strutil: add text to float conversion which also gets precision from text

[libsigrok.git] / src / strutil.c

diff --git a/src/strutil.c b/src/strutil.c
index 0dff3c4b48c0bf8df4014f73bddde9dd279644c3..6ed2b85dcea244059aa4d4d97a40999302f3145d 100644 (file)
--- a/src/strutil.c
+++ b/src/strutil.c
@@ -272,6 +272,77 @@ SR_PRIV int sr_atod_ascii(const char *str, double *ret)
        return SR_OK;
 }
 
+/**
+ * Convert text to a floating point value, and get its precision.
+ *
+ * @param[in] str The input text to convert.
+ * @param[out] ret The conversion result, a double precision float number.
+ * @param[out] digits The number of significant decimals.
+ *
+ * @returns SR_OK in case of successful text to number conversion.
+ * @returns SR_ERR when conversion fails.
+ *
+ * @since 0.6.0
+ */
+SR_PRIV int sr_atod_ascii_digits(const char *str, double *ret, int *digits)
+{
+       const char *p;
+       int *dig_ref, m_dig, exp;
+       char c;
+       double f;
+
+       /*
+        * Convert floating point text to the number value, _and_ get
+        * the value's precision in the process. Steps taken to do it:
+        * - Skip leading whitespace.
+        * - Count the number of decimals after the mantissa's period.
+        * - Get the exponent's signed value.
+        *
+        * This implementation still uses common code for the actual
+        * conversion, but "violates API layers" by duplicating the
+        * text scan, to get the number of significant digits.
+        */
+       p = str;
+       while (*p && isspace(*p))
+               p++;
+       if (*p == '-' || *p == '+')
+               p++;
+       m_dig = 0;
+       exp = 0;
+       dig_ref = NULL;
+       while (*p) {
+               c = *p++;
+               if (toupper(c) == 'E') {
+                       exp = strtol(p, NULL, 10);
+                       break;
+               }
+               if (c == '.') {
+                       m_dig = 0;
+                       dig_ref = &m_dig;
+                       continue;
+               }
+               if (isdigit(c)) {
+                       if (dig_ref)
+                               (*dig_ref)++;
+                       continue;
+               }
+               /* Need not warn, conversion will fail. */
+               break;
+       }
+       sr_spew("atod digits: txt \"%s\" -> m %d, e %d -> digits %d",
+               str, m_dig, exp, m_dig + -exp);
+       m_dig += -exp;
+
+       if (sr_atod_ascii(str, &f) != SR_OK)
+               return SR_ERR;
+       if (ret)
+               *ret = f;
+       if (digits)
+               *digits = m_dig;
+
+       return SR_OK;
+}
+
 /**
  * Convert a string representation of a numeric value to a float. The
  * conversion is strict and will fail if the complete string does not represent