67 lines
2.7 KiB
C
67 lines
2.7 KiB
C
/*
|
|
* 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)
|