#include <stdint.h>
#include <string.h>
#include <ctype.h>
+#include <math.h>
#include <libsigrok/libsigrok.h>
#include "libsigrok-internal.h"
return SR_OK;
}
+/**
+ * Scale a float value to the appropriate SI prefix.
+ *
+ * @param[in,out] value The float value to convert to appropriate SI prefix.
+ * @param[in,out] digits The number of significant decimal digits in value.
+ *
+ * @return The SI prefix to which value was scaled, as a printable string.
+ *
+ * @since 0.5.0
+ */
+SR_API const char *sr_analog_si_prefix(float *value, int *digits)
+{
+#define NEG_PREFIX_COUNT 5 /* number of prefixes below unity */
+#define POS_PREFIX_COUNT (int)(ARRAY_SIZE(prefixes) - NEG_PREFIX_COUNT - 1)
+ static const char *prefixes[] = { "f","p","n","ยต","m","","k","M","G","T" };
+
+ if (value == NULL || digits == NULL || isnan(*value))
+ return prefixes[NEG_PREFIX_COUNT];
+
+ float logval = log10f(fabsf(*value));
+ int prefix = (logval / 3) - (logval < 1);
+
+ if (prefix < -NEG_PREFIX_COUNT) prefix = -NEG_PREFIX_COUNT;
+ if (3 * prefix < -*digits) prefix = (-*digits + 2 * (*digits < 0)) / 3;
+ if (prefix > POS_PREFIX_COUNT) prefix = POS_PREFIX_COUNT;
+
+ *value *= powf(10, -3 * prefix);
+ *digits += 3 * prefix;
+ return prefixes[prefix + NEG_PREFIX_COUNT];
+}
+
/**
* Convert the unit/MQ/MQ flags in the analog struct to a string.
*