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[188.193.170.75]) by smtp.gmail.com with ESMTPSA id lz27sm779419ejb.39.2020.11.19.23.25.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Nov 2020 23:25:25 -0800 (PST) From: Andreas Rheinhardt To: ffmpeg-devel@ffmpeg.org Date: Fri, 20 Nov 2020 08:19:49 +0100 Message-Id: <20201120072116.818090-77-andreas.rheinhardt@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20201120072116.818090-1-andreas.rheinhardt@gmail.com> References: <20201120072116.818090-1-andreas.rheinhardt@gmail.com> MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH v2 076/162] avcodec/mss4: Simplify creating VLC tables X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.20 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: Andreas Rheinhardt Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" The lengths of the codes used by the mss4 decoder are ascending from left to right and therefore the lengths can be run-length encoded and the codes can be easily derived from them. And this is how it is indeed done. Yet some things can nevertheless be improved: a) The number of entries of the current VLC is implicitly contained in the run-length table and needn't be externally prescribed. b) The maximum length of a code is just the length of the last code (given that the lengths are ascending), so there is no point in setting max_bits in the loop itself. c) One can offload the actual calculation of the codes to ff_init_vlc_from_lengths(). Signed-off-by: Andreas Rheinhardt --- libavcodec/mss4.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) diff --git a/libavcodec/mss4.c b/libavcodec/mss4.c index c421a07c5d..baf3c14d02 100644 --- a/libavcodec/mss4.c +++ b/libavcodec/mss4.c @@ -143,25 +143,21 @@ typedef struct MSS4Context { } MSS4Context; static av_cold int mss4_init_vlc(VLC *vlc, const uint8_t *lens, - const uint8_t *syms, int num_syms) + const uint8_t *syms) { uint8_t bits[MAX_ENTRIES]; - uint16_t codes[MAX_ENTRIES]; int i, j; - int prefix = 0, max_bits = 0, idx = 0; + int idx = 0; for (i = 0; i < 16; i++) { for (j = 0; j < lens[i]; j++) { bits[idx] = i + 1; - codes[idx] = prefix++; - max_bits = i + 1; idx++; } - prefix <<= 1; } - return ff_init_vlc_sparse(vlc, FFMIN(max_bits, 9), num_syms, bits, 1, 1, - codes, 2, 2, syms, 1, 1, 0); + return ff_init_vlc_from_lengths(vlc, FFMIN(bits[idx - 1], 9), idx, + bits, 1, syms, 1, 1, 0, 0, NULL); } static av_cold int mss4_init_vlcs(MSS4Context *ctx) @@ -169,15 +165,15 @@ static av_cold int mss4_init_vlcs(MSS4Context *ctx) int ret, i; for (i = 0; i < 2; i++) { - ret = mss4_init_vlc(&ctx->dc_vlc[i], mss4_dc_vlc_lens[i], NULL, 12); + ret = mss4_init_vlc(&ctx->dc_vlc[i], mss4_dc_vlc_lens[i], NULL); if (ret) return ret; ret = mss4_init_vlc(&ctx->ac_vlc[i], mss4_ac_vlc_lens[i], - mss4_ac_vlc_syms[i], 162); + mss4_ac_vlc_syms[i]); if (ret) return ret; ret = mss4_init_vlc(&ctx->vec_entry_vlc[i], mss4_vec_entry_vlc_lens[i], - mss4_vec_entry_vlc_syms[i], 9); + mss4_vec_entry_vlc_syms[i]); if (ret) return ret; }