From dddb5f72a2accc0b956d1ab8c4108745a924e736 Mon Sep 17 00:00:00 2001
From: HolyWu <holywu@gmail.com>
Date: Mon, 17 May 2021 11:24:41 +0800
Subject: [PATCH] Revert "vc-1: Optimise parser (with special attention to
 ARM)"

This reverts commit 701e8b42e12ad625c64ceae2252acb1de390278c.

The optimized VC-1 parser did not parse properties of pictures at all and it could cause seeking issues.
---
 libavcodec/vc1_parser.c | 305 +++++++++++++++-------------------------
 1 file changed, 115 insertions(+), 190 deletions(-)

diff --git a/libavcodec/vc1_parser.c b/libavcodec/vc1_parser.c
index 493ffde61104c..7016df06e71da 100644
--- a/libavcodec/vc1_parser.c
+++ b/libavcodec/vc1_parser.c
@@ -31,98 +31,132 @@
 #include "get_bits.h"
 #include "internal.h"
 
-/** The maximum number of bytes of a sequence, entry point or
- *  frame header whose values we pay any attention to */
-#define UNESCAPED_THRESHOLD 37
-
-/** The maximum number of bytes of a sequence, entry point or
- *  frame header which must be valid memory (because they are
- *  used to update the bitstream cache in skip_bits() calls)
- */
-#define UNESCAPED_LIMIT 144
-
-typedef enum {
-    NO_MATCH,
-    ONE_ZERO,
-    TWO_ZEROS,
-    ONE
-} VC1ParseSearchState;
-
 typedef struct VC1ParseContext {
     ParseContext pc;
     VC1Context v;
-    uint8_t prev_start_code;
-    size_t bytes_to_skip;
-    uint8_t unesc_buffer[UNESCAPED_LIMIT];
-    size_t unesc_index;
-    VC1ParseSearchState search_state;
 } VC1ParseContext;
 
-static void vc1_extract_header(AVCodecParserContext *s, AVCodecContext *avctx,
-                               const uint8_t *buf, int buf_size)
+static void vc1_extract_headers(AVCodecParserContext *s, AVCodecContext *avctx,
+                                const uint8_t *buf, int buf_size)
 {
-    /* Parse the header we just finished unescaping */
     VC1ParseContext *vpc = s->priv_data;
     GetBitContext gb;
-    int ret;
+    const uint8_t *start, *end, *next;
+    uint8_t *buf2 = av_mallocz(buf_size + AV_INPUT_BUFFER_PADDING_SIZE);
+
     vpc->v.s.avctx = avctx;
     vpc->v.parse_only = 1;
-    init_get_bits8(&gb, buf, buf_size);
-    switch (vpc->prev_start_code) {
-    case VC1_CODE_SEQHDR & 0xFF:
-        ff_vc1_decode_sequence_header(avctx, &vpc->v, &gb);
-        break;
-    case VC1_CODE_ENTRYPOINT & 0xFF:
-        ff_vc1_decode_entry_point(avctx, &vpc->v, &gb);
-        break;
-    case VC1_CODE_FRAME & 0xFF:
-        if(vpc->v.profile < PROFILE_ADVANCED)
-            ret = ff_vc1_parse_frame_header    (&vpc->v, &gb);
-        else
-            ret = ff_vc1_parse_frame_header_adv(&vpc->v, &gb);
-
-        if (ret < 0)
+    vpc->v.first_pic_header_flag = 1;
+    next = buf;
+    s->repeat_pict = 0;
+
+    for(start = buf, end = buf + buf_size; next < end; start = next){
+        int buf2_size, size;
+        int ret;
+
+        next = find_next_marker(start + 4, end);
+        size = next - start - 4;
+        buf2_size = vc1_unescape_buffer(start + 4, size, buf2);
+        init_get_bits8(&gb, buf2, buf2_size);
+        if(size <= 0) continue;
+        switch(AV_RB32(start)){
+        case VC1_CODE_SEQHDR:
+            ff_vc1_decode_sequence_header(avctx, &vpc->v, &gb);
+            break;
+        case VC1_CODE_ENTRYPOINT:
+            ff_vc1_decode_entry_point(avctx, &vpc->v, &gb);
             break;
+        case VC1_CODE_FRAME:
+            if(vpc->v.profile < PROFILE_ADVANCED)
+                ret = ff_vc1_parse_frame_header    (&vpc->v, &gb);
+            else
+                ret = ff_vc1_parse_frame_header_adv(&vpc->v, &gb);
 
-        /* keep AV_PICTURE_TYPE_BI internal to VC1 */
-        if (vpc->v.s.pict_type == AV_PICTURE_TYPE_BI)
-            s->pict_type = AV_PICTURE_TYPE_B;
-        else
-            s->pict_type = vpc->v.s.pict_type;
+            if (ret < 0)
+                break;
 
-        if (avctx->ticks_per_frame > 1){
-            // process pulldown flags
-            s->repeat_pict = 1;
-            // Pulldown flags are only valid when 'broadcast' has been set.
-            // So ticks_per_frame will be 2
-            if (vpc->v.rff){
-                // repeat field
-                s->repeat_pict = 2;
-            }else if (vpc->v.rptfrm){
-                // repeat frames
-                s->repeat_pict = vpc->v.rptfrm * 2 + 1;
+            /* keep AV_PICTURE_TYPE_BI internal to VC1 */
+            if (vpc->v.s.pict_type == AV_PICTURE_TYPE_BI)
+                s->pict_type = AV_PICTURE_TYPE_B;
+            else
+                s->pict_type = vpc->v.s.pict_type;
+
+            if (avctx->ticks_per_frame > 1){
+                // process pulldown flags
+                s->repeat_pict = 1;
+                // Pulldown flags are only valid when 'broadcast' has been set.
+                // So ticks_per_frame will be 2
+                if (vpc->v.rff){
+                    // repeat field
+                    s->repeat_pict = 2;
+                }else if (vpc->v.rptfrm){
+                    // repeat frames
+                    s->repeat_pict = vpc->v.rptfrm * 2 + 1;
+                }
             }
-        }else{
-            s->repeat_pict = 0;
+
+            if (vpc->v.broadcast && vpc->v.interlace && !vpc->v.psf)
+                s->field_order = vpc->v.tff ? AV_FIELD_TT : AV_FIELD_BB;
+            else
+                s->field_order = AV_FIELD_PROGRESSIVE;
+
+            break;
+        }
+        if (avctx->framerate.num)
+            avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1}));
+        s->format = vpc->v.chromaformat == 1 ? AV_PIX_FMT_YUV420P
+                                             : AV_PIX_FMT_NONE;
+        if (avctx->width && avctx->height) {
+            s->width        = avctx->width;
+            s->height       = avctx->height;
+            s->coded_width  = FFALIGN(avctx->coded_width,  16);
+            s->coded_height = FFALIGN(avctx->coded_height, 16);
         }
+    }
 
-        if (vpc->v.broadcast && vpc->v.interlace && !vpc->v.psf)
-            s->field_order = vpc->v.tff ? AV_FIELD_TT : AV_FIELD_BB;
-        else
-            s->field_order = AV_FIELD_PROGRESSIVE;
+    av_free(buf2);
+}
 
-        break;
+/**
+ * Find the end of the current frame in the bitstream.
+ * @return the position of the first byte of the next frame, or -1
+ */
+static int vc1_find_frame_end(ParseContext *pc, const uint8_t *buf,
+                               int buf_size) {
+    int pic_found, i;
+    uint32_t state;
+
+    pic_found= pc->frame_start_found;
+    state= pc->state;
+
+    i=0;
+    if(!pic_found){
+        for(i=0; i<buf_size; i++){
+            state= (state<<8) | buf[i];
+            if(state == VC1_CODE_FRAME || state == VC1_CODE_FIELD){
+                i++;
+                pic_found=1;
+                break;
+            }
+        }
     }
-    if (avctx->framerate.num)
-        avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1}));
-    s->format = vpc->v.chromaformat == 1 ? AV_PIX_FMT_YUV420P
-                                         : AV_PIX_FMT_NONE;
-    if (avctx->width && avctx->height) {
-        s->width        = avctx->width;
-        s->height       = avctx->height;
-        s->coded_width  = FFALIGN(avctx->coded_width,  16);
-        s->coded_height = FFALIGN(avctx->coded_height, 16);
+
+    if(pic_found){
+        /* EOF considered as end of frame */
+        if (buf_size == 0)
+            return 0;
+        for(; i<buf_size; i++){
+            state= (state<<8) | buf[i];
+            if(IS_MARKER(state) && state != VC1_CODE_FIELD && state != VC1_CODE_SLICE){
+                pc->frame_start_found=0;
+                pc->state=-1;
+                return i-3;
+            }
+        }
     }
+    pc->frame_start_found= pic_found;
+    pc->state= state;
+    return END_NOT_FOUND;
 }
 
 static int vc1_parse(AVCodecParserContext *s,
@@ -130,126 +164,22 @@ static int vc1_parse(AVCodecParserContext *s,
                            const uint8_t **poutbuf, int *poutbuf_size,
                            const uint8_t *buf, int buf_size)
 {
-    /* Here we do the searching for frame boundaries and headers at
-     * the same time. Only a minimal amount at the start of each
-     * header is unescaped. */
     VC1ParseContext *vpc = s->priv_data;
-    int pic_found = vpc->pc.frame_start_found;
-    uint8_t *unesc_buffer = vpc->unesc_buffer;
-    size_t unesc_index = vpc->unesc_index;
-    VC1ParseSearchState search_state = vpc->search_state;
-    int start_code_found = 0;
-    int next = END_NOT_FOUND;
-    int i = vpc->bytes_to_skip;
+    int next;
 
-    if (pic_found && buf_size == 0) {
-        /* EOF considered as end of frame */
-        memset(unesc_buffer + unesc_index, 0, UNESCAPED_THRESHOLD - unesc_index);
-        vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
-        next = 0;
-    }
-    while (i < buf_size) {
-        uint8_t b;
-        start_code_found = 0;
-        while (i < buf_size && unesc_index < UNESCAPED_THRESHOLD) {
-            b = buf[i++];
-            unesc_buffer[unesc_index++] = b;
-            if (search_state <= ONE_ZERO)
-                search_state = b ? NO_MATCH : search_state + 1;
-            else if (search_state == TWO_ZEROS) {
-                if (b == 1)
-                    search_state = ONE;
-                else if (b > 1) {
-                    if (b == 3)
-                        unesc_index--; // swallow emulation prevention byte
-                    search_state = NO_MATCH;
-                }
-            }
-            else { // search_state == ONE
-                // Header unescaping terminates early due to detection of next start code
-                search_state = NO_MATCH;
-                start_code_found = 1;
-                break;
-            }
-        }
-        if ((s->flags & PARSER_FLAG_COMPLETE_FRAMES) &&
-                unesc_index >= UNESCAPED_THRESHOLD &&
-                vpc->prev_start_code == (VC1_CODE_FRAME & 0xFF))
-        {
-            // No need to keep scanning the rest of the buffer for
-            // start codes if we know it contains a complete frame and
-            // we've already unescaped all we need of the frame header
-            vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
-            break;
-        }
-        if (unesc_index >= UNESCAPED_THRESHOLD && !start_code_found) {
-            while (i < buf_size) {
-                if (search_state == NO_MATCH) {
-                    i += vpc->v.vc1dsp.startcode_find_candidate(buf + i, buf_size - i);
-                    if (i < buf_size) {
-                        search_state = ONE_ZERO;
-                    }
-                    i++;
-                } else {
-                    b = buf[i++];
-                    if (search_state == ONE_ZERO)
-                        search_state = b ? NO_MATCH : TWO_ZEROS;
-                    else if (search_state == TWO_ZEROS) {
-                        if (b >= 1)
-                            search_state = b == 1 ? ONE : NO_MATCH;
-                    }
-                    else { // search_state == ONE
-                        search_state = NO_MATCH;
-                        start_code_found = 1;
-                        break;
-                    }
-                }
-            }
-        }
-        if (start_code_found) {
-            vc1_extract_header(s, avctx, unesc_buffer, unesc_index);
-
-            vpc->prev_start_code = b;
-            unesc_index = 0;
+    if(s->flags & PARSER_FLAG_COMPLETE_FRAMES){
+        next= buf_size;
+    }else{
+        next= vc1_find_frame_end(&vpc->pc, buf, buf_size);
 
-            if (!(s->flags & PARSER_FLAG_COMPLETE_FRAMES)) {
-                if (!pic_found && (b == (VC1_CODE_FRAME & 0xFF) || b == (VC1_CODE_FIELD & 0xFF))) {
-                    pic_found = 1;
-                }
-                else if (pic_found && b != (VC1_CODE_FIELD & 0xFF) && b != (VC1_CODE_SLICE & 0xFF)) {
-                    next = i - 4;
-                    pic_found = b == (VC1_CODE_FRAME & 0xFF);
-                    break;
-                }
-            }
-        }
-    }
-
-    vpc->pc.frame_start_found = pic_found;
-    vpc->unesc_index = unesc_index;
-    vpc->search_state = search_state;
-
-    if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
-        next = buf_size;
-    } else {
         if (ff_combine_frame(&vpc->pc, next, &buf, &buf_size) < 0) {
-            vpc->bytes_to_skip = 0;
             *poutbuf = NULL;
             *poutbuf_size = 0;
             return buf_size;
         }
     }
 
-    /* If we return with a valid pointer to a combined frame buffer
-     * then on the next call then we'll have been unhelpfully rewound
-     * by up to 4 bytes (depending upon whether the start code
-     * overlapped the input buffer, and if so by how much). We don't
-     * want this: it will either cause spurious second detections of
-     * the start code we've already seen, or cause extra bytes to be
-     * inserted at the start of the unescaped buffer. */
-    vpc->bytes_to_skip = 4;
-    if (next < 0 && next != END_NOT_FOUND)
-        vpc->bytes_to_skip += next;
+    vc1_extract_headers(s, avctx, buf, buf_size);
 
     *poutbuf = buf;
     *poutbuf_size = buf_size;
@@ -265,9 +195,9 @@ static int vc1_split(AVCodecContext *avctx,
 
     while (ptr < end) {
         ptr = avpriv_find_start_code(ptr, end, &state);
-        if (state == VC1_CODE_SEQHDR || state == VC1_CODE_ENTRYPOINT) {
+        if (state == VC1_CODE_SEQHDR || state == VC1_CODE_ENTRYPOINT)
             charged = 1;
-        } else if (charged && IS_MARKER(state))
+        else if (charged && IS_MARKER(state))
             return ptr - 4 - buf;
     }
 
@@ -278,11 +208,6 @@ static av_cold int vc1_parse_init(AVCodecParserContext *s)
 {
     VC1ParseContext *vpc = s->priv_data;
     vpc->v.s.slice_context_count = 1;
-    vpc->v.first_pic_header_flag = 1;
-    vpc->prev_start_code = 0;
-    vpc->bytes_to_skip = 0;
-    vpc->unesc_index = 0;
-    vpc->search_state = NO_MATCH;
     return ff_vc1_init_common(&vpc->v);
 }