always cancel down fractions (frac_t) to avoid overflows and playback

problems (e.g. when using resample and equalizer filters together, see
http://mplayerhq.hu/pipermail/mplayer-users/2004-December/050058.html)


git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@14434 b3059339-0415-0410-9bf9-f77b7e298cf2

1 files changed, 46 insertions, 6 deletions

diff --git a/libaf/af.c b/libaf/af.c
index 2165eb3baf..fa5963144f 100644
--- a/libaf/af.c
+++ b/libaf/af.c
@@ -524,8 +524,7 @@ int af_outputlen(af_stream_t* s, int len)
   register frac_t mul = {1,1};
   // Iterate through all filters 
   do{
-    mul.n *= af->mul.n;
-    mul.d *= af->mul.d;
+    af_frac_mul(&mul, &af->mul);
     af=af->next;
   }while(af);
   return t * (((len/t)*mul.n + 1)/mul.d);
@@ -542,8 +541,7 @@ int af_inputlen(af_stream_t* s, int len)
   register frac_t mul = {1,1};
   // Iterate through all filters 
   do{
-    mul.n *= af->mul.n;
-    mul.d *= af->mul.d;
+    af_frac_mul(&mul, &af->mul);
     af=af->next;
   }while(af);
   return t * (((len/t) * mul.d - 1)/mul.n);
@@ -567,8 +565,7 @@ int af_calc_insize_constrained(af_stream_t* s, int len,
   register frac_t mul = {1,1};
   // Iterate through all filters and calculate total multiplication factor
   do{
-    mul.n *= af->mul.n;
-    mul.d *= af->mul.d;
+    af_frac_mul(&mul, &af->mul);
     af=af->next;
   }while(af);
   // Sanity check 
@@ -645,6 +642,49 @@ af_instance_t *af_control_any_rev (af_stream_t* s, int cmd, void* arg) {
   return NULL;
 }
 
+/**
+ * \brief calculate greatest common divisior of a and b.
+ *   Extended for negative and 0 values. If both are 0 the result is 1.
+ *   The sign of the result will be so that it has the same sign as b.
+ */
+int af_gcd(register int a, register int b) {
+  int b_org = b;
+  while (b != 0) {
+    a %= b;
+    if (a == 0)
+      break;
+    b %= a;
+  }
+  // the result is either in a or b. As the other one is 0 just add them.
+  a += b;
+  if (!a)
+    return 1;
+  if (a * b_org < 0)
+    return -a;
+  return a;
+}
+
+/**
+ * \brief cancel down a fraction f
+ */
+void af_frac_cancel(frac_t *f) {
+  int gcd = af_gcd(f->n, f->d);
+  f->n /= gcd;
+  f->d /= gcd;
+}
+
+/**
+ * \brief multiply out by in and store result in out.
+ *        the resulting fraction wil be cancelled down
+ *        if in and out were.
+ */
+void af_frac_mul(frac_t *out, const frac_t *in) {
+  int gcd1 = af_gcd(out->n, in->d);
+  int gcd2 = af_gcd(in->n, out->d);
+  out->n = (out->n / gcd1) * (in->n / gcd2);
+  out->d = (out->d / gcd2) * (in->d / gcd1);
+}
+
 void af_help (void) {
   int i = 0;
   af_msg(AF_MSG_INFO, "Available audio filters:\n");