a time)
for (; i <= len - 8; i += 8)
{
var va = Vector512.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb = Vector512.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
vSum = Avx512F.FusedMultiplyAdd(va, vb, vSum);
}
// Combine accumulators
vSum = Avx512F.Add(vSum, vSum2);
vSum3 = Avx512F.Add(vSum3, vSum4);
vSum = Avx512F.Add(vSum, vSum3);
Vector256<double> v256 = Avx.Add(vSum.GetLower(), vSum.GetUpper());
Vector128<double> lower = v256.GetLower();
Vector128<double> upper = v256.GetUpper();
Vector128<double> combined = Sse2.Add(lower, upper);
double sum = combined.GetElement(0) + combined.GetElement(1);
// Scalar remainder
for (; i < len; i++)
{
sum += Unsafe.Add(ref aRef, i) * Unsafe.Add(ref bRef, i);
}
return sum;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static double DotProductAvx2(ReadOnlySpan<double> a, ReadOnlySpan<double> b)
{
int len = a.Length;
int i = 0;
Vector256<double> vSum = Vector256<double>.Zero;
Vector256<double> vSum2 = Vector256<double>.Zero;
Vector256<double> vSum3 = Vector256<double>.Zero;
Vector256<double> vSum4 = Vector256<double>.Zero;
ref double aRef = ref MemoryMarshal.GetReference(a);
ref double bRef = ref MemoryMarshal.GetReference(b);
// Unroll loop: Process 16 doubles (4 vectors) at a time
if (len >= 16)
{
for (; i <= len - 16; i += 16)
{
var va1 = Vector256.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb1 = Vector256.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
var va2 = Vector256.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 4));
var vb2 = Vector256.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 4));
var va3 = Vector256.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 8));
var vb3 = Vector256.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 8));
var va4 = Vector256.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 12));
var vb4 = Vector256.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 12));
if (Fma.IsSupported)
{
vSum = Fma.MultiplyAdd(va1, vb1, vSum);
vSum2 = Fma.MultiplyAdd(va2, vb2, vSum2);
vSum3 = Fma.MultiplyAdd(va3, vb3, vSum3);
vSum4 = Fma.MultiplyAdd(va4, vb4, vSum4);
}
else
{
vSum = Avx.Add(vSum, Avx.Multiply(va1, vb1));
vSum2 = Avx.Add(vSum2, Avx.Multiply(va2, vb2));
vSum3 = Avx.Add(vSum3, Avx.Multiply(va3, vb3));
vSum4 = Avx.Add(vSum4, Avx.Multiply(va4, vb4));
}
}
}
// Process remaining vectors (4 doubles at a time)
for (; i <= len - 4; i += 4)
{
var va = Vector256.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb = Vector256.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
vSum = Fma.IsSupported
? Fma.MultiplyAdd(va, vb, vSum)
: Avx.Add(vSum, Avx.Multiply(va, vb));
}
// Combine accumulators
vSum = Avx.Add(vSum, vSum2);
vSum3 = Avx.Add(vSum3, vSum4);
vSum = Avx.Add(vSum, vSum3);
// Horizontal sum
Vector128<double> lower = vSum.GetLower();
Vector128<double> upper = vSum.GetUpper();
Vector128<double> combined = Sse2.Add(lower, upper);
double sum = combined.GetElement(0) + combined.GetElement(1);
// Process remaining elements (scalar)
for (; i < len; i++)
{
sum += Unsafe.Add(ref aRef, i) * Unsafe.Add(ref bRef, i);
}
return sum;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static double DotProductNeon(ReadOnlySpan<double> a, ReadOnlySpan<double> b)
{
int len = a.Length;
int i = 0;
Vector128<double> vSum = Vector128<double>.Zero;
Vector128<double> vSum2 = Vector128<double>.Zero;
Vector128<double> vSum3 = Vector128<double>.Zero;
Vector128<double> vSum4 = Vector128<double>.Zero;
ref double aRef = ref MemoryMarshal.GetReference(a);
ref double bRef = ref MemoryMarshal.GetReference(b);
// Unroll loop: Process 8 doubles (4 vectors) at a time
if (len >= 8)
{
for (; i <= len - 8; i += 8)
{
var va1 = Vector128.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb1 = Vector128.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
var va2 = Vector128.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 2));
var vb2 = Vector128.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 2));
var va3 = Vector128.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 4));
var vb3 = Vector128.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 4));
var va4 = Vector128.LoadUnsafe(ref Unsafe.Add(ref aRef, i + 6));
var vb4 = Vector128.LoadUnsafe(ref Unsafe.Add(ref bRef, i + 6));
// NEON has FMA on ARM64
// Since we are inside DotProductNeon which is guarded by AdvSimd.Arm64.IsSupported,
// we can assume Arm64 support.
vSum = AdvSimd.Arm64.FusedMultiplyAdd(vSum, va1, vb1);
vSum2 = AdvSimd.Arm64.FusedMultiplyAdd(vSum2, va2, vb2);
vSum3 = AdvSimd.Arm64.FusedMultiplyAdd(vSum3, va3, vb3);
vSum4 = AdvSimd.Arm64.FusedMultiplyAdd(vSum4, va4, vb4);
}
}
// Process remaining vectors (2 doubles at a time)
for (; i <= len - 2; i += 2)
{
var va = Vector128.LoadUnsafe(ref Unsafe.Add(ref aRef, i));
var vb = Vector128.LoadUnsafe(ref Unsafe.Add(ref bRef, i));
vSum = AdvSimd.Arm64.FusedMultiplyAdd(vSum, va, vb);
}
// Combine accumulators
vSum = AdvSimd.Arm64.Add(vSum, vSum2);
vSum3 = AdvSimd.Arm64.Add(vSum3, vSum4);
vSum = AdvSimd.Arm64.Add(vSum, vSum3);
// Horizontal sum (NEON has pairwise add)
double sum = AdvSimd.Arm64.AddPairwiseScalar(vSum).ToScalar();
// Scalar remainder (0-1 elements)
for (; i < len; i++)
{
sum += Unsafe.Add(ref aRef, i) * Unsafe.Add(ref bRef, i);
}
return sum;
}
}