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drivers: sensor: sgp40: fix rounding errors

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This fixes/improves the rounding errors that are introduced
through the truncation of integer division.

Signed-off-by: Leonard Pollak <leonardp@tr-host.de>
This commit is contained in:
Leonard Pollak 2021-08-27 16:30:36 +02:00 • committed by Anas Nashif
commit dcff99eeaf
1 changed files with 4 additions and 2 deletions
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6
drivers/sensor/sgp40/sgp40.c
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@ -71,7 +71,8 @@ static int sgp40_attr_set(const struct device *dev,
int32_t tmp; int32_t tmp;
tmp = CLAMP(val->val1, SGP40_COMP_MIN_T, SGP40_COMP_MAX_T); tmp = CLAMP(val->val1, SGP40_COMP_MIN_T, SGP40_COMP_MAX_T);
t_ticks = ((tmp + 45) * 65535) / 175; /* adding +87 to avoid most rounding errors through truncation */
t_ticks = (((tmp + 45) * 65535) + 87) / 175;
sys_put_be16(t_ticks, data->t_param); sys_put_be16(t_ticks, data->t_param);
data->t_param[2] = sgp40_compute_crc(t_ticks); data->t_param[2] = sgp40_compute_crc(t_ticks);
} }
@ -82,7 +83,8 @@ static int sgp40_attr_set(const struct device *dev,
int32_t tmp; int32_t tmp;
tmp = CLAMP(val->val1, SGP40_COMP_MIN_RH, SGP40_COMP_MAX_RH); tmp = CLAMP(val->val1, SGP40_COMP_MIN_RH, SGP40_COMP_MAX_RH);
rh_ticks = (tmp * 65535) / 100; /* adding +50 to eliminate rounding errors through truncation */
rh_ticks = ((tmp * 65535) + 50) / 100;
sys_put_be16(rh_ticks, data->rh_param); sys_put_be16(rh_ticks, data->rh_param);
data->rh_param[2] = sgp40_compute_crc(rh_ticks); data->rh_param[2] = sgp40_compute_crc(rh_ticks);
} }