From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 1/4] avformat/mov_chan: check channel count at compile time by using a nonconst expression
Date: Mon, 1 Apr 2024 22:41:40 +0200
Message-ID: <GV1P250MB07373070C66D7FDF7F7EE8348F3F2@GV1P250MB0737.EURP250.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20240401185621.15297-1-cus@passwd.hu>
Marton Balint:
> If the channel tag does not match the number of channels, the constant
> expression evaluation should fail.
>
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
> libavformat/mov_chan.c | 48 +++++++++++++++++++-----------------------
> 1 file changed, 22 insertions(+), 26 deletions(-)
>
> diff --git a/libavformat/mov_chan.c b/libavformat/mov_chan.c
> index e7d181d71f..6ccc26b3f1 100644
> --- a/libavformat/mov_chan.c
> +++ b/libavformat/mov_chan.c
> @@ -81,24 +81,28 @@ struct MovChannelLayoutMap {
> };
> };
>
> -#define TAG(_0) {.tag = _0}
> -#define ID(_0) {.id = c_##_0}
> -#define CHLIST(_0, ...) TAG(_0), __VA_ARGS__
> -#define CHLIST01(_0, _1) CHLIST(_0, ID(_1))
> -#define CHLIST02(_0, _1, _2) CHLIST(_0, ID(_1), ID(_2))
> -#define CHLIST03(_0, _1, _2, _3) CHLIST(_0, ID(_1), ID(_2), ID(_3))
> -#define CHLIST04(_0, _1, _2, _3, _4) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4))
> -#define CHLIST05(_0, _1, _2, _3, _4, _5) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5))
> -#define CHLIST06(_0, _1, _2, _3, _4, _5, _6) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6))
> -#define CHLIST07(_0, _1, _2, _3, _4, _5, _6, _7) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7))
> -#define CHLIST08(_0, _1, _2, _3, _4, _5, _6, _7, _8) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8))
> -#define CHLIST09(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9) CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9))
> -#define CHLIST16(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16) \
> - CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9), ID(_10), \
> - ID(_11), ID(_12), ID(_13), ID(_14), ID(_15), ID(_16))
> -#define CHLIST21(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21) \
> - CHLIST(_0, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9), ID(_10), \
> - ID(_11), ID(_12), ID(_13), ID(_14), ID(_15), ID(_16), ID(_17), ID(_18), ID(_19), ID(_20), ID(_21))
> +static int nonconst_expr(void) {
> + return 0;
> +}
> +
> +#define TAG(_tag, _cnt) {.tag = (_tag & 0xffff) == _cnt ? _tag : nonconst_expr()}
> +#define ID(_0) {.id = c_##_0}
> +#define CHLIST(_tag, _cnt, ...) TAG(_tag, _cnt), __VA_ARGS__
> +#define CHLIST01(_tag, _1) CHLIST(_tag, 1, ID(_1))
> +#define CHLIST02(_tag, _1, _2) CHLIST(_tag, 2, ID(_1), ID(_2))
> +#define CHLIST03(_tag, _1, _2, _3) CHLIST(_tag, 3, ID(_1), ID(_2), ID(_3))
> +#define CHLIST04(_tag, _1, _2, _3, _4) CHLIST(_tag, 4, ID(_1), ID(_2), ID(_3), ID(_4))
> +#define CHLIST05(_tag, _1, _2, _3, _4, _5) CHLIST(_tag, 5, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5))
> +#define CHLIST06(_tag, _1, _2, _3, _4, _5, _6) CHLIST(_tag, 6, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6))
> +#define CHLIST07(_tag, _1, _2, _3, _4, _5, _6, _7) CHLIST(_tag, 7, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7))
> +#define CHLIST08(_tag, _1, _2, _3, _4, _5, _6, _7, _8) CHLIST(_tag, 8, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8))
> +#define CHLIST09(_tag, _1, _2, _3, _4, _5, _6, _7, _8, _9) CHLIST(_tag, 9, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9))
> +#define CHLIST16(_tag, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16) \
> + CHLIST(_tag, 16, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9), ID(_10), \
> + ID(_11), ID(_12), ID(_13), ID(_14), ID(_15), ID(_16))
> +#define CHLIST21(_tag, _1, _2, _3, _4, _5, _6, _7, _8, _9, _10, _11, _12, _13, _14, _15, _16, _17, _18, _19, _20, _21) \
> + CHLIST(_tag, 21, ID(_1), ID(_2), ID(_3), ID(_4), ID(_5), ID(_6), ID(_7), ID(_8), ID(_9), ID(_10), \
> + ID(_11), ID(_12), ID(_13), ID(_14), ID(_15), ID(_16), ID(_17), ID(_18), ID(_19), ID(_20), ID(_21))
>
> static const struct MovChannelLayoutMap mov_ch_layout_map[] = {
> CHLIST01( MOV_CH_LAYOUT_MONO, C ),
> @@ -281,14 +285,6 @@ static const struct {
>
> static const struct MovChannelLayoutMap* find_layout_map(uint32_t tag)
> {
> -#if defined(ASSERT_LEVEL) && ASSERT_LEVEL > 1
> - {
> - int i;
> - for (i = 0; i < FF_ARRAY_ELEMS(mov_ch_layout_map); i += 1 + (mov_ch_layout_map[i].tag & 0xffff))
> - av_assert2(mov_ch_layout_map[i].tag & 0xffff0000);
> - av_assert2(i == FF_ARRAY_ELEMS(mov_ch_layout_map));
> - }
> -#endif
> for (int i = 0; i < FF_ARRAY_ELEMS(mov_ch_layout_map); i += 1 + (mov_ch_layout_map[i].tag & 0xffff))
> if (mov_ch_layout_map[i].tag == tag)
> return &mov_ch_layout_map[i + 1];
When you want to check something at compile-time, wouldn't a
static_assert be the more appropriate tool? It allows to get nicer error
messages.
I see two ways how to use static_assert here (a) is preferred):
a) Turn the table used to initialize mov_ch_layout_map into an X-macro
and make TAG evaluate to static_assert((_tag & 0xffff) == _cnt, "Channel
count of " #_tag " wrong");} in one pass.
b) Shoehorn it into the TAG macro, e.g. like so:
#define CHECK_CONSISTENCY(_tag, _cnt) \
sizeof(struct {int a; static_assert((_tag & 0xffff) == _cnt, \
"Channel count of " #_tag " wrong");})
#define TAG(_tag, _cnt) {.tag =
CHECK_CONSISTENCY(_tag, (_cnt)) ? _tag : 0}
static_assert may only be used where a declaration can be used; we use
sizeof with a new struct type to circumvent this. This is legal C, but
unfortunately MSVC warns about it (although it accepts it).
- Andreas
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next prev parent reply other threads:[~2024-04-01 20:41 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-01 18:56 Marton Balint
2024-04-01 18:56 ` [FFmpeg-devel] [PATCH 2/4] avformat/mov_chan: factorize some layout map search functions Marton Balint
2024-04-01 18:56 ` [FFmpeg-devel] [PATCH 3/4] avformat/mov_chan: respect channel order when parsing and creating chnl atom Marton Balint
2024-04-01 19:37 ` James Almer
2024-04-01 20:43 ` Marton Balint
2024-04-01 18:56 ` [FFmpeg-devel] [PATCH 4/4] avformat/mov_chan: add support for omitted_channel bitmask in " Marton Balint
2024-04-01 20:41 ` Andreas Rheinhardt [this message]
2024-04-02 22:40 ` [FFmpeg-devel] [PATCH v2 1/4] avformat/mov_chan: check channel count of layout tags at compile time Marton Balint
2024-04-08 19:48 ` Marton Balint
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