[FFmpeg-devel] [PATCH v2] Replace arrays of pointers to strings by arrays of strings
Marton Balint
cus at passwd.hu
Wed Jan 6 11:34:52 EET 2021
On Wed, 6 Jan 2021, Andreas Rheinhardt wrote:
> When the difference of the longest size and the average size of
> collection of strings is smaller than the size of a pointer, it makes
> sense to store the strings directly in an array instead of using an
> array of pointers to strings (unless doing so precludes deduplicating
> strings); doing so also avoids relocations. This requirement is
> fulfilled for several arrays of pointers to strings that are changed in
> this commit.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
> Now used sizeof("longest string") for the array element size.
Duplicating the "longest string" is very ugly, I don't find it better than
a constant number, because a sizeof still does not say it tries to find
the longest string.
TBH I am not a fan of these kind of patches for a few byte of savings, and
when changing the list of strings it can actually become worse which won't
be checked by anybody...
Regards,
Marton
>
> I'd still like to know whether I can simply work under the assumption
> that pointers are 64bit when estimating whether other patches of this
> kind are worth it (some changes that are worth it in 64bit could
> actually be counterproductive size-wise for 32bit systems; but given
> that these patches avoid relocations, overestimating sizeof(char*)
> seems actually more accurate).
>
> libavcodec/ccaption_dec.c | 4 ++--
> libavcodec/vaapi_encode.c | 2 +-
> libavfilter/af_hdcd.c | 2 +-
> libavfilter/f_perms.c | 4 ++--
> libavformat/iff.c | 4 ++--
> libavformat/matroskadec.c | 2 +-
> libavformat/sdp.c | 2 +-
> libavutil/parseutils.c | 2 +-
> 8 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
> index a208e19b95..0198158c38 100644
> --- a/libavcodec/ccaption_dec.c
> +++ b/libavcodec/ccaption_dec.c
> @@ -66,7 +66,7 @@ enum cc_charset {
> CCSET_EXTENDED_PORTUGUESE_GERMAN_DANISH,
> };
>
> -static const char *charset_overrides[4][128] =
> +static const char charset_overrides[4][128][sizeof("\u266a")] =
> {
> [CCSET_BASIC_AMERICAN] = {
> [0x27] = "\u2019",
> @@ -575,7 +575,7 @@ static int capture_screen(CCaptionSubContext *ctx)
> prev_color = color[j];
> prev_bg_color = bg[j];
> override = charset_overrides[(int)charset[j]][(int)row[j]];
> - if (override) {
> + if (override[0]) {
> av_bprintf(&ctx->buffer[bidx], "%s%s%s%s%s", e_tag, s_tag, c_tag, b_tag, override);
> seen_char = 1;
> } else if (row[j] == ' ' && !seen_char) {
> diff --git a/libavcodec/vaapi_encode.c b/libavcodec/vaapi_encode.c
> index 518e5b2c00..d643046b5d 100644
> --- a/libavcodec/vaapi_encode.c
> +++ b/libavcodec/vaapi_encode.c
> @@ -33,7 +33,7 @@ const AVCodecHWConfigInternal *const ff_vaapi_encode_hw_configs[] = {
> NULL,
> };
>
> -static const char * const picture_type_name[] = { "IDR", "I", "P", "B" };
> +static const char picture_type_name[][sizeof("IDR")] = { "IDR", "I", "P", "B" };
>
> static int vaapi_encode_make_packed_header(AVCodecContext *avctx,
> VAAPIEncodePicture *pic,
> diff --git a/libavfilter/af_hdcd.c b/libavfilter/af_hdcd.c
> index 251d03229a..fc281a4620 100644
> --- a/libavfilter/af_hdcd.c
> +++ b/libavfilter/af_hdcd.c
> @@ -900,7 +900,7 @@ typedef enum {
> HDCD_PVER_MIX = 3, /**< Packets of type A and B discovered, most likely an encoding error */
> } hdcd_pf;
>
> -static const char * const pf_str[] = {
> +static const char pf_str[][sizeof("A+B")] = {
> "?", "A", "B", "A+B"
> };
>
> diff --git a/libavfilter/f_perms.c b/libavfilter/f_perms.c
> index d984e5b150..ae4264038f 100644
> --- a/libavfilter/f_perms.c
> +++ b/libavfilter/f_perms.c
> @@ -72,7 +72,7 @@ static av_cold int init(AVFilterContext *ctx)
> }
>
> enum perm { RO, RW };
> -static const char * const perm_str[2] = { "RO", "RW" };
> +static const char perm_str[] = { 'O', 'W' };
>
> static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
> {
> @@ -91,7 +91,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
> default: out_perm = in_perm; break;
> }
>
> - av_log(ctx, AV_LOG_VERBOSE, "%s -> %s%s\n",
> + av_log(ctx, AV_LOG_VERBOSE, "R%c -> R%c%s\n",
> perm_str[in_perm], perm_str[out_perm],
> in_perm == out_perm ? " (no-op)" : "");
>
> diff --git a/libavformat/iff.c b/libavformat/iff.c
> index 2dba121f6f..ad39e08649 100644
> --- a/libavformat/iff.c
> +++ b/libavformat/iff.c
> @@ -199,13 +199,13 @@ static const uint64_t dsd_loudspeaker_config[] = {
> AV_CH_LAYOUT_5POINT0, AV_CH_LAYOUT_5POINT1,
> };
>
> -static const char * dsd_source_comment[] = {
> +static const char dsd_source_comment[][sizeof("analogue_source_comment")] = {
> "dsd_source_comment",
> "analogue_source_comment",
> "pcm_source_comment",
> };
>
> -static const char * dsd_history_comment[] = {
> +static const char dsd_history_comment[][sizeof("creating_machine")] = {
> "general_remark",
> "operator_name",
> "creating_machine",
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 374831baa3..7b26face08 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -1946,7 +1946,7 @@ static void matroska_parse_cues(MatroskaDemuxContext *matroska) {
>
> static int matroska_aac_profile(char *codec_id)
> {
> - static const char *const aac_profiles[] = { "MAIN", "LC", "SSR" };
> + static const char aac_profiles[][sizeof("MAIN")] = { "MAIN", "LC", "SSR" };
> int profile;
>
> for (profile = 0; profile < FF_ARRAY_ELEMS(aac_profiles); profile++)
> diff --git a/libavformat/sdp.c b/libavformat/sdp.c
> index 95f3fbb876..69565e326d 100644
> --- a/libavformat/sdp.c
> +++ b/libavformat/sdp.c
> @@ -230,7 +230,7 @@ static char *extradata2psets_hevc(AVCodecParameters *par)
> int extradata_size = par->extradata_size;
> uint8_t *tmpbuf = NULL;
> int ps_pos[3] = { 0 };
> - static const char * const ps_names[3] = { "vps", "sps", "pps" };
> + static const char ps_names[3][sizeof("vps")] = { "vps", "sps", "pps" };
> int num_arrays, num_nalus;
> int pos, i, j;
>
> diff --git a/libavutil/parseutils.c b/libavutil/parseutils.c
> index 167e822648..e43c249cee 100644
> --- a/libavutil/parseutils.c
> +++ b/libavutil/parseutils.c
> @@ -140,7 +140,7 @@ static const VideoRateAbbr video_rate_abbrs[]= {
> { "ntsc-film", { 24000, 1001 } },
> };
>
> -static const char *months[12] = {
> +static const char months[12][sizeof("september")] = {
> "january", "february", "march", "april", "may", "june", "july", "august",
> "september", "october", "november", "december"
> };
> --
> 2.25.1
>
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