Fix an issue where dsp.c would interpret multiple dtmf events from a single key press.

When receiving calls from a mobile phone into a DISA system on a connection with
significant interference, the reporter's Asterisk system would interpret DTMF incorrectly
and replicate digits received. This patch resolves that by increasing the number of
frames a mismatch has to be detected before assuming the DTMF is over by 1 frame and
adjusts dtmf_detect function to reset hits and misses only when an edge is detected.

(closes issue ASTERISK-17493)
Reported by: Alec Davis
Patches:
	bug18904-refactor.diff.txt uploaded by Alec Davis (license 5546)
Review: https://reviewboard.asterisk.org/r/1130/
........

Merged revisions 349728 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 349729 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@349730 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/dsp.c

@@ -201,9 +201,9 @@ enum gsamp_thresh {
 #define DTMF_GSIZE		102
 
 /* How many successive hits needed to consider begin of a digit */
-#define DTMF_HITS_TO_BEGIN	2
+#define DTMF_HITS_TO_BEGIN	4
 /* How many successive misses needed to consider end of a digit */
-#define DTMF_MISSES_TO_END	3
+#define DTMF_MISSES_TO_END	4
 
 /*!
  * \brief The default silence threshold we will use if an alternate
@@ -721,41 +721,40 @@ static int dtmf_detect(struct ast_dsp *dsp, digit_detect_state_t *s, int16_t amp
 			}
 		}
 
+		if (hit == s->td.dtmf.lasthit) {
 			if (s->td.dtmf.current_hit) {
 				/* We are in the middle of a digit already */
+				if (hit) {
 					if (hit != s->td.dtmf.current_hit) {
-				s->td.dtmf.misses++;
-				if (s->td.dtmf.misses == s->td.dtmf.misses_to_end) {
-					/* There were enough misses to consider digit ended */
+						/* Look for a start of a new digit.
+						   This is because hits_to_begin may be smaller than misses_to_end
+						   and we may find the beginning of new digit before we consider last one ended. */
 						s->td.dtmf.current_hit = 0;
-				}
 					} else {
-				s->td.dtmf.misses = 0;
 						/* Current hit was same as last, so increment digit duration (of last digit) */
 						s->digitlen[s->current_digits - 1] += DTMF_GSIZE;
 					}
-		}
-
-		/* Look for a start of a new digit no matter if we are already in the middle of some
-		   digit or not. This is because hits_to_begin may be smaller than misses_to_end
-		   and we may find begin of new digit before we consider last one ended. */
-		if (hit) {
-			if (hit == s->td.dtmf.lasthit) {
-				s->td.dtmf.hits++;
 				} else {
-				s->td.dtmf.hits = 1;
+					/* No Digit */
+					s->td.dtmf.misses++;
+					if (s->td.dtmf.misses == s->td.dtmf.misses_to_end) {
+						/* There were enough misses to consider digit ended */
+						s->td.dtmf.current_hit = 0;
 					}
-
-			if (s->td.dtmf.hits == s->td.dtmf.hits_to_begin && hit != s->td.dtmf.current_hit) {
+				}
+			} else if (hit) {
+				/* Detecting new digit */
+				s->td.dtmf.hits++;
+				if (s->td.dtmf.hits == s->td.dtmf.hits_to_begin) {
 					store_digit(s, hit);
 					s->td.dtmf.current_hit = hit;
-				s->td.dtmf.misses = 0;
 				}
-		} else {
-			s->td.dtmf.hits = 0;
 			}
-
+		} else {
+			s->td.dtmf.hits = 1;
+			s->td.dtmf.misses = 1;
 			s->td.dtmf.lasthit = hit;
+		}
 
 		/* If we had a hit in this block, include it into mute fragment */
 		if (squelch && hit) {