Confused with pointer arithmetic

Can anyone help me understand what these two lines are doing

buf = (char *)(malloc(2 * pagesize) & pagemask);
buf = (char *)(((long)buf + pagesize) & ∼pagemask);

I understand malloc but not sure what the & operation is trying to achieve in both expressions

Pagesize and pagemask are defined as follows earlier

pagesize = sysconf(_SC_PAGESIZE);
pagemask = pagesize - 1;

Thanks!

Edit1

This code is from a book "Unix FileSystems" by Steve D. Pate

Edit2

This is the full code

#include <sys/unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include “sys/fs/vx_ioctl.h”

#define MB (1024 * 1024)

main(int argc, char argv[])
{
    char        *buf;
    int         i, fd, advisory;
    long        pagesize, pagemask;

    if (argc != 2) {
        exit(1);
    }
    if (strcmp(argv[1], “VX_SEQ”) == 0) {
        advisory = VX_SEQ;
    } else if (strcmp(argv[1], “VX_RANDOM”) == 0) {
        advisory = VX_RANDOM;
    } else if (strcmp(argv[1], “VX_DIRECT”) == 0) {
        advisory = VX_DIRECT;
    }
    pagesize = sysconf(_SC_PAGESIZE);
    pagemask = pagesize - 1;
    buf = (char *)(malloc(2 * pagesize) & pagemask);
    buf = (char *)(((long)buf + pagesize) & ∼pagemask);

    fd = open(“myfile”, O_RDWR);
    ioctl(fd, VX_SETCACHE, advisory);
    for (i=0 ; i<MB ; i++) {
         read(fd, buf, 4096);
    }
}