[FFmpeg-devel] [PATCH] Improve documentation for libavutil/base64.h

[Michael Niedermayer]

On Sat, Feb 07, 2009 at 06:02:49PM +0100, Stefano Sabatini wrote:
> On date Saturday 2009-02-07 03:11:45 +0100, Michael Niedermayer encoded:
> > On Sat, Feb 07, 2009 at 01:27:15AM +0100, Stefano Sabatini wrote:
> > > On date Wednesday 2009-01-28 01:03:29 +0100, Stefano Sabatini encoded:
> > > [...]
> > > > Index: libavutil/base64.h
> > > > ===================================================================
> > > > --- libavutil/base64.h	(revision 16838)
> > > > +++ libavutil/base64.h	(working copy)
> > > > @@ -25,16 +25,29 @@
> > > >  #include <stdint.h>
> > > >  
> > > >  /**
> > > > - * decodes base64
> > > > - * param order as strncpy()
> > > > + * Decodes the base64-encoded string in \p src and puts the decoded
> > > > + * data in \p dst.
> > > > + *
> > > > + * @param dst_size size in bytes of the \p dst buffer, it should be at
> > > > + * least 3/4 of the length of \p src
> > > > + * @return the number of bytes written, or a negative value in case of
> > > > + * error
> > > >   */
> > > > -int av_base64_decode(uint8_t * out, const char *in, int out_length);
> > > > +int av_base64_decode(uint8_t *dst, const char *src, int dst_size);
> > > >  
> > > >  /**
> > > > - * encodes base64
> > > > - * @param src data, not a string
> > > > - * @param buf output string
> > > > + * Encodes in base64 the data in \p src and puts the resulting string
> > > > + * in \p dst.
> > > > + *
> > > > + * @param dst_size size in bytes of the \p dst string
> > > > + * @warning While the encoded string size is 4/3 * N + 1, N being the
> > > > + * smaller multiple of 3 greater than or equal to \p src_size, you may
> > > > + * need to overallocate by few bytes the \p dst buffer, or the
> > > > + * function may fail.
> > > > + * @param src_size size in bytes of the \p src buffer
> > > > + * @return the string containing the encoded data, or NULL in case of
> > > > + * error
> > > >   */
> > > > -char *av_base64_encode(char * buf, int buf_len, const uint8_t * src, int len);
> > > > +char *av_base64_encode(char *dst, int dst_size, const uint8_t *src, int src_size);
> > > >  
> > > >  #endif /* AVUTIL_BASE64_H */
> > > 
> > > Ping?
> > 
> > rejected :)
> > "While the encoded string size is 4/3 * N + 1, N being the
> > smaller multiple of 3 greater than or equal to \p src_size"
> > 
> > that be confusing
> > i dont remember exactly but possibly i suggested a clean variant already
> > somewhere in the thread but then maybe not ...
> 
> Well it was my fault to erroneosly infer that that variant was
> correct, it overallocates two bytes in the worst case.
> 
> Your variant: f(N) = floor(4 * (N+2) / 3)

my variant is
(len+2)/3*4+1
with c semantics of operations

if you want to proof it wrong the way to go is to provide a sequence
of bytes for which it is wrong not some obscure math that seems to
assert from the start that your claim is correct and that doesnt
even translate my variant correctly into your pseudo math

hint:
floor(4 * (3+2) / 3) = 6    (assuming real valued divide)
           (3+2)/3*4 = 4    (assuming integer round down divide)


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

Why not whip the teacher when the pupil misbehaves? -- Diogenes of Sinope
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