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sys: time_units: Add Kconfig option for algorithm selection

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Add maximum timeout used for conversion to Kconfig. Option is used
to determine which conversion algorithm to use: faster but overflowing
earlier or slower without early overflow.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
This commit is contained in:
Krzysztof Chruscinski 2022-01-12 10:35:38 +01:00 • committed by Anas Nashif
commit 50c7c7b1e4
3 changed files with 37 additions and 0 deletions
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25
include/sys/time_units.h
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@ -64,6 +64,21 @@ static TIME_CONSTEXPR inline int sys_clock_hw_cycles_per_sec(void)
#endif
}
/** @internal
* Macro determines if fast conversion algorithm can be used. It checks if
* maximum timeout represented in source frequency domain and multiplied by
* target frequency fits in 64 bits.
*
* @param from_hz Source frequency.
* @param to_hz Target frequency.
*
* @retval true Use faster algorithm.
* @retval false Use algorithm preventing overflow of intermediate value.
*/
#define Z_TMCVT_USE_FAST_ALGO(from_hz, to_hz) \
((ceiling_fraction(CONFIG_SYS_CLOCK_MAX_TIMEOUT_DAYS * 24ULL * 3600ULL * from_hz, \
UINT32_MAX) * to_hz) <= UINT32_MAX)
/* Time converter generator gadget. Selects from one of three
* conversion algorithms: ones that take advantage when the
* frequencies are an integer ratio (in either direction), or a full
@ -131,7 +146,17 @@ static TIME_CONSTEXPR ALWAYS_INLINE uint64_t z_tmcvt(uint64_t t, uint32_t from_h
} else {
if (result32) {
return (uint32_t)((t * to_hz + off) / from_hz);
} else if (const_hz && Z_TMCVT_USE_FAST_ALGO(from_hz, to_hz)) {
/* Faster algorithm but source is first multiplied by target frequency
* and it can overflow even though final result would not overflow.
* Kconfig option shall prevent use of this algorithm when there is a
* risk of overflow.
*/
return ((t * to_hz + off) / from_hz);
} else {
/* Slower algorithm but input is first divided before being multiplied
* which prevents overflow of intermediate value.
*/
return (t / from_hz) * to_hz + ((t % from_hz) * to_hz + off) / from_hz;
}
}