aacpsy: use exp2(f) instead of pow(f)(2,...)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/aacpsy.c

@@ -24,6 +24,8 @@
  * AAC encoder psychoacoustic model
  */
 
+#include "libavutil/libm.h"
+
 #include "avcodec.h"
 #include "aactab.h"
 #include "psymodel.h"
@@ -333,7 +335,7 @@ static av_cold int psy_3gpp_init(FFPsyContext *ctx) {
             coeff->spread_low[1] = pow(10.0, -bark_width * en_spread_low);
             coeff->spread_hi [1] = pow(10.0, -bark_width * en_spread_hi);
             pe_min = bark_pe * bark_width;
-            minsnr = pow(2.0f, pe_min / band_sizes[g]) - 1.5f;
+            minsnr = exp2(pe_min / band_sizes[g]) - 1.5f;
             coeff->min_snr = av_clipf(1.0f / minsnr, PSY_SNR_25DB, PSY_SNR_1DB);
         }
         start = 0;
@@ -524,8 +526,8 @@ static float calc_reduction_3gpp(float a, float desired_pe, float pe,
 {
     float thr_avg, reduction;
 
-    thr_avg   = powf(2.0f, (a - pe) / (4.0f * active_lines));
-    reduction = powf(2.0f, (a - desired_pe) / (4.0f * active_lines)) - thr_avg;
+    thr_avg   = exp2f((a - pe) / (4.0f * active_lines));
+    reduction = exp2f((a - desired_pe) / (4.0f * active_lines)) - thr_avg;
 
     return FFMAX(reduction, 0.0f);
 }
@@ -703,7 +705,7 @@ static void psy_3gpp_analyze_channel(FFPsyContext *ctx, int channel,
                         float delta_sfb_pe = band->norm_fac * norm_fac * delta_pe;
                         float thr = band->thr;
 
-                        thr *= powf(2.0f, delta_sfb_pe / band->active_lines);
+                        thr *= exp2f(delta_sfb_pe / band->active_lines);
                         if (thr > coeffs[g].min_snr * band->energy && band->avoid_holes == PSY_3GPP_AH_INACTIVE)
                             thr = FFMAX(band->thr, coeffs[g].min_snr * band->energy);
                         band->thr = thr;