use LFG instead of Mersenne Twister for AC-3 PRNG

Originally committed as revision 14815 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -33,7 +33,6 @@
 #include <string.h>
 
 #include "libavutil/crc.h"
-#include "libavutil/random.h"
 #include "avcodec.h"
 #include "ac3_parser.h"
 #include "bitstream.h"
@@ -198,7 +197,7 @@ static av_cold int ac3_decode_init(AVCodecContext *avctx)
     ff_mdct_init(&s->imdct_512, 9, 1);
     ff_kbd_window_init(s->window, 5.0, 256);
     dsputil_init(&s->dsp, avctx);
-    av_init_random(0, &s->dith_state);
+    av_lfg_init(&s->dith_state, 0);
 
     /* set bias values for float to int16 conversion */
     if(s->dsp.float_to_int16_interleave == ff_float_to_int16_interleave_c) {
@@ -450,7 +449,7 @@ static void get_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_grou
         tbap = bap[i];
         switch (tbap) {
             case 0:
-                coeffs[i] = (av_random(&s->dith_state) & 0x7FFFFF) - 0x400000;
+                coeffs[i] = (av_lfg_get(&s->dith_state) & 0x7FFFFF) - 0x400000;
                 break;
 
             case 1:

libavcodec/ac3dec.h

@@ -27,7 +27,7 @@
 #ifndef FFMPEG_AC3DEC_H
 #define FFMPEG_AC3DEC_H
 
-#include "libavutil/random.h"
+#include "libavutil/lfg.h"
 #include "ac3tab.h"
 #include "ac3.h"
 #include "bitstream.h"
@@ -143,7 +143,7 @@ typedef struct {
 ///@defgroup dithering zero-mantissa dithering
     int dither_all;                         ///< true if all channels are dithered
     int dither_flag[AC3_MAX_CHANNELS];      ///< dither flags                           (dithflg)
-    AVRandomState dith_state;               ///< for dither generation
+    AVLFG dith_state;                       ///< for dither generation
 ///@}
 
 ///@defgroup imdct IMDCT

libavutil/Makefile

@@ -9,6 +9,7 @@ OBJS = adler32.o \
        des.o \
        fifo.o \
        intfloat_readwrite.o \
+       lfg.o \
        lls.o \
        log.o \
        lzo.o \