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bend: use lsx_parseposition

Use the new lsx_parseposition function for the bend effect and update
the documentation accordingly.

--- a/sox.1

+++ b/sox.1

@@ -1627,16 +1627,13 @@

 .SP

 See also \fBequalizer\fR for a peaking equalisation effect.

 .TP

-\fBbend\fR [\fB\-f \fIframe-rate\fR(25)] [\fB\-o \fIover-sample\fR(16)] { \fIdelay\fB,\fIcents\fB,\fIduration\fR }

+\fBbend\fR [\fB\-f \fIframe-rate\fR(25)] [\fB\-o \fIover-sample\fR(16)] { \fIstart-position(+)\fB,\fIcents\fB,\fIend-position(+)\fR }

 Changes pitch by specified amounts at specified times.

-Each given triple: \fIdelay\fB,\fIcents\fB,\fIduration\fR specifies one bend.

-.I delay

-is the amount of time after the start of the audio stream, or the end of the previous bend, at which to start bending the pitch;

-.I cents

-is the number of cents (100 cents = 1 semitone) by which to bend the pitch, and

-.I duration

-the length of time over which the pitch will be bent.  For \fIdelay\fR and

-\fIduration\fR, any time specification may be used.

+Each given triple: \fIstart-position\fB,\fIcents\fB,\fIend-position\fR

+specifies one bend.

+\fIcents\fR is the number of cents (100 cents = 1 semitone) by which to

+bend the pitch. The other values specify the points in time at which to start

+and end bending the pitch, respectively.

 .SP

 The pitch-bending algorithm utilises the Discrete Fourier Transform (DFT)

 at a particular frame rate and over-sampling rate.

@@ -1654,6 +1651,8 @@

    play \-n synth 2.5 sin 667 gain 1 \\

 	bend .35,180,.25  .15,740,.53  0,\-520,.3

 .EE

+Here, the first bend runs from 0.35 to 0.6, and the second one from 0.75

+to 1.28 seconds.

 Note that the clipping that is produced in this example is deliberate;

 to remove it, use

 .B gain\ \-5

--- a/src/bend.c

+++ b/src/bend.c

@@ -70,23 +70,43 @@

 {

   priv_t *p = (priv_t *) effp->priv;

   size_t i;

-  uint64_t time = 0, delay;

   char const *next;

+  uint64_t last_seen = 0;

+  const uint64_t in_length = argv ? 0 :

+    (effp->in_signal.length != SOX_UNKNOWN_LEN ?

+     effp->in_signal.length / effp->in_signal.channels : SOX_UNKNOWN_LEN);

   for (i = 0; i < p->nbends; ++i) {

     if (argv)   /* 1st parse only */

       p->bends[i].str = lsx_strdup(argv[i]);

-    next = lsx_parsesamples(rate, p->bends[i].str, &delay, 't');

+

+    next = lsx_parseposition(rate, p->bends[i].str,

+             argv ? NULL : &p->bends[i].start, last_seen, in_length, '+');

+    last_seen = p->bends[i].start;

     if (next == NULL || *next != ',')

       break;

-    p->bends[i].start = time += delay;

+

     p->bends[i].cents = strtod(next + 1, (char **)&next);

     if (p->bends[i].cents == 0 || *next != ',')

       break;

-    next = lsx_parsesamples(rate, next + 1, &p->bends[i].duration, 't');

+

+    next = lsx_parseposition(rate, next + 1,

+             argv ? NULL : &p->bends[i].duration, last_seen, in_length, '+');

+    last_seen = p->bends[i].duration;

     if (next == NULL || *next != '\0')

       break;

-    time += p->bends[i].duration;

+

+    /* sanity checks */

+    if (!argv && p->bends[i].duration < p->bends[i].start) {

+      lsx_fail("Bend %" PRIuPTR " has negative width", i+1);

+      break;

+    }

+    if (!argv && i && p->bends[i].start < p->bends[i-1].start) {

+      lsx_fail("Bend %" PRIuPTR " overlaps with previous one", i+1);

+      break;

+    }

+

+    p->bends[i].duration -= p->bends[i].start;

   }

   if (i < p->nbends)

     return lsx_usage(effp);

@@ -298,7 +318,7 @@

 sox_effect_handler_t const *lsx_bend_effect_fn(void)

 {

   static sox_effect_handler_t handler = {

-    "bend", "[-f frame-rate(25)] [-o over-sample(16)] {delay,cents,duration}",

+    "bend", "[-f frame-rate(25)] [-o over-sample(16)] {start,cents,end}",

     0, create, start, flow, 0, stop, lsx_kill, sizeof(priv_t)

   };

   return &handler;