m := &cmerge.Merger{}
	err := m.SetModeAndGranularity("mdf1.data", coverage.CtrModeSet, coverage.CtrGranularityPerBlock)
	if err != nil {
		t.Fatalf("unexpected clash: %v", err)
	}
	err = m.SetModeAndGranularity("mdf1.data", coverage.CtrModeSet, coverage.CtrGranularityPerBlock)
	if err != nil {
		t.Fatalf("unexpected clash: %v", err)
	}

	}
	return uint32(sum), overflow
}

// SetModeAndGranularity records the counter mode and granularity for
// the current merge. In the specific case of merging across coverage
// data files from different binaries, where we're combining data from
// more than one meta-data file, we need to check for and resolve
// mode/granularity clashes.

		return fmt.Errorf("internal error: counter mode clash: %q from test harness, %q from data file %s", ts.cmode.String(), newmode.String(), p.MetaFile)
	}
	newgran := mfr.CounterGranularity()
	if err := ts.cm.SetModeAndGranularity(p.MetaFile, cmode, newgran); err != nil {
		return err
	}

	// A map to store counter data, indexed by pkgid/fnid tuple.
	pmm := make(map[pkfunc][]uint32)

	// Helper to read a single counter data file.

func (d *dstate) EndCounters() {
}

func (d *dstate) VisitMetaDataFile(mdf string, mfr *decodemeta.CoverageMetaFileReader) {
	newgran := mfr.CounterGranularity()
	newmode := mfr.CounterMode()
	if err := d.cm.SetModeAndGranularity(mdf, newmode, newgran); err != nil {
		fatal("%v", err)
	}
	if d.cmd == debugDumpMode {
		fmt.Printf("Cover mode: %s\n", newmode.String())
		fmt.Printf("Cover granularity: %s\n", newgran.String())
	}

	// Record file hash.
	mm.pod.fileHash = mfr.FileHash()
	// Counter mode and granularity -- detect and record clashes here.
	newgran := mfr.CounterGranularity()
	newmode := mfr.CounterMode()
	if err := mm.SetModeAndGranularity(mdf, newmode, newgran); err != nil {
		fatal("%v", err)
	}
}

func (mm *metaMerge) beginCounterDataFile(cdr *decodecounter.CounterDataReader) {
	state := argvalues{
		osargs: cdr.OsArgs(),