mirror of https://code.videolan.org/videolan/vlc
vlc_(d|l|m)rand48: thread-safe wrappers for non-secure/fast PRNG
These functions are just convenience so we don't need to seed the PRNG all the time, nor to use vlc_rand_bytes() for non-security-critical randomness.
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@ -29,4 +29,9 @@
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VLC_EXPORT( void, vlc_rand_bytes, (void *buf, size_t len) );
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/* Interlocked (but not reproducible) functions for the POSIX PRNG */
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VLC_EXPORT( double, vlc_drand48, (void) LIBVLC_USED );
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VLC_EXPORT( long, vlc_lrand48, (void) LIBVLC_USED );
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VLC_EXPORT( long, vlc_mrand48, (void) LIBVLC_USED );
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#endif
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@ -553,6 +553,9 @@ vlc_plugin_set
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vlc_poll
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vlc_tdestroy
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vlc_rand_bytes
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vlc_drand48
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vlc_lrand48
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vlc_mrand48
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vlc_release
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vlc_restorecancel
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vlc_rwlock_destroy
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@ -163,3 +163,82 @@ void vlc_rand_bytes (void *buf, size_t len)
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}
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}
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#endif
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static struct
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{
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bool init;
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unsigned short subi[3];
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vlc_mutex_t lock;
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} rand48 = { false, { 0, 0, 0, }, VLC_STATIC_MUTEX, };
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static void init_rand48 (void)
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{
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if (!rand48.init)
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{
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vlc_rand_bytes (rand48.subi, sizeof (rand48.subi));
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#if 0 // short would be more than 16-bits ?
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for (unsigned i = 0; i < 3; i++)
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subi[i] &= 0xffff;
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#endif
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}
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}
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/**
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* PRNG uniformly distributed between 0.0 and 1.0 with 48-bits precision.
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*
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* @note Contrary to POSIX drand48(), this function is thread-safe.
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* @warning Series generated by this function are not reproducible.
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* Use erand48() if you need reproducible series.
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*
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* @return a double value within [0.0, 1.0] inclusive
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*/
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double vlc_drand48 (void)
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{
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double ret;
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vlc_mutex_lock (&rand48.lock);
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init_rand48 ();
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ret = erand48 (rand48.subi);
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vlc_mutex_unlock (&rand48.lock);
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return ret;
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}
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/**
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* PRNG uniformly distributed between 0 and 2^32 - 1.
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*
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* @note Contrary to POSIX lrand48(), this function is thread-safe.
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* @warning Series generated by this function are not reproducible.
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* Use nrand48() if you need reproducible series.
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*
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* @return a double value within [0.0, 1.0] inclusive
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*/
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long vlc_lrand48 (void)
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{
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long ret;
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vlc_mutex_lock (&rand48.lock);
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init_rand48 ();
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ret = nrand48 (rand48.subi);
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vlc_mutex_unlock (&rand48.lock);
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return ret;
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}
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/**
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* PRNG uniformly distributed between -2^32 and 2^32 - 1.
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*
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* @note Contrary to POSIX mrand48(), this function is thread-safe.
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* @warning Series generated by this function are not reproducible.
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* Use jrand48() if you need reproducible series.
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*
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* @return a double value within [0.0, 1.0] inclusive
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*/
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long vlc_mrand48 (void)
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{
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long ret;
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vlc_mutex_lock (&rand48.lock);
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init_rand48 ();
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ret = jrand48 (rand48.subi);
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vlc_mutex_unlock (&rand48.lock);
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return ret;
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}
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