[FFmpeg-devel] [PATCH 044/114] avcodec/mpc8: Reduce the size of some VLCs

[Andreas Rheinhardt]

Several of the quantisation VLCs come in pairs and up until now the
number of bits used for each VLC was set to the same value for both VLCs
in such a pair even when one of the two required only a lower number.
This is a waste given that the get_vlc2() call is compatible with these
two VLCs using a different number of bits (it uses vlc->bits).

Given that the code lengths are descending it is easily possible to know
the length of the longest code for a given VLC: It is the length of the
first one. With this information one can easily use the least amount of
bits.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
 libavcodec/mpc8.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/libavcodec/mpc8.c b/libavcodec/mpc8.c
index ef0fd6622a..4863ec0953 100644
--- a/libavcodec/mpc8.c
+++ b/libavcodec/mpc8.c
@@ -87,10 +87,10 @@ static int mpc8_get_mask(GetBitContext *gb, int size, int t)
 }
 
 static const uint16_t vlc_offsets[13] = {
-    0, 640, 1184, 1748, 2298, 2426, 2554, 3066, 3578, 4106, 4618, 5196, 5708
+    0, 640, 1184, 1748, 2298, 2426, 2490, 3002, 3258, 3786, 4298, 4876, 5388
 };
 
-static av_cold void build_vlc(VLC *vlc, int nb_bits,
+static av_cold void build_vlc(VLC *vlc,
                               const uint8_t codes_counts[16],
                               const uint8_t syms[], int offset)
 {
@@ -101,7 +101,7 @@ static av_cold void build_vlc(VLC *vlc, int nb_bits,
         for (unsigned tmp = num + codes_counts[i - 1]; num < tmp; num++)
             len[num] = i;
 
-    ff_init_vlc_from_lengths(vlc, nb_bits, num, len, 1,
+    ff_init_vlc_from_lengths(vlc, FFMIN(len[0], 9), num, len, 1,
                              syms, 1, 1, offset, INIT_VLC_USE_NEW_STATIC);
 }
 
@@ -112,7 +112,7 @@ static av_cold int mpc8_decode_init(AVCodecContext * avctx)
     GetBitContext gb;
     static int vlc_initialized = 0;
     int channels;
-    static VLC_TYPE codes_table[5708][2];
+    static VLC_TYPE codes_table[5388][2];
 
     if(avctx->extradata_size < 2){
         av_log(avctx, AV_LOG_ERROR, "Too small extradata size (%i)!\n", avctx->extradata_size);
@@ -152,7 +152,7 @@ static av_cold int mpc8_decode_init(AVCodecContext * avctx)
         static VLC_TYPE table[static_size][2];                             \
         (vlc)->table           = table;                                    \
         (vlc)->table_allocated = static_size;                              \
-        build_vlc(vlc, bits, len_counts, symbols, offset);                 \
+        build_vlc(vlc, len_counts, symbols, offset);                       \
     } while (0)
 
 
@@ -182,29 +182,29 @@ static av_cold int mpc8_decode_init(AVCodecContext * avctx)
     for(i = 0; i < 2; i++){
         res_vlc[i].table = &codes_table[vlc_offsets[0+i]];
         res_vlc[i].table_allocated = vlc_offsets[1+i] - vlc_offsets[0+i];
-        build_vlc(&res_vlc[i], MPC8_RES_BITS,
+        build_vlc(&res_vlc[i],
                   mpc8_res_len_counts[i], mpc8_res_syms[i], 0);
 
         q2_vlc[i].table = &codes_table[vlc_offsets[2+i]];
         q2_vlc[i].table_allocated = vlc_offsets[3+i] - vlc_offsets[2+i];
-        build_vlc(&q2_vlc[i], MPC8_Q2_BITS,
+        build_vlc(&q2_vlc[i],
                   mpc8_q2_len_counts[i], mpc8_q2_syms[i], 0);
 
         quant_vlc[0][i].table = &codes_table[vlc_offsets[4+i]];
         quant_vlc[0][i].table_allocated = vlc_offsets[5+i] - vlc_offsets[4+i];
-        build_vlc(&quant_vlc[0][i], MPC8_Q5_BITS,
+        build_vlc(&quant_vlc[0][i],
                   mpc8_q5_len_counts[i], mpc8_q5_syms[i], MPC8_Q5_OFFSET);
         quant_vlc[1][i].table = &codes_table[vlc_offsets[6+i]];
         quant_vlc[1][i].table_allocated = vlc_offsets[7+i] - vlc_offsets[6+i];
-        build_vlc(&quant_vlc[1][i], MPC8_Q6_BITS,
+        build_vlc(&quant_vlc[1][i],
                   mpc8_q6_len_counts[i], mpc8_q6_syms[i], MPC8_Q6_OFFSET);
         quant_vlc[2][i].table = &codes_table[vlc_offsets[8+i]];
         quant_vlc[2][i].table_allocated = vlc_offsets[9+i] - vlc_offsets[8+i];
-        build_vlc(&quant_vlc[2][i], MPC8_Q7_BITS,
+        build_vlc(&quant_vlc[2][i],
                   mpc8_q7_len_counts[i], mpc8_q7_syms[i], MPC8_Q7_OFFSET);
         quant_vlc[3][i].table = &codes_table[vlc_offsets[10+i]];
         quant_vlc[3][i].table_allocated = vlc_offsets[11+i] - vlc_offsets[10+i];
-        build_vlc(&quant_vlc[3][i], MPC8_Q8_BITS,
+        build_vlc(&quant_vlc[3][i],
                   mpc8_q8_len_counts[i], mpc8_q8_syms[i], MPC8_Q8_OFFSET);
     }
     vlc_initialized = 1;
-- 
2.25.1