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The CRC-T10DIF algorithm produces a 16-bit CRC, and this is reflected in the folding coefficients, which are also only 16 bits wide. This means that the polynomial multiplications involving these coefficients can be performed using 8-bit long polynomial multiplication (8x8 -> 16) in only a few steps, and this is an instruction that is part of the base NEON ISA, which is all most real ARMv7 cores implement. (The 64-bit PMULL instruction is part of the crypto extensions, which are only implemented by 64-bit cores) The final reduction is a bit more involved, but we can delegate that to the generic CRC-T10DIF implementation after folding the entire input into a 16 byte vector. This results in a speedup of around 6.6x on Cortex-A72 running in 32-bit mode. On Cortex-A8 (BeagleBone White), the results are substantially better than that, but not sufficiently reproducible (with tcrypt) to quote a number here. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> |
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