mpeg1: Make intra-block decoding independent of MpegEncContext

This allows untangling the eatqi decoder from the MPEG-1 decoder.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
Signed-off-by: Diego Biurrun <diego@biurrun.de>

1 files changed, 88 insertions, 0 deletions

diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
index 69c6d0a09a..c0c680d867 100644
--- a/libavcodec/mpeg12.c
+++ b/libavcodec/mpeg12.c
@@ -236,3 +236,91 @@ int ff_mpeg1_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size,
     pc->state = state;
     return END_NOT_FOUND;
 }
+
+#define MAX_INDEX (64 - 1)
+
+int ff_mpeg1_decode_block_intra(GetBitContext *gb,
+                                const uint16_t *quant_matrix,
+                                uint8_t *const scantable, int last_dc[3],
+                                int16_t *block, int index, int qscale)
+{
+    int dc, diff, i = 0, component;
+    RLTable *rl = &ff_rl_mpeg1;
+
+    /* DC coefficient */
+    component = index <= 3 ? 0 : index - 4 + 1;
+
+    diff = decode_dc(gb, component);
+    if (diff >= 0xffff)
+        return AVERROR_INVALIDDATA;
+
+    dc  = last_dc[component];
+    dc += diff;
+    last_dc[component] = dc;
+
+    block[0] = dc * quant_matrix[0];
+
+    {
+        OPEN_READER(re, gb);
+        /* now quantify & encode AC coefficients */
+        while (1) {
+            int level, run, j;
+
+            UPDATE_CACHE(re, gb);
+            GET_RL_VLC(level, run, re, gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);
+
+            if (level == 127) {
+                break;
+            } else if (level != 0) {
+                i += run;
+                if (i > MAX_INDEX)
+                    break;
+
+                j = scantable[i];
+                level = (level * qscale * quant_matrix[j]) >> 4;
+                level = (level - 1) | 1;
+                level = (level ^ SHOW_SBITS(re, gb, 1)) -
+                        SHOW_SBITS(re, gb, 1);
+                LAST_SKIP_BITS(re, gb, 1);
+            } else {
+                /* escape */
+                run = SHOW_UBITS(re, gb, 6) + 1;
+                LAST_SKIP_BITS(re, gb, 6);
+                UPDATE_CACHE(re, gb);
+                level = SHOW_SBITS(re, gb, 8);
+                SKIP_BITS(re, gb, 8);
+
+                if (level == -128) {
+                    level = SHOW_UBITS(re, gb, 8) - 256;
+                    LAST_SKIP_BITS(re, gb, 8);
+                } else if (level == 0) {
+                    level = SHOW_UBITS(re, gb, 8);
+                    LAST_SKIP_BITS(re, gb, 8);
+                }
+
+                i += run;
+                if (i > MAX_INDEX)
+                    break;
+
+                j = scantable[i];
+                if (level < 0) {
+                    level = -level;
+                    level = (level * qscale * quant_matrix[j]) >> 4;
+                    level = (level - 1) | 1;
+                    level = -level;
+                } else {
+                    level = (level * qscale * quant_matrix[j]) >> 4;
+                    level = (level - 1) | 1;
+                }
+            }
+
+            block[j] = level;
+        }
+        CLOSE_READER(re, gb);
+    }
+
+    if (i > MAX_INDEX)
+        i = AVERROR_INVALIDDATA;
+
+    return i;
+}