[FFmpeg-devel] [PATCH] add put_bits_long to avoid undefined behaviour in put_bits

[Michael Niedermayer]

On Sat, Aug 22, 2009 at 10:22:19PM +0200, matthieu castet wrote:
> Hi,
>
> the put_bits can be called with
> 	unsigned int bit_buf = 0;
> 	int bit_left = 32;
> 	int n = 32;
> 	unsigned int value = 0x1ba;
>
> in the case of ALT_BITSTREAM_WRITER and BITSTREAM_WRITER_LE is not defined, 
> we
> will do "bit_buf<<=bit_left;"
> But sizeof(bit_buf) == 32 and bit_left==32, and we are in a undefined 
> behavior[1].
>
> This patch add a put_bits_long for n = 32 and restrict n <= 31 for 
> put_bits.
[..]
> @@ -259,6 +259,22 @@
>      put_bits(pb, bits, val & ((1<<bits)-1));
>  }
>  
> +static inline void put_bits_long(PutBitContext *s, int n, unsigned int value)
> +{
> +    if(n<=31) 
> +		put_bits(s, n, value);
> +    else{

should have {} for simplicity of future patches


> +#ifdef ALT_BITSTREAM_READER_LE
> +		put_bits(s, 16, value & 0xffff);
> +		put_bits(s, 16, value >> 16);
> +#else
> +		put_bits(s, 16, value >> 16);
> +		put_bits(s, 16, value & 0xffff);
> +#endif
> +    }
> +
> +}
> +
>  /**
>   * Returns the pointer to the byte where the bitstream writer will put
>   * the next bit.

tabs are forbidden in svn


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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