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Fix pressure_time calculation for SAC-rate

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The code was using bar, not atm to calculate the pressure_time
multiplier.  But SAC-rate is relative to atm.

We could do the correction at the end (and keep the pressure_time in
"bar-seconds"), but let's just use the expected units during the
integration.  Especially since this also makes a helper function to do
the calculations (with variables to keep the units obvious) instead of
having multi-line expressions that have the wrong units.

This fixes what I thought were rounding errors for the pressure graphs.
They were just unit confusion.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
This commit is contained in:
Linus Torvalds 2013-01-06 16:55:25 -08:00 • committed by Dirk Hohndel
parent 98ed131bda
commit 25209bfbb4
1 changed files with 17 additions and 2 deletions
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19
profile.c
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@ -1685,6 +1685,20 @@ static void setup_gas_sensor_pressure(struct dive *dive, struct divecomputer *dc
} while ((secondary = secondary->next) != NULL); } while ((secondary = secondary->next) != NULL);
} }
/*
* What's the pressure-time between two plot data entries?
* We're calculating the integral of pressure over time by
* adding these up.
*/
static inline double pressure_time(struct dive *dive, struct plot_data *a, struct plot_data *b)
{
int time = b->sec - a->sec;
int depth = (a->depth + b->depth)/2;
int mbar = depth_to_mbar(depth, dive);
return bar_to_atm(mbar / 1000.0) * time;
}
static void populate_pressure_information(struct dive *dive, struct divecomputer *dc, struct plot_info *pi) static void populate_pressure_information(struct dive *dive, struct divecomputer *dc, struct plot_info *pi)
{ {
int i, cylinderindex; int i, cylinderindex;
@ -1709,6 +1723,9 @@ static void populate_pressure_information(struct dive *dive, struct divecomputer
entry->same_cylinder = entry->cylinderindex == cylinderindex; entry->same_cylinder = entry->cylinderindex == cylinderindex;
cylinderindex = entry->cylinderindex; cylinderindex = entry->cylinderindex;
/* discrete integration of pressure over time to get the SAC rate equivalent */
current->pressure_time += pressure_time(dive, entry-1, entry);
/* track the segments per cylinder and their pressure/time integral */ /* track the segments per cylinder and their pressure/time integral */
if (!entry->same_cylinder) { if (!entry->same_cylinder) {
current = pr_track_alloc(SENSOR_PRESSURE(entry), entry->sec); current = pr_track_alloc(SENSOR_PRESSURE(entry), entry->sec);
@ -1724,8 +1741,6 @@ static void populate_pressure_information(struct dive *dive, struct divecomputer
} }
} }
/* finally, do the discrete integration to get the SAC rate equivalent */ /* finally, do the discrete integration to get the SAC rate equivalent */
current->pressure_time += (entry->sec - (entry-1)->sec) *
depth_to_mbar((entry->depth + (entry-1)->depth) / 2, dive) / 1000.0;
if (SENSOR_PRESSURE(entry)) { if (SENSOR_PRESSURE(entry)) {
current->end = SENSOR_PRESSURE(entry); current->end = SENSOR_PRESSURE(entry);
current->t_end = entry->sec; current->t_end = entry->sec;