#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)
unsigned short _rand48_seed[3] = {
RAND48_SEED_0,
RAND48_SEED_1,
RAND48_SEED_2
};
unsigned short _rand48_mult[3] = {
RAND48_MULT_0,
RAND48_MULT_1,
RAND48_MULT_2
};
unsigned short _rand48_add = RAND48_ADD;
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;
}
double erand48(unsigned short xseed[3])
{
_dorand48(xseed);
return ldexp((double) xseed[0], -48) +
ldexp((double) xseed[1], -32) +
ldexp((double) xseed[2], -16);
}
double drand48(){
return erand48(_rand48_seed);
}
void srand48(long seed){
_rand48_seed[0] = RAND48_SEED_0;
_rand48_seed[1] = (unsigned short)seed;
_rand48_seed[2] = (unsigned short)(seed >> 16);
_rand48_mult[0] = RAND48_MULT_0;
_rand48_mult[1] = RAND48_MULT_1;
_rand48_mult[2] = RAND48_MULT_2;
_rand48_add = RAND48_ADD;
}