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trim: use lsx_parseposition

Use the new lsx_parseposition function for the trim effect, removing much
of the dedicated parsing as it is now handled by lsx_parseposition. Update
documentation.

--- a/sox.1

+++ b/sox.1

@@ -3969,20 +3969,12 @@

 .I depth

 (default 40).

 .TP

-\fBtrim\fR {[\fB=\fR\^|\^\fB\-\fR]\fIposition\fR}

+\fBtrim\fR {\fIposition(+)\fR}

 Cuts portions out of the audio.  Any number of \fIposition\fRs may be

 given; audio is not sent to the output until the first \fIposition\fR

 is reached.  The effect then alternates between copying and discarding

-audio at each \fIposition\fR.

-.SP

-If a \fIposition\fR is preceded by an equals or minus sign, it is

-interpreted relative to the beginning or the end of the audio,

-respectively.  (The audio length must be known for end-relative

-locations to work.)  Otherwise, it is considered an offset from the

-last \fIposition\fR, or from the start of audio for the first

-parameter.  Using a value of 0 for the first \fIposition\fR

+audio at each \fIposition\fR.  Using a value of 0 for the first \fIposition\fR

 parameter allows copying from the beginning of the audio.

-Any time specification may be used for \fIposition\fR.

 .SP

 For example,

 .EX

@@ -3992,7 +3984,11 @@

 .EX

    play infile trim 12:34 =15:00 -2:00

 .EE

-will play from 12 minutes 34 seconds into the audio up to 15 minutes into

+and

+.EX

+   play infile trim 12:34 2:26 -2:00

+.EE

+will both play from 12 minutes 34 seconds into the audio up to 15 minutes into

 the audio (i.e. 2 minutes and 26 seconds long), then resume playing two

 minutes before the end of audio.

 .TP

--- a/src/trim.c

+++ b/src/trim.c

@@ -28,15 +28,11 @@

   struct {

     uint64_t sample; /* NB: wide samples */

     char *argstr;

-    enum {

-      a_start, a_latest, a_end

-    } anchor;

   } *pos;

   /* state */

   unsigned int current_pos;

   uint64_t samples_read; /* NB: wide samples */

   sox_bool copying;

-  sox_bool uses_end;

 } priv_t;

 static int parse(sox_effect_t *effp, int argc, char **argv)

@@ -46,24 +42,15 @@

   --argc, ++argv;

   p->num_pos = argc;

   lsx_Calloc(p->pos, p->num_pos);

-  p->uses_end = sox_false;

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

-    uint64_t dummy;

     const char *arg = argv[i];

-    if (arg[0] == '=') {

-      p->pos[i].anchor = a_start;

-      arg++;

-    } else if (arg[0] == '-') {

-      p->pos[i].anchor = a_end;

-      p->uses_end = sox_true;

-      arg++;

-    } else

-      p->pos[i].anchor = a_latest;

     p->pos[i].argstr = lsx_strdup(arg);

     /* dummy parse to check for syntax errors */

-    arg = lsx_parsesamples(0., arg, &dummy, 't');

-    if (!arg || *arg)

+    arg = lsx_parseposition(0., arg, NULL, (uint64_t)0, (uint64_t)0, '+');

+    if (!arg || *arg) {

+      lsx_fail("Error parsing position %u", i+1);

       return lsx_usage(effp);

+    }

   }

   return SOX_SUCCESS;

 }

@@ -80,28 +67,13 @@

   p->copying = sox_false;

   /* calculate absolute positions */

-  if (in_length == SOX_UNKNOWN_LEN && p->uses_end) {

-    lsx_fail("Can't use positions relative to end: audio length is unknown.");

-    return SOX_EOF;

-  }

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

-    uint64_t s, res = 0;

-    if (!lsx_parsesamples(effp->in_signal.rate, p->pos[i].argstr, &s, 't'))

-      return lsx_usage(effp);

-    switch (p->pos[i].anchor) {

-      case a_start: res = s; break;

-      case a_latest: res = last_seen + s; break;

-      case a_end:

-        if (s <= in_length)

-          res = in_length - s;

-        else {

-          lsx_fail("Position %u is before start of audio.", i+1);

-          return SOX_EOF;

-        }

-        break;

+    if (!lsx_parseposition(effp->in_signal.rate, p->pos[i].argstr, &p->pos[i].sample, last_seen, in_length, '+')) {

+      lsx_fail("Position %u is relative to end of audio, but audio length is unknown", i+1);

+      return SOX_EOF;

     }

-    last_seen = p->pos[i].sample = res;

-    lsx_debug_more("position %u at %" PRIu64, i+1, res);

+    last_seen = p->pos[i].sample;

+    lsx_debug_more("position %u at %" PRIu64, i+1, last_seen);

   }

   /* sanity checks */

@@ -119,6 +91,13 @@

       lsx_warn("%s position is after expected end of audio.",

           p->pos[0].sample > in_length ? "Start" : "End");

+  /* avoid unnecessary work */

+  if (in_length == SOX_UNKNOWN_LEN)

+    while (p->num_pos && p->pos[p->num_pos-1].sample == SOX_UNKNOWN_LEN) {

+      lsx_debug_more("removing `-0' position");

+      p->num_pos--;

+      free(p->pos[p->num_pos].argstr);

+    }

   if (p->num_pos == 1 && !p->pos[0].sample)

     return SOX_EFF_NULL;

@@ -207,7 +186,7 @@

 sox_effect_handler_t const *lsx_trim_effect_fn(void)

 {

   static sox_effect_handler_t handler = {

-    "trim", "{[=|-]position}",

+    "trim", "{position}",

     SOX_EFF_MCHAN | SOX_EFF_LENGTH | SOX_EFF_MODIFY,

     parse, start, flow, drain, NULL, lsx_kill,

     sizeof(priv_t)