[FFmpeg-cvslog] aacenc: use the decoder's lcg PRNG

[Rostislav Pehlivanov]

ffmpeg | branch: master | Rostislav Pehlivanov <atomnuker at gmail.com> | Sat Oct  8 01:47:04 2016 +0100| [230178dfe25ebe27934062c9fa8e2a40e6ad2b0b] | committer: Rostislav Pehlivanov

aacenc: use the decoder's lcg PRNG

Using lfg was an overkill in this case where the random numbers
were only used for encoder descisions. Should increase result
uniformity between different FPUs and gives a slight speedup.

Signed-off-by: Rostislav Pehlivanov <atomnuker at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=230178dfe25ebe27934062c9fa8e2a40e6ad2b0b
---

 libavcodec/aaccoder.c     |  8 +++-----
 libavcodec/aacenc.c       |  2 +-
 libavcodec/aacenc.h       |  2 --
 libavcodec/aacenc_utils.h | 13 +++++++++++++
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 284b401..35787e8 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -643,11 +643,9 @@ static void search_for_pns(AACEncContext *s, AVCodecContext *avctx, SingleChanne
                 float band_energy, scale, pns_senergy;
                 const int start_c = (w+w2)*128+sce->ics.swb_offset[g];
                 band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
-                for (i = 0; i < sce->ics.swb_sizes[g]; i+=2) {
-                    double rnd[2];
-                    av_bmg_get(&s->lfg, rnd);
-                    PNS[i+0] = (float)rnd[0];
-                    PNS[i+1] = (float)rnd[1];
+                for (i = 0; i < sce->ics.swb_sizes[g]; i++) {
+                    s->random_state  = lcg_random(s->random_state);
+                    PNS[i] = s->random_state;
                 }
                 band_energy = s->fdsp->scalarproduct_float(PNS, PNS, sce->ics.swb_sizes[g]);
                 scale = noise_amp/sqrtf(band_energy);
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index 9e421a9..ee3cbf8 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -1031,7 +1031,7 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
         goto fail;
     s->psypp = ff_psy_preprocess_init(avctx);
     ff_lpc_init(&s->lpc, 2*avctx->frame_size, TNS_MAX_ORDER, FF_LPC_TYPE_LEVINSON);
-    av_lfg_init(&s->lfg, 0x72adca55);
+    s->random_state = 0x1f2e3d4c;
 
     if (HAVE_MIPSDSP)
         ff_aac_coder_init_mips(s);
diff --git a/libavcodec/aacenc.h b/libavcodec/aacenc.h
index 63e7893..1ace00d 100644
--- a/libavcodec/aacenc.h
+++ b/libavcodec/aacenc.h
@@ -23,7 +23,6 @@
 #define AVCODEC_AACENC_H
 
 #include "libavutil/float_dsp.h"
-#include "libavutil/lfg.h"
 #include "avcodec.h"
 #include "put_bits.h"
 
@@ -100,7 +99,6 @@ typedef struct AACEncContext {
     FFTContext mdct1024;                         ///< long (1024 samples) frame transform context
     FFTContext mdct128;                          ///< short (128 samples) frame transform context
     AVFloatDSPContext *fdsp;
-    AVLFG lfg;                                   ///< PRNG needed for PNS
     float *planar_samples[8];                    ///< saved preprocessed input
 
     int profile;                                 ///< copied from avctx
diff --git a/libavcodec/aacenc_utils.h b/libavcodec/aacenc_utils.h
index bb1dcb4..ff9188a 100644
--- a/libavcodec/aacenc_utils.h
+++ b/libavcodec/aacenc_utils.h
@@ -252,6 +252,19 @@ static inline int ff_sfdelta_can_replace(const SingleChannelElement *sce,
         && sce->sf_idx[nextband[band]] <= (new_sf + SCALE_MAX_DIFF);
 }
 
+/**
+ * linear congruential pseudorandom number generator
+ *
+ * @param   previous_val    pointer to the current state of the generator
+ *
+ * @return  Returns a 32-bit pseudorandom integer
+ */
+static av_always_inline int lcg_random(unsigned previous_val)
+{
+    union { unsigned u; int s; } v = { previous_val * 1664525u + 1013904223 };
+    return v.s;
+}
+
 #define ERROR_IF(cond, ...) \
     if (cond) { \
         av_log(avctx, AV_LOG_ERROR, __VA_ARGS__); \