Pull Stream

Esiur/Data/GVWIE/GroupInt32Codec.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Runtime.CompilerServices;
+using System.Collections;
+
+namespace Esiur.Data.GVWIE;
+
+public static class GroupInt32Codec
+{
+    // ----------------- Encoder -----------------
+    public static byte[] Encode(IList<int> values)
+    {
+        //var values = value as int[];
+
+        var dst = new List<byte>(values.Count * 2);
+        int i = 0;
+
+        while (i < values.Count)
+        {
+            uint zz = ZigZag32(values[i]);
+
+            // Fast path: single byte (MSB=0) when zigzag fits in 7 bits
+            if (zz <= 0x7Fu)
+            {
+                dst.Add((byte)zz);
+                i++;
+                continue;
+            }
+
+            // Group: up to 32 items sharing a common width (1..4 bytes)
+            int start = i;
+            int count = 1;
+            int width = WidthFromZigZag(zz);
+
+            while (count < 32 && (i + count) < values.Count)
+            {
+                uint z2 = ZigZag32(values[i + count]);
+                int w2 = WidthFromZigZag(z2);
+                width = Math.Max(width, w2); // widen as needed
+                count++;
+            }
+
+            // Header: 1 | (count-1)[5 bits] | (width-1)[2 bits]
+            byte header = 0x80;
+            header |= (byte)(((count - 1) & 0x1F) << 2);
+            header |= (byte)((width - 1) & 0x03);
+            dst.Add(header);
+
+            // Payload: 'count' zigzag values, LE, 'width' bytes each
+            for (int k = 0; k < count; k++)
+                WriteLE(dst, ZigZag32(values[start + k]), width);
+
+            i += count;
+        }
+
+        return dst.ToArray();
+    }
+
+    // ----------------- Decoder -----------------
+    public static int[] Decode(ReadOnlySpan<byte> src)
+    {
+        var result = new List<int>();
+        int pos = 0;
+
+        while (pos < src.Length)
+        {
+            byte h = src[pos++];
+
+            if ((h & 0x80) == 0)
+            {
+                // Fast path: 7-bit ZigZag in low bits
+                uint zz7 = (uint)(h & 0x7F);
+                result.Add(UnZigZag32(zz7));
+                continue;
+            }
+
+            int count = ((h >> 2) & 0x1F) + 1; // 1..32
+            int width = (h & 0x03) + 1;        // 1..4
+
+            for (int j = 0; j < count; j++)
+            {
+                uint raw = (uint)ReadLE(src, ref pos, width);
+                int val = UnZigZag32(raw);
+                result.Add(val);
+            }
+        }
+
+        return result.ToArray();
+    }
+
+    // ----------------- Helpers -----------------
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static uint ZigZag32(int v) => (uint)((v << 1) ^ (v >> 31));
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int UnZigZag32(uint u) => (int)((u >> 1) ^ (uint)-(int)(u & 1));
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int WidthFromZigZag(uint z)
+    {
+        if (z <= 0xFFu) return 1;
+        if (z <= 0xFFFFu) return 2;
+        if (z <= 0xFFFFFFu) return 3;
+        return 4;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void WriteLE(List<byte> dst, uint value, int width)
+    {
+        for (int i = 0; i < width; i++)
+            dst.Add((byte)((value >> (8 * i)) & 0xFF));
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static ulong ReadLE(ReadOnlySpan<byte> src, ref int pos, int width)
+    {
+        if ((uint)(pos + width) > (uint)src.Length)
+            throw new ArgumentException("Buffer underflow while reading group payload.");
+
+        ulong v = 0;
+        for (int i = 0; i < width; i++)
+            v |= (ulong)src[pos++] << (8 * i);
+        return v;
+    }
+}