prng: fix rand() to give good sequence with small state

[musl] / src / prng / __rand48_step.c

#include <stdlib.h>
#include <inttypes.h>

uint64_t __rand48_step(unsigned short *xi, unsigned short *lc)
{
        uint64_t a, x;
        x = xi[0] | xi[1]<<16 | xi[2]+0ULL<<32;
        a = lc[0] | lc[1]<<16 | lc[2]+0ULL<<32;
        x = a*x + lc[3];
        xi[0] = x;
        xi[1] = x>>16;
        xi[2] = x>>32;
        return x & 0xffffffffffffull;
}