/*+
−
* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.+
−
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.+
−
*+
−
* This code is free software; you can redistribute it and/or modify it+
−
* under the terms of the GNU General Public License version 2 only, as+
−
* published by the Free Software Foundation.+
−
*+
−
* This code is distributed in the hope that it will be useful, but WITHOUT+
−
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or+
−
* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License+
−
* version 2 for more details (a copy is included in the LICENSE file that+
−
* accompanied this code).+
−
*+
−
* You should have received a copy of the GNU General Public License version+
−
* 2 along with this work; if not, write to the Free Software Foundation,+
−
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.+
−
*+
−
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA+
−
* or visit www.oracle.com if you need additional information or have any+
−
* questions.+
−
*+
−
*/+
−
+
−
enum {+
−
  // S. Gueron / Information Processing Letters 112 (2012) 184+
−
  // shows than anything above 6K and below 32K is a good choice+
−
  // 32K does not deliver any further performance gains+
−
  // 6K=8*256 (*3 as we compute 3 blocks together)+
−
  //+
−
  // Thus selecting the smallest value so it could apply to the largest number+
−
  // of buffer sizes.+
−
  CRC32C_HIGH = 8 * 256,+
−
+
−
  // empirical+
−
  // based on ubench study using methodology described in+
−
  // V. Gopal et al. / Fast CRC Computation for iSCSI Polynomial Using CRC32 Instruction April 2011 8+
−
  //+
−
  // arbitrary value between 27 and 256+
−
  CRC32C_MIDDLE = 8 * 86,+
−
+
−
  // V. Gopal et al. / Fast CRC Computation for iSCSI Polynomial Using CRC32 Instruction April 2011 9+
−
  // shows that 240 and 1024 are equally good choices as the 216==8*27+
−
  //+
−
  // Selecting the smallest value which resulted in a significant performance improvement over+
−
  // sequential version+
−
  CRC32C_LOW = 8 * 27,+
−
+
−
  CRC32C_NUM_ChunkSizeInBytes = 3,+
−
+
−
  // We need to compute powers of 64N and 128N for each "chunk" size+
−
  CRC32C_NUM_PRECOMPUTED_CONSTANTS = ( 2 * CRC32C_NUM_ChunkSizeInBytes )+
−
};+
−
// Notes:+
−
// 1. Why we need to choose a "chunk" approach?+
−
// Overhead of computing a powers and powers of for an arbitrary buffer of size N is significant+
−
// (implementation approaches a library perf.)+
−
// 2. Why only 3 "chunks"?+
−
// Performance experiments results showed that a HIGH+LOW was not delivering a stable speedup+
−
// curve.+
−
//+
−
// Disclaimer:+
−
// If you ever decide to increase/decrease number of "chunks" be sure to modify+
−
// a) constants table generation (hotspot/src/cpu/x86/vm/stubRoutines_x86.cpp)+
−
// b) constant fetch from that table (macroAssembler_x86.cpp)+
−
// c) unrolled for loop (macroAssembler_x86.cpp)+
−