af_biquad: unroll loop, remove variable copies

This makes the code about 7% faster
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/af_biquads.c

@@ -182,7 +182,32 @@ static void biquad_## name (const void *input, void *output, int len,         \
     double o2 = *out2;                                                        \
     int i;                                                                    \
                                                                               \
-    for (i = 0; i < len; i++) {                                               \
+    for (i = 0; i+1 < len; i++) {                                             \
+        o2 = i2 * b2 + i1 * b1 + ibuf[i] * b0 - o2 * a2 - o1 * a1;            \
+        i2 = ibuf[i];                                                         \
+        if (o2 < min) {                                                       \
+            av_log(NULL, AV_LOG_WARNING, "clipping\n");                       \
+            obuf[i] = min;                                                    \
+        } else if (o2 > max) {                                                \
+            av_log(NULL, AV_LOG_WARNING, "clipping\n");                       \
+            obuf[i] = max;                                                    \
+        } else {                                                              \
+            obuf[i] = o2;                                                     \
+        }                                                                     \
+        i++;                                                                  \
+        o1 = i1 * b2 + i2 * b1 + ibuf[i] * b0 - o1 * a2 - o2 * a1;            \
+        i1 = ibuf[i];                                                         \
+        if (o1 < min) {                                                       \
+            av_log(NULL, AV_LOG_WARNING, "clipping\n");                       \
+            obuf[i] = min;                                                    \
+        } else if (o1 > max) {                                                \
+            av_log(NULL, AV_LOG_WARNING, "clipping\n");                       \
+            obuf[i] = max;                                                    \
+        } else {                                                              \
+            obuf[i] = o1;                                                     \
+        }                                                                     \
+    }                                                                         \
+    if (i < len) {                                                            \
         double o0 = ibuf[i] * b0 + i1 * b1 + i2 * b2 - o1 * a1 - o2 * a2;     \
         i2 = i1;                                                              \
         i1 = ibuf[i];                                                         \