[FFmpeg-soc] [soc]: r4945 - amr/amrnbdec.c

[cmcq]

Author: cmcq
Date: Wed Aug  5 14:50:55 2009
New Revision: 4945

Log:
sqrt is faster than log by about five times (or 2.5 times with libimf)
test program:

#include <stdio.h>
#include <math.h>
#include <float.h>

int main(int argc, char *argv[])
{
    float x;
    float y = 0;
    if (argc == 1) {
        for (x = 1; x < 10; x += 0.0000005)
            y += log10f(x);
        printf("Total log: %f\n", y);
    } else {
        for (x = 1; x < 8; x += 0.0000005)
            y += sqrtf(x);
        printf("Total sqrt: %f\n", y);
    }
    return 0;
}

$ time ./test 1; time ./test
Total sqrt: 30237319.627204

real	0m0.249s
user	0m0.248s
sys	0m0.000s
Total log: 11628338.000000

real	0m1.385s
user	0m1.372s
sys	0m0.008s

Modified:
   amr/amrnbdec.c

Modified: amr/amrnbdec.c
==============================================================================
--- amr/amrnbdec.c	Wed Aug  5 14:32:43 2009	(r4944)
+++ amr/amrnbdec.c	Wed Aug  5 14:50:55 2009	(r4945)
@@ -700,11 +700,11 @@ static float fixed_gain_prediction(float
 
     energy_pred = ff_dot_productf(energy_pred_fac, prev_pred_error, 4);
 
-    energy_fixed_mean = ff_energyf(fixed_vector, AMR_SUBFRAME_SIZE);
-    energy_fixed_mean = 10.0 * log10f(energy_fixed_mean / AMR_SUBFRAME_SIZE);
+    energy_fixed_mean = sqrt(ff_energyf(fixed_vector, AMR_SUBFRAME_SIZE) /
+                             AMR_SUBFRAME_SIZE);
 
-    return powf(10.0, 0.05 * (energy_pred + energy_mean[mode] -
-                              energy_fixed_mean));
+    return powf(10.0, 0.05 * (energy_pred + energy_mean[mode])) /
+        energy_fixed_mean;
 }
 
 /**