UnsafeSet.cs

// Copyright (c) 2022 Hafthor Stefansson
// Distributed under the MIT/X11 software license
// Ref: http://www.opensource.org/licenses/mit-license.php.
static unsafe void UnsafeSet(byte[] a, uint d, uint c, byte v) {
    unchecked {
        ushort v2 = (ushort)(v << 8 | v);
        uint v4 = (uint)v2 << 16 | v2;
        ulong v8 = (ulong)v4 << 32 | v4;
        fixed (byte* p = a) {
            byte* di = p + d;
            if (c >= 1 && (d & 1) != 0) { // word align
                *((byte*)di) = v; di++; c--; d++;
            }
            if (c >= 2 && (d & 2) != 0) { // dword align
                *((ushort*)di) = v2; di += 2; c -= 2; d += 2;
            }
            if (c >= 4 && (d & 4) != 0) { // qword align
                *((uint*)di) = v4; di += 4; c -= 4;
            }
            while (c >= 8) { // qword set
                *((ulong*)di) = v8; di += 8; c -= 8;
            }
            if (c >= 4) { // dword remainder
                *((uint*)di) = v4; di += 4; c -= 4;
            }
            if (c >= 2) { // word remainder
                *((ushort*)di) = v2; di += 2; c -= 2;
            }
            if (c >= 1) { // byte remainder
                *((byte*)di) = v; // di++; c--;
            }
        }
    }
}