shithub: sox

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make this function available generally

--- a/src/effects_i.c

+++ b/src/effects_i.c

@@ -207,6 +207,47 @@

     return NULL;

 }

+/* a note is given as an int,

+ * 0   => 440 Hz = A

+ * >0  => number of half notes 'up',

+ * <0  => number of half notes down,

+ * example 12 => A of next octave, 880Hz

+ *

+ * calculated by freq = 440Hz * 2**(note/12)

+ */

+static double calc_note_freq(double note)

+{

+  return 440.0 * pow(2.0, note / 12.0);

+}

+

+/* Read string 'text' and convert to frequency.

+ * 'text' can be a positive number which is the frequency in Hz.

+ * If 'text' starts with a hash '%' and a following number the corresponding

+ * note is calculated.

+ * Return -1 on error.

+ */

+double lsx_parse_frequency(char const * text, char * * end_ptr)

+{

+  double result;

+

+  if (*text == '%') {

+    result = strtod(text + 1, end_ptr);

+    if (*end_ptr == text + 1)

+      return -1;

+    return calc_note_freq(result);

+  }

+  result = strtod(text, end_ptr);

+  if (end_ptr) {

+    if (*end_ptr == text)

+      return -1;

+    if (**end_ptr == 'k') {

+      result *= 1000;

+      ++*end_ptr;

+    }

+  }

+  return result < 0 ? -1 : result;

+}

+

 double bessel_I_0(double x)

 {

   double term = 1, sum = 1, last_sum, x2 = x / 2;

--- a/src/sox_i.h

+++ b/src/sox_i.h

@@ -44,6 +44,7 @@

     double max,         /* Maximum value on the y-axis. (e.g. +1) */

     double phase);      /* Phase at 1st point; 0..2pi. (e.g. pi/2 for cosine) */

 char const * lsx_parsesamples(sox_rate_t rate, const char *str, sox_size_t *samples, int def);

+double lsx_parse_frequency(char const * text, char * * end_ptr);

 sox_sample_t lsx_gcd(sox_sample_t a, sox_sample_t b);

 sox_sample_t lsx_lcm(sox_sample_t a, sox_sample_t b);