h264: store {curr,max}_pic_num in the per-slice context

While the value of those variables will be constant for the whole frame,
they are only used in two functions called from slice header decoding.
Moving them to the per-slice context allows us to make the H264Context
passed to slice_header_parse() constant.

libavcodec/h264.h

@@ -451,6 +451,8 @@ typedef struct H264SliceContext {
     int poc_lsb;
     int delta_poc_bottom;
     int delta_poc[2];
+    int curr_pic_num;
+    int max_pic_num;
 } H264SliceContext;
 
 /**
@@ -565,16 +567,6 @@ typedef struct H264Context {
 
     H264POCContext poc;
 
-    /**
-     * frame_num for frames or 2 * frame_num + 1 for field pics.
-     */
-    int curr_pic_num;
-
-    /**
-     * max_frame_num or 2 * max_frame_num for field pics.
-     */
-    int max_pic_num;
-
     H264Picture *short_ref[32];
     H264Picture *long_ref[32];
     H264Picture *delayed_pic[MAX_DELAYED_PIC_COUNT + 2]; // FIXME size?

libavcodec/h264_refs.c

@@ -262,7 +262,7 @@ int ff_h264_build_ref_list(const H264Context *h, H264SliceContext *sl)
     h264_initialise_ref_list(h, sl);
 
     for (list = 0; list < sl->list_count; list++) {
-        int pred = h->curr_pic_num;
+        int pred = sl->curr_pic_num;
 
         for (index = 0; index < sl->nb_ref_modifications[list]; index++) {
             unsigned int modification_of_pic_nums_idc = sl->ref_modifications[list][index].op;
@@ -277,7 +277,7 @@ int ff_h264_build_ref_list(const H264Context *h, H264SliceContext *sl)
                 const unsigned int abs_diff_pic_num = val + 1;
                 int frame_num;
 
-                if (abs_diff_pic_num > h->max_pic_num) {
+                if (abs_diff_pic_num > sl->max_pic_num) {
                     av_log(h->avctx, AV_LOG_ERROR,
                            "abs_diff_pic_num overflow\n");
                     return AVERROR_INVALIDDATA;
@@ -287,7 +287,7 @@ int ff_h264_build_ref_list(const H264Context *h, H264SliceContext *sl)
                     pred -= abs_diff_pic_num;
                 else
                     pred += abs_diff_pic_num;
-                pred &= h->max_pic_num - 1;
+                pred &= sl->max_pic_num - 1;
 
                 frame_num = pic_num_extract(h, pred, &pic_structure);
 
@@ -751,8 +751,8 @@ int ff_h264_decode_ref_pic_marking(const H264Context *h, H264SliceContext *sl,
                 mmco[i].opcode = opcode;
                 if (opcode == MMCO_SHORT2UNUSED || opcode == MMCO_SHORT2LONG) {
                     mmco[i].short_pic_num =
-                        (h->curr_pic_num - get_ue_golomb(gb) - 1) &
-                            (h->max_pic_num - 1);
+                        (sl->curr_pic_num - get_ue_golomb(gb) - 1) &
+                            (sl->max_pic_num - 1);
 #if 0
                     if (mmco[i].short_pic_num >= h->short_ref_count ||
                         !h->short_ref[mmco[i].short_pic_num]) {

libavcodec/h264_slice.c

@@ -405,9 +405,6 @@ int ff_h264_update_thread_context(AVCodecContext *dst,
 
     memcpy(&h->poc,        &h1->poc,        sizeof(h->poc));
 
-    h->curr_pic_num      = h1->curr_pic_num;
-    h->max_pic_num       = h1->max_pic_num;
-
     memcpy(h->short_ref,   h1->short_ref,   sizeof(h->short_ref));
     memcpy(h->long_ref,    h1->long_ref,    sizeof(h->long_ref));
     memcpy(h->delayed_pic, h1->delayed_pic, sizeof(h->delayed_pic));
@@ -1173,7 +1170,7 @@ static int h264_field_start(H264Context *h, const H264SliceContext *sl,
     return 0;
 }
 
-static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
+static int h264_slice_header_parse(const H264Context *h, H264SliceContext *sl,
                                    const H2645NAL *nal)
 {
     const SPS *sps;
@@ -1248,11 +1245,11 @@ static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
     sl->mb_field_decoding_flag = picture_structure != PICT_FRAME;
 
     if (picture_structure == PICT_FRAME) {
-        h->curr_pic_num = sl->frame_num;
-        h->max_pic_num  = 1 << sps->log2_max_frame_num;
+        sl->curr_pic_num = sl->frame_num;
+        sl->max_pic_num  = 1 << sps->log2_max_frame_num;
     } else {
-        h->curr_pic_num = 2 * sl->frame_num + 1;
-        h->max_pic_num  = 1 << (sps->log2_max_frame_num + 1);
+        sl->curr_pic_num = 2 * sl->frame_num + 1;
+        sl->max_pic_num  = 1 << (sps->log2_max_frame_num + 1);
     }
 
     if (nal->type == NAL_IDR_SLICE)