[FFmpeg-devel] [PATCH] Issue 636 : ALAC encoding sometimes fails
Fri Dec 5 15:12:34 CET 2008
Michael Niedermayer wrote:
> On Fri, Dec 05, 2008 at 10:09:16AM +0530, Jai Menon wrote:
>> Attached patch fixes issue 636 and a few other fringe cases where the
>> alac encoder produces
>> lossy output. I'm behind a NAT and svn doesn't work, so could someone
>> please apply. Thanks.
>> Index: libavcodec/alacenc.c
>> --- libavcodec/alacenc.c (revision 15797)
>> +++ libavcodec/alacenc.c (working copy)
>> @@ -253,7 +253,8 @@
>> sum >>= lpc.lpc_quant;
>> sum += samples;
>> - residual[i] = samples[lpc.lpc_order+1] - sum;
>> + residual[i] = (samples[lpc.lpc_order+1] - sum) << (32 -
>> + (32 - s->write_sample_size);
>> res_val = residual[i];
> you are missing a int32_t cast in there, without it this wont work on
> systems where int is not exactly 32bit
Alternatively substitute 8*sizeof(int) for 32. For maximum portability,
use CHAR_BIT rather than 8.
I assume the intent here is to sign-extend a smaller value to 32 bits.
Are compilers clever enough to realise this and use more efficient
methods where available? If not, we should add a macro or inline
function doing it properly.
mans at mansr.com
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