/*-------------------------------------------------------------------------

 *

 * pseudorandomfuncs.c

 *    Functions giving SQL access to a pseudorandom number generator.

 *

 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group

 * Portions Copyright (c) 1994, Regents of the University of California

 *

 * IDENTIFICATION

 *    src/backend/utils/adt/pseudorandomfuncs.c

 *

 *-------------------------------------------------------------------------

 */

#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"

/* Shared PRNG state used by all the random functions */

static pg_prng_state prng_state;

static bool prng_seed_set = false;

/*

 * initialize_prng() -

 *

 *  Initialize (seed) the PRNG, if not done yet in this process.

 */

static void

initialize_prng(void)

{

  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;

  }

}

/*

 * setseed() -

 *

 *  Seed the PRNG from a specified value in the range [-1.0, 1.0].

 */

Datum

setseed(PG_FUNCTION_ARGS)

{

  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();

}

/*

 * drandom() -

 *

 *  Returns a random number chosen uniformly in the range [0.0, 1.0).

 */

Datum

drandom(PG_FUNCTION_ARGS)

{

  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);

}

/*

 * drandom_normal() -

 *

 *  Returns a random number from a normal distribution.

 */

Datum

drandom_normal(PG_FUNCTION_ARGS)

{

  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);

}

/*

 * int4random() -

 *

 *  Returns a random 32-bit integer chosen uniformly in the specified range.

 */

Datum

int4random(PG_FUNCTION_ARGS)

{

  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);

}

/*

 * int8random() -

 *

 *  Returns a random 64-bit integer chosen uniformly in the specified range.

 */

Datum

int8random(PG_FUNCTION_ARGS)

{

  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);

}

/*

 * numeric_random() -

 *

 *  Returns a random numeric value chosen uniformly in the specified range.

 */

Datum

numeric_random(PG_FUNCTION_ARGS)

{

  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);

}