timefilter: better selftest code.

Add support for divergence detection and variable period.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavdevice/timefilter.c

@@ -89,6 +89,7 @@ int main(void)
 #define SAMPLES 1000
     double ideal[SAMPLES];
     double samples[SAMPLES];
+    double samplet[SAMPLES];
 #if 1
     for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
         for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
@@ -100,13 +101,16 @@ int main(void)
 #endif
             double best_error = 1000000000;
             double bestpar0   = 1;
-            double bestpar1   = 0.001;
+            double bestpar1   = 1;
             int better, i;
 
             av_lfg_init(&prng, 123);
             for (i = 0; i < SAMPLES; i++) {
-                ideal[i]   = 10 + i + n1 * i / (1000);
+                samplet[i] = 10 + i + (av_lfg_get(&prng) < LFG_MAX/2 ? 0 : 0.999);
+                ideal[i]   = samplet[i] + n1 * i / (1000);
                 samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
+                if(i && samples[i]<samples[i-1])
+                    samples[i]=samples[i-1]+0.001;
             }
 
             do {
@@ -118,7 +122,9 @@ int main(void)
                         TimeFilter *tf = ff_timefilter_new(1, par0, par1);
                         for (i = 0; i < SAMPLES; i++) {
                             double filtered;
-                            filtered = ff_timefilter_update(tf, samples[i], 1);
+                            filtered = ff_timefilter_update(tf, samples[i], i ? (samplet[i] - samplet[i-1]) : 1);
+                            if(filtered < 0 || filtered > 1000000000)
+                                printf("filter is unstable\n");
                             error   += (filtered - ideal[i]) * (filtered - ideal[i]);
                         }
                         ff_timefilter_destroy(tf);