NBPDP
#define PDPMASK (NBPDP-1)
eva = sva + NBPDP; /* can overflow */
va_next = (sva + NBPDP) & ~PDPMASK;
*pva = (va & ~(long)(NBPDP - 1)) + NBPDP;
*pva = (va & ~(long)(NBPDP - 1)) + NBPDP;
ndmpdp = (ptoa(Maxmem) + NBPDP - 1) >> PDPSHIFT;
va_next = (sva + NBPDP) & ~PDPMASK;
va_next = (sva + NBPDP) & ~PDPMASK;
va = (va & ~(long)(NBPDP - 1)) + NBPDP;
va_next = (sva + NBPDP) & ~PDPMASK;