Replace pow(x, 0.75) with sqrtf(x * sqrtf(x)) for a 33% speedup.

Originally committed as revision 19459 to svn://svn.ffmpeg.org/ffmpeg/trunk

Alex Converse committed 17 years ago

Commit 3d51be01 parent 4e67aed1 file · +8 −5Browse files

Showing the changes to libavcodec/aaccoder.c (1 of 1 file). Show all

Unified · Split

  */
 static av_always_inline int quant(float coef, const float Q)
 {
-    return pow(coef * Q, 0.75) + 0.4054;
+    float a = coef * Q;
+    return sqrtf(a * sqrtf(a)) + 0.4054;
 }
 static void quantize_bands(int (*out)[2], const float *in, const float *scaled,
 {
 #ifndef USE_REALLY_FULL_SEARCH
     int i;
-    for (i = 0; i < size; i++)
+    for (i = 0; i < size; i++) {
-        out[i] = pow(fabsf(in[i]), 0.75);
+        float a = fabsf(in[i]);
+        out[i] = sqrtf(a * sqrtf(a));
+    }
 #endif /* USE_REALLY_FULL_SEARCH */
 }
     const int dim = cb < FIRST_PAIR_BT ? 4 : 2;
     int resbits = 0;
 #ifndef USE_REALLY_FULL_SEARCH
-    const float  Q34 = pow(Q, 0.75);
+    const float  Q34 = sqrtf(Q * sqrtf(Q));
     const int range  = aac_cb_range[cb];
     const int maxval = aac_cb_maxval[cb];
     int offs[4];
     const int dim = (cb < FIRST_PAIR_BT) ? 4 : 2;
     int i, j, k;
 #ifndef USE_REALLY_FULL_SEARCH
-    const float  Q34 = pow(Q, 0.75);
+    const float  Q34 = sqrtf(Q * sqrtf(Q));
     const int range  = aac_cb_range[cb];
     const int maxval = aac_cb_maxval[cb];
     int offs[4];

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