On 14.12.2016 11:16, Moritz Barsnick wrote:
> On Wed, Dec 14, 2016 at 01:02:41 +0100, Andreas Cadhalpun wrote:
>> On 13.12.2016 08:11, Paul B Mahol wrote:
>>>> - st->codecpar->bit_rate = samplerate * framesize * 8 / 2048;
>>>> + st->codecpar->bit_rate = samplerate * framesize / 256;
>>
>> Why multiply with 8 when dividing by a multiple of 8 directly afterwards?
>> That's just a waste of computational resources.
>
> I can only explain the term with "readability" (e.g. "number of bytes
> times 8 is number of bits, divided by 2048 is the rate"). If you
> bracket the (8 / 2048), it would avoid the overflow, and the compiler
> should evaluate the term to that constant 256 anyway, right? (Just if
> anyone cares about the presumed readability.)
Well, (8 / 2048) = 0, but one can do "/ (2048 / 8)".
Attached is a version doing it that way. Do you think that's better?
Best regards,
Andreas
>From 6bf8af5e8db1986ec1e30143a088b91041eb9ead Mon Sep 17 00:00:00 2001
From: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
Date: Tue, 13 Dec 2016 00:35:12 +0100
Subject: [PATCH] omadec: fix overflows during bit rate calculation
Signed-off-by: Andreas Cadhalpun <andreas.cadhal...@googlemail.com>
---
libavformat/omadec.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libavformat/omadec.c b/libavformat/omadec.c
index 6e476db..757ae53 100644
--- a/libavformat/omadec.c
+++ b/libavformat/omadec.c
@@ -365,7 +365,7 @@ static int oma_read_header(AVFormatContext *s)
st->codecpar->channels = 2;
st->codecpar->channel_layout = AV_CH_LAYOUT_STEREO;
st->codecpar->sample_rate = samplerate;
- st->codecpar->bit_rate = st->codecpar->sample_rate * framesize * 8 / 1024;
+ st->codecpar->bit_rate = st->codecpar->sample_rate * framesize / (1024 / 8);
/* fake the ATRAC3 extradata
* (wav format, makes stream copy to wav work) */
@@ -398,7 +398,7 @@ static int oma_read_header(AVFormatContext *s)
return AVERROR_INVALIDDATA;
}
st->codecpar->sample_rate = samplerate;
- st->codecpar->bit_rate = samplerate * framesize * 8 / 2048;
+ st->codecpar->bit_rate = samplerate * framesize / (2048 / 8);
avpriv_set_pts_info(st, 64, 1, samplerate);
break;
case OMA_CODECID_MP3:
--
2.10.2
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