#include "postgres.h"
#include <math.h>
#include "common/pg_prng.h"
#include "miscadmin.h"
#include "utils/fmgrprotos.h"
#include "utils/numeric.h"
#include "utils/timestamp.h"

Include dependency graph for pseudorandomfuncs.c:

Functions
static void	initialize_prng (void)

Datum	setseed (PG_FUNCTION_ARGS)

Datum	drandom (PG_FUNCTION_ARGS)

Datum	drandom_normal (PG_FUNCTION_ARGS)

Datum	int4random (PG_FUNCTION_ARGS)

Datum	int8random (PG_FUNCTION_ARGS)

Datum	numeric_random (PG_FUNCTION_ARGS)

Variables
static pg_prng_state	prng_state

static bool	prng_seed_set = false

Function Documentation

◆ drandom()

Datum drandom ( PG_FUNCTION_ARGS )

Definition at line 84 of file pseudorandomfuncs.c.

{
    float8      result;
 
    initialize_prng();
 
    /* pg_prng_double produces desired result range [0.0, 1.0) */
    result = pg_prng_double(&prng_state);
 
    PG_RETURN_FLOAT8(result);
}

References initialize_prng(), pg_prng_double(), PG_RETURN_FLOAT8, and prng_state.

◆ drandom_normal()

Datum drandom_normal ( PG_FUNCTION_ARGS )

Definition at line 102 of file pseudorandomfuncs.c.

{
    float8      mean = PG_GETARG_FLOAT8(0);
    float8      stddev = PG_GETARG_FLOAT8(1);
    float8      result,
                z;
 
    initialize_prng();
 
    /* Get random value from standard normal(mean = 0.0, stddev = 1.0) */
    z = pg_prng_double_normal(&prng_state);
    /* Transform the normal standard variable (z) */
    /* using the target normal distribution parameters */
    result = (stddev * z) + mean;
 
    PG_RETURN_FLOAT8(result);
}

References initialize_prng(), PG_GETARG_FLOAT8, pg_prng_double_normal(), PG_RETURN_FLOAT8, and prng_state.

◆ initialize_prng()

static void initialize_prng ( void )

static

Definition at line 34 of file pseudorandomfuncs.c.

{
    if (unlikely(!prng_seed_set))
    {
        /*
         * If possible, seed the PRNG using high-quality random bits. Should
         * that fail for some reason, we fall back on a lower-quality seed
         * based on current time and PID.
         */
        if (unlikely(!pg_prng_strong_seed(&prng_state)))
        {
            TimestampTz now = GetCurrentTimestamp();
            uint64      iseed;
 
            /* Mix the PID with the most predictable bits of the timestamp */
            iseed = (uint64) now ^ ((uint64) MyProcPid << 32);
            pg_prng_seed(&prng_state, iseed);
        }
        prng_seed_set = true;
    }
}

References GetCurrentTimestamp(), MyProcPid, now(), pg_prng_seed(), pg_prng_strong_seed, prng_seed_set, prng_state, and unlikely.

Referenced by drandom(), drandom_normal(), int4random(), int8random(), and numeric_random().

◆ int4random()

Datum int4random ( PG_FUNCTION_ARGS )

Definition at line 126 of file pseudorandomfuncs.c.

{
    int32       rmin = PG_GETARG_INT32(0);
    int32       rmax = PG_GETARG_INT32(1);
    int32       result;
 
    if (rmin > rmax)
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("lower bound must be less than or equal to upper bound"));
 
    initialize_prng();
 
    result = (int32) pg_prng_int64_range(&prng_state, rmin, rmax);
 
    PG_RETURN_INT32(result);
}

References ereport, errcode(), errmsg(), ERROR, initialize_prng(), PG_GETARG_INT32, pg_prng_int64_range(), PG_RETURN_INT32, and prng_state.

◆ int8random()

Datum int8random ( PG_FUNCTION_ARGS )

Definition at line 150 of file pseudorandomfuncs.c.

{
    int64       rmin = PG_GETARG_INT64(0);
    int64       rmax = PG_GETARG_INT64(1);
    int64       result;
 
    if (rmin > rmax)
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("lower bound must be less than or equal to upper bound"));
 
    initialize_prng();
 
    result = pg_prng_int64_range(&prng_state, rmin, rmax);
 
    PG_RETURN_INT64(result);
}

References ereport, errcode(), errmsg(), ERROR, initialize_prng(), PG_GETARG_INT64, pg_prng_int64_range(), PG_RETURN_INT64, and prng_state.

◆ numeric_random()

Datum numeric_random ( PG_FUNCTION_ARGS )

Definition at line 174 of file pseudorandomfuncs.c.

{
    Numeric     rmin = PG_GETARG_NUMERIC(0);
    Numeric     rmax = PG_GETARG_NUMERIC(1);
    Numeric     result;
 
    initialize_prng();
 
    result = random_numeric(&prng_state, rmin, rmax);
 
    PG_RETURN_NUMERIC(result);
}

References initialize_prng(), PG_GETARG_NUMERIC, PG_RETURN_NUMERIC, prng_state, and random_numeric().

◆ setseed()

Datum setseed ( PG_FUNCTION_ARGS )

Definition at line 62 of file pseudorandomfuncs.c.

{
    float8      seed = PG_GETARG_FLOAT8(0);
 
    if (seed < -1 || seed > 1 || isnan(seed))
        ereport(ERROR,
                errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                errmsg("setseed parameter %g is out of allowed range [-1,1]",
                       seed));
 
    pg_prng_fseed(&prng_state, seed);
    prng_seed_set = true;
 
    PG_RETURN_VOID();
}