if (f->shlim && f->rend - f->rpos > f->shlim - f->shcnt - 1)
f->shend = f->rpos + (f->shlim - f->shcnt - 1);
else
f->shend = f->rend;
if (f->shlim && f->rend - f->rpos > f->shlim - f->shcnt - 1)
f->shend = f->rpos + (f->shlim - f->shcnt - 1);
else
f->shend = f->rend;