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| |
| 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) |