Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / cdf / src / WCF / Log / System / IO / Log / LogLogRecordHeader.cs / 1305376 / LogLogRecordHeader.cs
//------------------------------------------------------------------------------ // Copyright (c) Microsoft Corporation. All rights reserved. //----------------------------------------------------------------------------- namespace System.IO.Log { using System; [Flags] internal enum LogLogRecordFlags : ushort { Padding = 0x0001 } internal struct LogLogRecordHeader { public const int Size = 4; public const byte CurrentMajorVersion = 1; public const byte CurrentMinorVersion = 0; const int MajorVersionOffset = 0; const int MinorVersionOffset = 1; const int FlagsOffset = 2; byte[] bits; public LogLogRecordHeader(byte[] bits) { if (bits == null) bits = new byte[Size]; if (bits.Length < Size) { throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.LogCorrupt()); } this.bits = bits; } public byte[] Bits { get { return bits; } } public byte MajorVersion { get { return bits[MajorVersionOffset]; } set { bits[MajorVersionOffset] = value; } } public byte MinorVersion { /* get { return bits[MinorVersionOffset]; } */ set { bits[MinorVersionOffset] = value; } } public bool Padding { get { LogLogRecordFlags flags; flags = (LogLogRecordFlags)BitConverter.ToUInt16(bits, FlagsOffset); return (flags & LogLogRecordFlags.Padding) != 0; } set { LogLogRecordFlags flags; flags = (LogLogRecordFlags)BitConverter.ToUInt16(bits, FlagsOffset); if (value) flags |= LogLogRecordFlags.Padding; else flags &= ~LogLogRecordFlags.Padding; WriteUInt16((ushort)flags, bits, FlagsOffset); } } //+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ // LogLogRecordHeader was defined to track the reservations for individual records whose size may be // lesser than the actual reservation. CLFS doesn't track the actual amount of space consumed for a reservation // and tracks only the total reserved space. If we reserve 1 record of 10 bytes, we must consume all the // 10 bytes. For appending records with size less than the actual reserved amount IO.Log uses a header block with // necessary padding to match the reservation size. // Eg, if we reserves 1 record of 10 bytes, then writes 1 record of 5 bytes from reservation, // we add 5 bytes of padding, so that we consume the 10 byte reservation completely. // // 1 Byte 1 Byte 2 Bytes n Padding bytes. // --------------------------------------------------------------------------------------------- // | Major Version | Minor Version | Flags | Variable length Padding (Length + zeros) // | // --------------------------------------------------------------------------------------------- // EncodePaddingSize sets the padding length in header bits after the header fields. // Eg. The following output shows the values for each byte in the header for padding size from 0 to 6. // The byte after the flag contains the size of the padding needed and followed by zeros. // // 4 byte header + padding lenth + padding zeros // 1 0 0 0 // 1 0 1 0 1 // 1 0 1 0 2 0 // 1 0 1 0 3 0 0 // 1 0 1 0 4 0 0 0 // 1 0 1 0 5 0 0 0 0 // 1 0 1 0 6 0 0 0 0 0 public static void EncodePaddingSize(byte[] padding, int offset, int length) { int index = offset; int padSize = length; while(padSize != 0) { padding[index] = (byte)(padSize & 0x7F); padSize = padSize >> 7; if (padSize != 0) padding[index] |= 0x80; index++; } } // // DecodePaddingSize returns the padding length in the byte array. // The caller will then use it as an offset to get to the actual record. // unsafe public static long DecodePaddingSize(byte* data, long length) { uint padSize = 0; int shift = 0; while(length > 0) { padSize |= (uint)((*data & 0x7f) << shift); if (padSize > Int32.MaxValue) { throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(Error.LogCorrupt()); } shift += 7; if ((*data & 0x80) == 0) break; data++; length--; } return (long)padSize; } static void WriteUInt16(ushort value, byte[] where, int offset) { where[offset + 0] = (byte)((value & 0x00FF) >> 0); where[offset + 1] = (byte)((value & 0xFF00) >> 8); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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