HISTCOUNTER
p->lowpc = ROUNDDOWN(lowpc, HISTFRACTION * sizeof(HISTCOUNTER));
p->highpc = ROUNDUP(highpc, HISTFRACTION * sizeof(HISTCOUNTER));
lowpc = ROUNDDOWN(KERNBASE, HISTFRACTION * sizeof(HISTCOUNTER));
highpc = ROUNDUP((u_long)etext, HISTFRACTION * sizeof(HISTCOUNTER));
#define MAXARCS ((1 << (8 * sizeof(HISTCOUNTER))) - 2)