random.h File Reference

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Data Structures
struct	AVRandomState
Defines
#define	AV_RANDOM_N   624
Functions
void	av_init_random (unsigned int 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).
static unsigned int	av_random (AVRandomState *state)
static double	av_random_real1 (AVRandomState *state)
void	av_benchmark_random (void)

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Define Documentation

#define AV_RANDOM_N   624

Definition at line 27 of file random.h.

Referenced by av_init_random(), av_random(), and av_random_generate_untempered_numbers().

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Function Documentation

void av_benchmark_random

(

void

)

void av_init_random	(	unsigned int	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

initializes mt[AV_RANDOM_N] with a seed

Definition at line 46 of file random.c.

References AV_RANDOM_N, AVRandomState::index, and AVRandomState::mt.

Referenced by ac3_decode_init(), cook_decode_init(), decode_init(), main(), mpc7_decode_init(), mpc8_decode_init(), and roq_encode_init().

{
    int index;

    /*
     This differs from the wikipedia article.  Source is from the Makoto
     Makoto Matsumoto and Takuji Nishimura code, with the following comment:
     */
     /* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
     /* In the previous versions, MSBs of the seed affect   */
     /* only MSBs of the array mt[].                        */
    state->mt[0] = seed & 0xffffffff;
    for (index = 1; index < AV_RANDOM_N; index++) {
        unsigned int prev= state->mt[index - 1];
        state->mt[index] = (1812433253UL * (prev ^ (prev>>30)) + index) & 0xffffffff;
    }
    state->index= index; // will cause it to generate untempered numbers the first iteration
}

static unsigned int av_random

(

AVRandomState *

state

)

[inline, static]

generates a random number on [0,0xffffffff]-interval

Definition at line 39 of file random.h.

References av_random_generate_untempered_numbers(), AV_RANDOM_N, and AVRandomState::index.

Referenced by av_random_real1(), get_high_utility_cell(), get_transform_coeffs_ch(), http_parse_request(), idx_to_quant(), nelly_decode_block(), scalar_dequant_float(), and start_multicast().

{
    unsigned int y;

    // regenerate the untempered numbers if we should...
    if (state->index >= AV_RANDOM_N)
        av_random_generate_untempered_numbers(state);

    // grab one...
    y = state->mt[state->index++];

    /* Now temper (Mersenne Twister coefficients) The coefficients for MT19937 are.. */
    y ^= (y >> 11);
    y ^= (y << 7) & 0x9d2c5680;
    y ^= (y << 15) & 0xefc60000;
    y ^= (y >> 18);

    return y;
}

void av_random_generate_untempered_numbers

(

AVRandomState *

state

)

Regenerate the untempered numbers (must be done every 624 iterations, or it will loop).

generate AV_RANDOM_N words at one time (which will then be tempered later) (av_random calls this; you shouldn't)

Definition at line 66 of file random.c.

References A, AV_RANDOM_N, AVRandomState::index, LOWER_MASK, M, AVRandomState::mt, and UPPER_MASK.

Referenced by av_random().

{
    int kk;
    unsigned int y;

    for (kk = 0; kk < AV_RANDOM_N - M; kk++) {
        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
        state->mt[kk] = state->mt[kk + M] ^ (y >> 1) ^ ((y&1)*A);
    }
    for (; kk < AV_RANDOM_N - 1; kk++) {
        y = (state->mt[kk] & UPPER_MASK) | (state->mt[kk + 1] & LOWER_MASK);
        state->mt[kk] = state->mt[kk + (M - AV_RANDOM_N)] ^ (y >> 1) ^ ((y&1)*A);
    }
    y = (state->mt[AV_RANDOM_N - 1] & UPPER_MASK) | (state->mt[0] & LOWER_MASK);
    state->mt[AV_RANDOM_N - 1] = state->mt[M - 1] ^ (y >> 1) ^ ((y&1)*A);
    state->index = 0;
}

static double av_random_real1

(

AVRandomState *

state

)

[inline, static]

return random in range [0-1] as double

Definition at line 60 of file random.h.

References av_random().

{
    /* divided by 2^32-1 */
    return av_random(state) * (1.0 / 4294967296.0);
}

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