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authorCassio Neri <cassio.neri@gmail.com>2021-06-22 22:36:16 +0100
committerThomas Gleixner <tglx@linutronix.de>2021-06-24 11:51:59 +0200
commit276010551664f73b6f1616dde471d6f0d63a73ba (patch)
tree36bdb68afbbc7088b00c1ea0c9c55e8693b16960 /crypto/geniv.c
parent4e82d2e20f3b11f253bc5c6e92f05ed3694a1ae3 (diff)
downloadlinux-276010551664f73b6f1616dde471d6f0d63a73ba.tar.bz2
time: Improve performance of time64_to_tm()
The current implementation of time64_to_tm() contains unnecessary loops, branches and look-up tables. The new one uses an arithmetic-based algorithm appeared in [1] and is approximately 3x faster (YMMV). The drawback is that the new code isn't intuitive and contains many 'magic numbers' (not unusual for this type of algorithm). However, [1] justifies all those numbers and, given this function's history, the code is unlikely to need much maintenance, if any at all. Add a KUnit test for it which checks every day in a 160,000 years interval centered at 1970-01-01 against the expected result. [1] Neri, Schneider, "Euclidean Affine Functions and Applications to Calendar Algorithms". https://arxiv.org/abs/2102.06959 Signed-off-by: Cassio Neri <cassio.neri@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com
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