[Ffmpeg-devel] [RFC] av_random...

[Michael Niedermayer]

Hi

On Sun, Jan 07, 2007 at 08:08:01PM -0600, Ryan Martell wrote:
[...]
> >>
> >>typedef struct {
> >>    unsigned int magic_cookie; ///< prevent someone from calling
> >>random without the state setup (sets it up automatically)
> >>    unsigned long mt[AV_RANDOM_PERIOD];	///< the array for the state
> >>vector
> >>    int mti;
> >>} AVRandomState;
> >>
> >>void av_init_random(unsigned long seed, AVRandomState *state);
> >>
> >>unsigned long av_random(AVRandomState *state); // 32 bit random
> >>double av_random_real1(AVRandomState *state); // [0-1] as double
> >>
> >
> >>Or would you rather have:
> >>
> >>AVRandomState *av_init_random(unsigned long seed);
> >>void av_free_random(AVRandomState *state);
> >>
> >>unsigned long av_random(AVRandomState *state);
> >
> >this is closer to what i had in mind ...
> 
> Well, this doesn't make as much sense with the random being inlined,  
> since the AVRandomState would have to be visible for the inlining to  
> work.  In my mind, it would make sense for it to use a malloc/free if  
> the structure was opaque (in the c file), but not if it's in the h file.

ok


[...]

> #define AV_RANDOM_N 624
> #define AV_RANDOM_MAGIC_COOKIE 0xdeadbeef
> 
> typedef struct {
>     unsigned int magic_cookie; ///< prevent someone from calling random without the state setup

i dont like these magic_cookies, if someone calls the code without init then
thats pretty much his problem IMHO


>     unsigned long mt[AV_RANDOM_N];	///< the array for the state vector

unsigned int or uint_fast32_t if you want to be pedantic but long is
64-bit on some architectures and that is not really wanted here i think


>     int mti; ///< current untempered value we use as the base.
> } AVRandomState;
> 
> 
> void av_init_random(unsigned long seed, AVRandomState *state); ///< to be inlined, the struct must be visible, so it doesn't make sense to try and keep it opaque with malloc/free like calls
> void av_random_generate_untempered_numbers(AVRandomState *state); ///< Regenerate the untempered numbers (must be done every 624 iterations, or it will loop)
> 
> /* generates a random number on [0,0xffffffff]-interval */
> static inline unsigned int av_random(AVRandomState *state)

that should be /** ... */ for doxygen compatibility


> {
>     unsigned int y= 0;

y is not read before its written so the =0 is redundant


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Everything should be made as simple as possible, but not simpler.
-- Albert Einstein
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