ea8e48a679
According to my profiling of Qt Creator, qHash and the SHA-1 calculation are the hottest spots remaining in QtCore. The current qHash function is not really vectorizable. We could come up with a different algorithm that is more SIMD-friendly, but since we have the CRC32 instruction that can read 32- and 64-bit entities, we're set. This commit also updates the benchmark for QHash and benchmarks both the hashing function itself and the QHash class. The updated benchmarks for the CRC32 on my machine shows that the hashing function is *always* improved, but the hashing isn't always. In particular, the current algorithm is better for the "numbers" case, for which the data sample differs in very few bits. The new code is 33% slower for that particular case. On average, the improvement (including the "numbers" case) is: compared to qHash only QHash Qt 5.0 function 2.54x 1.06x Qt 4.x function 4.34x 1.34x Java function 2.71x 1.11x Test machine: Sandybridge Core i7-2620M @ 2.66 GHz with turbo disabled for the benchmarks Change-Id: Ia80b98c0e20d785816f7a7f6ddf40b4b302c7297 Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com> Reviewed-by: Lars Knoll <lars.knoll@digia.com> Reviewed-by: Thiago Macieira <thiago.macieira@intel.com> |
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