54 lines
2.2 KiB
Go
54 lines
2.2 KiB
Go
// From https://github.com/jackpal/Taipei-Torrent
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// Copyright (c) 2010 Jack Palevich. All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package metainfo
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// For more context on why these numbers, see http://wiki.vuze.com/w/Torrent_Piece_Size
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const minimumPieceLength = 16 * 1024
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const targetPieceCountLog2 = 10
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const targetPieceCountMin = 1 << targetPieceCountLog2
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// Target piece count should be < targetPieceCountMax
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const targetPieceCountMax = targetPieceCountMin << 1
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// Choose a good piecelength.
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func ChoosePieceLength(totalLength int64) (pieceLength int64) {
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// Must be a power of 2.
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// Must be a multiple of 16KB
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// Prefer to provide around 1024..2048 pieces.
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pieceLength = minimumPieceLength
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pieces := totalLength / pieceLength
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for pieces >= targetPieceCountMax {
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pieceLength <<= 1
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pieces >>= 1
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}
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return
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}
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