test_pg_erand48.c

// pg erand48 implementation
#include <stdio.h>

#define RAND48_SEED_0   (0x330e)
#define RAND48_SEED_1   (0xabcd)
#define RAND48_SEED_2   (0x1234)
#define RAND48_MULT_0   (0xe66d)
#define RAND48_MULT_1   (0xdeec)
#define RAND48_MULT_2   (0x0005)
#define RAND48_ADD              (0x000b)

static unsigned short _rand48_seed[3] = {
        RAND48_SEED_0,
        RAND48_SEED_1,
        RAND48_SEED_2
};
static unsigned short _rand48_mult[3] = {
        RAND48_MULT_0,
        RAND48_MULT_1,
        RAND48_MULT_2
};
static unsigned short _rand48_add = RAND48_ADD;

static void
_dorand48(unsigned short xseed[3])
{
  unsigned long accu;
  unsigned short temp[2];

  accu = (unsigned long) _rand48_mult[0] * (unsigned long) xseed[0] +
    (unsigned long) _rand48_add;
  temp[0] = (unsigned short) accu;        /* lower 16 bits */
  accu >>= sizeof(unsigned short) * 8;
  accu += (unsigned long) _rand48_mult[0] * (unsigned long) xseed[1] +
    (unsigned long) _rand48_mult[1] * (unsigned long) xseed[0];
  temp[1] = (unsigned short) accu;        /* middle 16 bits */
  accu >>= sizeof(unsigned short) * 8;
  accu += _rand48_mult[0] * xseed[2] + _rand48_mult[1] * xseed[1] + _rand48_mult[2] * xseed[0];
  xseed[0] = temp[0];
  xseed[1] = temp[1];
  xseed[2] = (unsigned short) accu;
}

long
pg_lrand48(void)
{
  _dorand48(_rand48_seed);
  return ((long) _rand48_seed[2] << 15) + ((long) _rand48_seed[1] >> 1);
}

int main(void)
{
  long l;
  for (int i = 0; i < 1000000000; i++)
    l = pg_lrand48();

  fprintf(stdout, "%ld\n", l);
  return 0;
}