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1 | /************************************************************************** |
| 2 | * Copyright(c) 1998-1999, ALICE Experiment at CERN, All rights reserved. * |
| 3 | * * |
| 4 | * Author: The ALICE Off-line Project. * |
| 5 | * Contributors are mentioned in the code where appropriate. * |
| 6 | * * |
| 7 | * Permission to use, copy, modify and distribute this software and its * |
| 8 | * documentation strictly for non-commercial purposes is hereby granted * |
| 9 | * without fee, provided that the above copyright notice appears in all * |
| 10 | * copies and that both the copyright notice and this permission notice * |
| 11 | * appear in the supporting documentation. The authors make no claims * |
| 12 | * about the suitability of this software for any purpose. It is * |
| 13 | * provided "as is" without express or implied warranty. * |
| 14 | **************************************************************************/ |
| 15 | |
| 16 | /* $Id$ */ |
| 17 | |
| 18 | /////////////////////////////////////////////////////////////////////////////// |
| 19 | /// |
| 20 | /// This is a service class for packing and unpacking bits in a 32 bit word. |
| 21 | /// |
| 22 | /////////////////////////////////////////////////////////////////////////////// |
| 23 | |
| 24 | #include <TError.h> |
| 25 | |
| 26 | #include "AliBitPacking.h" |
| 27 | |
| 28 | |
| 29 | ClassImp(AliBitPacking) |
| 30 | |
| 31 | |
| 32 | //_____________________________________________________________________________ |
| 33 | Bool_t AliBitPacking::PackWord(UInt_t data, UInt_t &word, |
| 34 | Int_t startBit, Int_t stopBit) |
| 35 | { |
| 36 | // Packs data into the word buffer from startBit bit up to stopBit bit |
| 37 | |
| 38 | // check that startBit and stopBit are reasonable |
| 39 | if (startBit > stopBit) { |
| 40 | ::Error("AliBitPacking::PackWord", |
| 41 | "startBit is larger than stopBit"); |
| 42 | return kFALSE; |
| 43 | } |
| 44 | if (stopBit > 31) { |
| 45 | ::Error("AliBitPacking::PackWord", |
| 46 | "stopBit exceeds valid range of 32 bits"); |
| 47 | return kFALSE; |
| 48 | } |
| 49 | |
| 50 | // create a word with the bits 0 to (stopBit-startBit) set |
| 51 | UInt_t bits = 0xFFFFFFFF; |
| 52 | if (stopBit-startBit < 31) bits = (1 << (stopBit-startBit+1)) - 1; |
| 53 | |
| 54 | // check that the data fits into the given bit range |
| 55 | if (data > bits){ |
| 56 | ::Error("AliBitPacking::PackWord", |
| 57 | "Word to be filled is not within desired length"); |
| 58 | return kFALSE; |
| 59 | } |
| 60 | |
| 61 | // clear the bits from startBit to stopBit |
| 62 | word &= (0xFFFFFFFF ^ (bits << startBit)); |
| 63 | |
| 64 | // fill in the data bits |
| 65 | word |= (data << startBit); |
| 66 | |
| 67 | return kTRUE; |
| 68 | } |
| 69 | |
| 70 | //_____________________________________________________________________________ |
| 71 | UInt_t AliBitPacking::UnpackWord(UInt_t word, Int_t startBit, Int_t stopBit) |
| 72 | { |
| 73 | // Unpacks data of stopBit-startBit+1 bits from word buffer starting from |
| 74 | // the position indicated by startBit |
| 75 | |
| 76 | // check that startBit and stopBit are reasonable |
| 77 | if (startBit > stopBit) { |
| 78 | ::Error("AliBitPacking::UnpackWord", |
| 79 | "startBit is larger than stopBit"); |
| 80 | return 0xFFFFFFFF; |
| 81 | } |
| 82 | if (stopBit > 31) { |
| 83 | ::Error("AliBitPacking::UnpackWord", |
| 84 | "stopBit exceeds valid range of 32 bits"); |
| 85 | return 0xFFFFFFFF; |
| 86 | } |
| 87 | |
| 88 | // create a word with the bits 0 to (stopBit-startBit) set |
| 89 | UInt_t bits = 0xFFFFFFFF; |
| 90 | if (stopBit-startBit < 31) bits = (1 << (stopBit-startBit+1)) - 1; |
| 91 | |
| 92 | // pick out the requested bits |
| 93 | return ((word >> startBit) & bits); |
| 94 | } |
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