[FFmpeg-devel] [PATCH 05/30] Replace arrays of pointers to strings by arrays of strings

[Andreas Rheinhardt]

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>
---
1. The changes to ccaption_dec (which provide the largest savings of
this patchset) require \u to yield UTF-8; I hope this is ok. Notice that
if it were otherwise we would already output non UTF-8.
2. Whether it is worthwhile to replace arrays of pointers to strings by
arrays of strings depends of course upon the size of pointers. Do I need
to take 32bit systems into account for further patches like this here?
3. On 64bit Elf systems every one of these relocations takes 24bytes; it
is less on Windows. Here is more about this:
https://chromium.googlesource.com/chromium/src/+/master/docs/native_relocations.md

 libavcodec/ccaption_dec.c | 4 ++--
 libavcodec/vaapi_encode.c | 2 +-
 libavfilter/af_hdcd.c     | 2 +-
 libavfilter/f_perms.c     | 2 +-
 libavformat/iff.c         | 4 ++--
 libavformat/matroskadec.c | 2 +-
 libavformat/sdp.c         | 2 +-
 libavutil/parseutils.c    | 2 +-
 8 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
index a208e19b95..c864416241 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][4] =
 {
     [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..a47facc46d 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[][4] = { "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..7000ea81de 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[][4] = {
     "?", "A", "B", "A+B"
 };
 
diff --git a/libavfilter/f_perms.c b/libavfilter/f_perms.c
index d984e5b150..ad52a4ed6e 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[2][4] = { "RO", "RW" };
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
 {
diff --git a/libavformat/iff.c b/libavformat/iff.c
index 2dba121f6f..53abd6d168 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[][24] = {
     "dsd_source_comment",
     "analogue_source_comment",
     "pcm_source_comment",
 };
 
-static const char * dsd_history_comment[] = {
+static const char dsd_history_comment[][17] = {
     "general_remark",
     "operator_name",
     "creating_machine",
diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index 374831baa3..300ccae0ad 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[][5] = { "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..5a0e1695c9 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][4] = { "vps", "sps", "pps" };
     int num_arrays, num_nalus;
     int pos, i, j;
 
diff --git a/libavutil/parseutils.c b/libavutil/parseutils.c
index 167e822648..fffe338f56 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][10] = {
     "january", "february", "march", "april", "may", "june", "july", "august",
     "september", "october", "november", "december"
 };
-- 
2.25.1