#187 Square (U parabola) fade

[Guido Aulisi]

Hi,
this patch adds a square fade (U parabola) to the fade effect.
I like it very much when fading out songs (30 seconds fade).

diff --git a/src/fade.c b/src/fade.c
index 3cf4876..04ebfd7 100644
--- a/src/fade.c
+++ b/src/fade.c
@@ -19,6 +19,7 @@
                                 * in given time. */
 #define FADE_TRI        't'     /* Linear slope. */
 #define FADE_PAR        'p'     /* Inverted parabola. */
+#define FADE_SQUARE     's'     /* Square. */

 #include <string.h>

@@ -58,7 +59,7 @@ static int sox_fade_getopts(sox_effect_t * effp, int argc, char **argv)
      * string off for later computations.
      */

-    if (sscanf(argv[0], "%1[qhltp]", t_char))
+    if (sscanf(argv[0], "%1[qhltps]", t_char))
     {
         fade->in_fadetype = *t_char;
         fade->out_fadetype = *t_char;
@@ -370,6 +371,10 @@ static double fade_gain(uint64_t index, uint64_t range, int type)
       retval = (1 - (1 - findex)  * (1 - findex));
       break;

+    case FADE_SQUARE :             /* square */
+      retval = findex * findex;
+      break;
+
     /* TODO: more fade curves? */
     default :                  /* Error indicating wrong fade curve */
       retval = -1.0;