[FFmpeg-devel] [PATCH 8/9] avcodec/evc_parser: use a GetBitContext to parse entire NALUs

[James Almer <jamrial@gmail.com>]

Signed-off-by: James Almer <jamrial@gmail.com>
---
 libavcodec/evc_parse.c  | 22 ----------------------
 libavcodec/evc_parse.h  | 22 ----------------------
 libavcodec/evc_parser.c | 30 ++++++++++++------------------
 3 files changed, 12 insertions(+), 62 deletions(-)

diff --git a/libavcodec/evc_parse.c b/libavcodec/evc_parse.c
index dee48e947b..eff4b7bc38 100644
--- a/libavcodec/evc_parse.c
+++ b/libavcodec/evc_parse.c
@@ -21,28 +21,6 @@
 #include "evc.h"
 #include "evc_parse.h"
 
-// nuh_temporal_id specifies a temporal identifier for the NAL unit
-int ff_evc_get_temporal_id(const uint8_t *bits, int bits_size, void *logctx)
-{
-    int temporal_id = 0;
-    uint16_t t = 0;
-
-    if (bits_size < EVC_NALU_HEADER_SIZE) {
-        av_log(logctx, AV_LOG_ERROR, "Can't read NAL unit header\n");
-        return 0;
-    }
-
-    // forbidden_zero_bit
-    if ((bits[0] & 0x80) != 0)
-        return -1;
-
-    t = AV_RB16(bits);
-
-    temporal_id = (t >> 6) & 0x0007;
-
-    return temporal_id;
-}
-
 // @see ISO_IEC_23094-1 (7.3.2.6 Slice layer RBSP syntax)
 int ff_evc_parse_slice_header(GetBitContext *gb, EVCParserSliceHeader *sh,
                               const EVCParamSets *ps, enum EVCNALUnitType nalu_type)
diff --git a/libavcodec/evc_parse.h b/libavcodec/evc_parse.h
index 322f52c928..0f142976f5 100644
--- a/libavcodec/evc_parse.h
+++ b/libavcodec/evc_parse.h
@@ -81,25 +81,6 @@ typedef struct EVCParserPoc {
     int DocOffset;          // the decoding order count of the previous picture
 } EVCParserPoc;
 
-static inline int evc_get_nalu_type(const uint8_t *bits, int bits_size, void *logctx)
-{
-    int unit_type_plus1 = 0;
-
-    if (bits_size >= EVC_NALU_HEADER_SIZE) {
-        unsigned char *p = (unsigned char *)bits;
-        // forbidden_zero_bit
-        if ((p[0] & 0x80) != 0) {
-            av_log(logctx, AV_LOG_ERROR, "Invalid NAL unit header\n");
-            return -1;
-        }
-
-        // nal_unit_type
-        unit_type_plus1 = (p[0] >> 1) & 0x3F;
-    }
-
-    return unit_type_plus1 - 1;
-}
-
 static inline uint32_t evc_read_nal_unit_length(const uint8_t *bits, int bits_size, void *logctx)
 {
     uint32_t nalu_len = 0;
@@ -114,9 +95,6 @@ static inline uint32_t evc_read_nal_unit_length(const uint8_t *bits, int bits_si
     return nalu_len;
 }
 
-// nuh_temporal_id specifies a temporal identifier for the NAL unit
-int ff_evc_get_temporal_id(const uint8_t *bits, int bits_size, void *logctx);
-
 int ff_evc_parse_slice_header(GetBitContext *gb, EVCParserSliceHeader *sh,
                               const EVCParamSets *ps, enum EVCNALUnitType nalu_type);
 
diff --git a/libavcodec/evc_parser.c b/libavcodec/evc_parser.c
index ae399ef8cc..76790d8111 100644
--- a/libavcodec/evc_parser.c
+++ b/libavcodec/evc_parser.c
@@ -71,28 +71,29 @@ static int parse_nal_unit(AVCodecParserContext *s, AVCodecContext *avctx,
         return AVERROR_INVALIDDATA;
     }
 
+    ret = init_get_bits8(&gb, buf, buf_size);
+    if (ret < 0)
+        return ret;
+
     // @see ISO_IEC_23094-1_2020, 7.4.2.2 NAL unit header semantic (Table 4 - NAL unit type codes and NAL unit type classes)
     // @see enum EVCNALUnitType in evc.h
-    nalu_type = evc_get_nalu_type(buf, buf_size, avctx);
-    if (nalu_type < EVC_NOIDR_NUT || nalu_type > EVC_UNSPEC_NUT62) {
-        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit type: (%d)\n", nalu_type);
+    if (get_bits1(&gb)) {// forbidden_zero_bit
+        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit header\n");
         return AVERROR_INVALIDDATA;
     }
 
-    tid = ff_evc_get_temporal_id(buf, buf_size, avctx);
-    if (tid < 0) {
-        av_log(avctx, AV_LOG_ERROR, "Invalid temporial id: (%d)\n", tid);
+    nalu_type = get_bits(&gb, 6) - 1;
+    if (nalu_type < EVC_NOIDR_NUT || nalu_type > EVC_UNSPEC_NUT62) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid NAL unit type: (%d)\n", nalu_type);
         return AVERROR_INVALIDDATA;
     }
 
-    buf += EVC_NALU_HEADER_SIZE;
-    buf_size -= EVC_NALU_HEADER_SIZE;
+    tid = get_bits(&gb, 3);
+    skip_bits(&gb, 5); // nuh_reserved_zero_5bits
+    skip_bits1(&gb);   // nuh_extension_flag
 
     switch (nalu_type) {
     case EVC_SPS_NUT:
-        ret = init_get_bits8(&gb, buf, buf_size);
-        if (ret < 0)
-            return ret;
         ret = ff_evc_parse_sps(&gb, &ctx->ps);
         if (ret < 0) {
             av_log(avctx, AV_LOG_ERROR, "SPS parsing error\n");
@@ -100,9 +101,6 @@ static int parse_nal_unit(AVCodecParserContext *s, AVCodecContext *avctx,
         }
         break;
     case EVC_PPS_NUT:
-        ret = init_get_bits8(&gb, buf, buf_size);
-        if (ret < 0)
-            return ret;
         ret = ff_evc_parse_pps(&gb, &ctx->ps);
         if (ret < 0) {
             av_log(avctx, AV_LOG_ERROR, "PPS parsing error\n");
@@ -116,10 +114,6 @@ static int parse_nal_unit(AVCodecParserContext *s, AVCodecContext *avctx,
         EVCParserSliceHeader sh;
         int bit_depth;
 
-        ret = init_get_bits8(&gb, buf, buf_size);
-        if (ret < 0)
-            return ret;
-
         ret = ff_evc_parse_slice_header(&gb, &sh, &ctx->ps, nalu_type);
         if (ret < 0) {
             av_log(avctx, AV_LOG_ERROR, "Slice header parsing error\n");
-- 
2.41.0

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