drivers: sensor: ntc-thermistor: Simplify comp lookup

bsearch() tries to find the exact match for the key, otherwise it
returns NULL. However, here we want to find two elements our key lies
in-between. This requires some rather complicated logic that pretends
it found the exact match even if it didn't. Replace this with a simple
implementation of binary search.

Signed-off-by: Paweł Anikiel <pan@semihalf.com>

drivers/sensor/ntc_thermistor/ntc_thermistor.c

@@ -96,8 +96,6 @@ static int ntc_thermistor_init(const struct device *dev)
 }
 
 #define NTC_THERMISTOR_DEFINE0(inst, id, _comp, _n_comp)                                           \
-	static int compare_ohm_##id##inst(const void *key, const void *element);                   \
-                                                                                                   \
 	static struct ntc_thermistor_data ntc_thermistor_driver_##id##inst;                        \
                                                                                                    \
 	static const struct ntc_thermistor_config ntc_thermistor_cfg_##id##inst = {                \
@@ -112,17 +110,10 @@ static int ntc_thermistor_init(const struct device *dev)
 				.type = {                                                          \
 					.comp = _comp,                                             \
 					.n_comp = _n_comp,                                         \
-					.ohm_cmp = compare_ohm_##id##inst,                         \
 				},                                                                 \
 			},                                                                         \
 	};                                                                                         \
                                                                                                    \
-	static int compare_ohm_##id##inst(const void *key, const void *element)                    \
-	{                                                                                          \
-		return ntc_compensation_compare_ohm(                                               \
-			&ntc_thermistor_cfg_##id##inst.ntc_cfg.type, key, element);                \
-	}                                                                                          \
-                                                                                                   \
 	SENSOR_DEVICE_DT_INST_DEFINE(                                                              \
 		inst, ntc_thermistor_init, NULL, &ntc_thermistor_driver_##id##inst,                \
 		&ntc_thermistor_cfg_##id##inst, POST_KERNEL, CONFIG_SENSOR_INIT_PRIORITY,          \

drivers/sensor/ntc_thermistor/ntc_thermistor.h

@@ -17,7 +17,6 @@ struct ntc_compensation {
 struct ntc_type {
 	const struct ntc_compensation *comp;
 	int n_comp;
-	int (*ohm_cmp)(const void *key, const void *element);
 };
 
 struct ntc_config {
@@ -29,19 +28,6 @@ struct ntc_config {
 	struct ntc_type type;
 };
 
-/**
- * @brief Helper comparison function for bsearch for specific
- * ntc_type
- *
- * Ohms are sorted in descending order, perform comparison to find
- * interval indexes where key falls between
- *
- * @param type: Pointer to ntc_type table info
- * @param key: Key value bsearch is looking for
- * @param element: Array element bsearch is searching
- */
-int ntc_compensation_compare_ohm(const struct ntc_type *type, const void *key, const void *element);
-
 /**
  * @brief Converts ohm to temperature in milli centigrade
  *

drivers/sensor/ntc_thermistor/ntc_thermistor_calc.c

@@ -30,47 +30,6 @@ static int ntc_fixp_linear_interpolate(int x0, int y0, int x1, int y1, int x)
 	return y0 + ((y1 - y0) * (x - x0) / (x1 - x0));
 }
 
-/**
- * ntc_compensation_compare_ohm() - Helper comparison function for bsearch
- *
- * Ohms are sorted in descending order, perform comparison to find
- * interval indexes where key falls between
- *
- * @type: Pointer to ntc_type table info
- * @key: Key value bsearch is looking for
- * @element: Array element bsearch is searching
- */
-int ntc_compensation_compare_ohm(const struct ntc_type *type, const void *key, const void *element)
-{
-	int sgn = 0;
-	const struct ntc_compensation *ntc_key = key;
-	const struct ntc_compensation *element_val = element;
-	int element_idx = element_val - type->comp;
-
-	if (ntc_key->ohm > element_val->ohm) {
-		if (element_idx == 0) {
-			sgn = 0;
-		} else {
-			sgn = -1;
-		}
-	} else if (ntc_key->ohm == element_val->ohm) {
-		sgn = 0;
-	} else if (ntc_key->ohm < element_val->ohm) {
-		if (element_idx == (type->n_comp / 2) - 1) {
-			sgn = 0;
-		} else {
-			if (element_idx != (type->n_comp / 2) - 1 &&
-			    ntc_key->ohm > type->comp[element_idx + 1].ohm) {
-				sgn = 0;
-			} else {
-				sgn = 1;
-			}
-		}
-	}
-
-	return sgn;
-}
-
 /**
  * ntc_lookup_comp() - Finds indicies where ohm falls between
  *
@@ -80,18 +39,27 @@ int ntc_compensation_compare_ohm(const struct ntc_type *type, const void *key, c
  */
 static void ntc_lookup_comp(const struct ntc_type *type, unsigned int ohm, int *i_low, int *i_high)
 {
-	const struct ntc_compensation *ptr;
+	int low = 0;
-	struct ntc_compensation search_ohm_key = {.ohm = ohm};
+	int high = type->n_comp - 1;
 
-	ptr = bsearch(&search_ohm_key, type->comp, type->n_comp, sizeof(type->comp[0]),
+	if (ohm > type->comp[low].ohm) {
-		      type->ohm_cmp);
+		high = low;
-	if (ptr) {
+	} else if (ohm < type->comp[high].ohm) {
-		*i_low = ptr - type->comp;
+		low = high;
-		*i_high = *i_low + 1;
-	} else {
-		*i_low = 0;
-		*i_high = 0;
 	}
+
+	while (high - low > 1) {
+		int mid = (low + high) / 2;
+
+		if (ohm > type->comp[mid].ohm) {
+			high = mid;
+		} else {
+			low = mid;
+		}
+	}
+
+	*i_low = low;
+	*i_high = high;
 }
 
 /**