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cpucounter: Increase conversion accuracy

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The maximum frequency is UINT32_MAX.  Converted to a uint64_t variable
it can be shifted by 32.  The addition does not overflow since bin_per_s
- 1 is UINT32_MAX.
This commit is contained in:
Sebastian Huber
2021-01-26 15:29:36 +01:00
parent 9d2db27adf
commit c734e8660f
1 changed files with 4 additions and 3 deletions
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cpukit/sapi/src/cpucounterconverter.c
+4 -3
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@@ -42,19 +42,20 @@ int64_t rtems_counter_ticks_to_sbintime( rtems_counter_ticks ticks )
rtems_counter_ticks rtems_counter_sbintime_to_ticks( int64_t sbt )
{
return (rtems_counter_ticks) (((uint64_t) sbt * from_sbt_scaler) >> 31);
return (rtems_counter_ticks) (((uint64_t) sbt * from_sbt_scaler) >> 32);
}
void rtems_counter_initialize_converter( uint32_t frequency )
{
uint64_t ns_per_s = UINT64_C(1000000000);
uint64_t bin_per_s = UINT64_C(1) << 32;
uint64_t bin_freq = (uint64_t) frequency << 32;
to_ns_scaler = ((ns_per_s << 32) + frequency - 1) / frequency;
from_ns_scaler = ((UINT64_C(1) << 32) * frequency + ns_per_s - 1) / ns_per_s;
from_ns_scaler = (bin_freq + ns_per_s - 1) / ns_per_s;
to_sbt_scaler = ((bin_per_s << 31) + frequency - 1) / frequency;
from_sbt_scaler = ((UINT64_C(1) << 31) * frequency + bin_per_s - 1) / bin_per_s;
from_sbt_scaler = (bin_freq + bin_per_s - 1) / bin_per_s;
}
static void rtems_counter_sysinit( void )