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
appea

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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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time: Add missing colons for parameter documentation of time64_to_tm()

Address these kernel-doc warnings:

kernel/time/timeconv.c:79: warning: Function parameter or member
'totalsecs' not describe

time: Add missing colons for parameter documentation of time64_to_tm()

Address these kernel-doc warnings:

kernel/time/timeconv.c:79: warning: Function parameter or member
'totalsecs' not described in 'time64_to_tm'
kernel/time/timeconv.c:79: warning: Function parameter or member
'offset' not described in 'time64_to_tm'
kernel/time/timeconv.c:79: warning: Function parameter or member
'result' not described in 'time64_to_tm'

The parameters are described but lack colons after the parameter name.

[ tglx: Massaged changelog ]

Signed-off-by: Alex Shi <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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time: Add SPDX license identifiers

Update the time(r) core files files with the correct SPDX license
identifier based on the license text in the file itself. The SPDX
identifier is a legally binding

time: Add SPDX license identifiers

Update the time(r) core files files with the correct SPDX license
identifier based on the license text in the file itself. The SPDX
identifier is a legally binding shorthand, which can be used instead of the
full boiler plate text.

This work is based on a script and data from Philippe Ombredanne, Kate
Stewart and myself. The data has been created with two independent license
scanners and manual inspection.

The following files do not contain any direct license information and have
been omitted from the big initial SPDX changes:

timeconst.bc: The .bc files were not touched
time.c, timer.c, timekeeping.c: Licence was deduced from EXPORT_SYMBOL_GPL

As those files do not contain direct license references they fall under the
project license, i.e. GPL V2 only.

Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Kees Cook <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Acked-by: John Stultz <[email protected]>
Acked-by: Corey Minyard <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Kate Stewart <[email protected]>
Cc: Philippe Ombredanne <[email protected]>
Cc: Russell King <[email protected]>
Cc: Richard Cochran <[email protected]>
Cc: Nicolas Pitre <[email protected]>
Cc: David Riley <[email protected]>
Cc: Colin Cross <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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time: Add time64_to_tm()

time_to_tm() takes time_t as an argument.
time_t is not y2038 safe.
Add time64_to_tm() that takes time64_t as an argument
which is y2038 safe.
The plan is to eventually repl

time: Add time64_to_tm()

time_to_tm() takes time_t as an argument.
time_t is not y2038 safe.
Add time64_to_tm() that takes time64_t as an argument
which is y2038 safe.
The plan is to eventually replace all calls to time_to_tm()
by time64_to_tm().

Cc: Prarit Bhargava <[email protected]>
Cc: Richard Cochran <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Deepa Dinamani <[email protected]>
Signed-off-by: John Stultz <[email protected]>

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time: add function to convert between calendar time and broken-down time for universal use

There are many similar code in kernel for one object: convert time between
calendar time and broken-down ti

time: add function to convert between calendar time and broken-down time for universal use

There are many similar code in kernel for one object: convert time between
calendar time and broken-down time.

Here is some source I found:
fs/ncpfs/dir.c
fs/smbfs/proc.c
fs/fat/misc.c
fs/udf/udftime.c
fs/cifs/netmisc.c
net/netfilter/xt_time.c
drivers/scsi/ips.c
drivers/input/misc/hp_sdc_rtc.c
drivers/rtc/rtc-lib.c
arch/ia64/hp/sim/boot/fw-emu.c
arch/m68k/mac/misc.c
arch/powerpc/kernel/time.c
arch/parisc/include/asm/rtc.h
...

We can make a common function for this type of conversion, At least we
can get following benefit:

1: Make kernel simple and unify
2: Easy to fix bug in converting code
3: Reduce clone of code in future
For example, I'm trying to make ftrace display walltime,
this patch will make me easy.

This code is based on code from glibc-2.6

Signed-off-by: Zhao Lei <[email protected]>
Cc: OGAWA Hirofumi <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Andi Kleen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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