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Tue, 08 Feb 2022 12:32:22 -0800 (PST) Received: from localhost.localdomain ([151.200.235.219]) by smtp.gmail.com with ESMTPSA id g10sm7604701qti.45.2022.02.08.12.32.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Feb 2022 12:32:21 -0800 (PST) From: Scott Theisen To: ffmpeg-devel@ffmpeg.org Date: Tue, 8 Feb 2022 15:32:14 -0500 Message-Id: <20220208203214.161469-1-scott.the.elm@gmail.com> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH] cbs_mpeg2_split_fragment(): cache the buffer end X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Scott Theisen Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" X-TUID: b79H9rt0xqMS Also add a few clarifying comments. --- libavcodec/cbs_mpeg2.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c index 33bd3e0998..47732562d1 100644 --- a/libavcodec/cbs_mpeg2.c +++ b/libavcodec/cbs_mpeg2.c @@ -144,12 +144,12 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx, CodedBitstreamFragment *frag, int header) { - const uint8_t *start; + const uint8_t *start = frag->data; + const uint8_t * const buf_end = frag->data + frag->data_size; uint32_t start_code = -1; int err; - start = avpriv_find_start_code(frag->data, frag->data + frag->data_size, - &start_code); + start = avpriv_find_start_code(start, buf_end, &start_code); if (start_code >> 8 != 0x000001) { // No start code found. return AVERROR_INVALIDDATA; @@ -165,12 +165,11 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx, // start code in any way (as e.g. happens when there is a // Sequence End unit at the very end of a packet). start_code = UINT32_MAX; - end = avpriv_find_start_code(start--, frag->data + frag->data_size, - &start_code); - - // start points to the byte containing the start_code_identifier + end = avpriv_find_start_code(start, buf_end, &start_code); + start--; + // decrement so start points to the byte containing the start_code_identifier // (may be the last byte of fragment->data); end points to the byte - // following the byte containing the start code identifier (or to + // following the byte containing the next start code identifier (or to // the end of fragment->data). if (start_code >> 8 == 0x000001) { // Unit runs from start to the beginning of the start code @@ -178,6 +177,7 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx, unit_size = (end - 4) - start; } else { // We didn't find a start code, so this is the final unit. + // There is no start code to remove from end, hence not (end - 4). unit_size = end - start; }