move requiredDepth calculation after min/max ranges are checked

Without this, a data set with a ludicrously large value in it
could break a BSI field's depth even though the import would then
reject it.

always treat BSI fields as having at least their depth:

If you imported only small values, BSI fields could end up
not bothering to clear higher bits in existing values, which
produced strange behaviors.

Author: travisturner

field.go

@@ -1269,23 +1269,45 @@ func (f *Field) importValue(columnIDs []uint64, values []int64, options *ImportO
 		return errors.Wrap(ErrBSIGroupNotFound, f.name)
 	}
 
-	// Find the lowest/highest values.
+	// We want to determine the required bit depth, in case the field doesn't
+	// have as many bits currently as would be needed to represent these values,
+	// but only if the values are in-range for the field.
 	var min, max int64
-	for i, value := range values {
-		if i == 0 || value < min {
-			min = value
+	if len(values) > 0 {
+		min, max = values[0], values[0]
+	}
+
+	// Split import data by fragment.
+	dataByFragment := make(map[importKey]importValueData)
+	for i := range columnIDs {
+		columnID, value := columnIDs[i], values[i]
+		if value > bsig.Max {
+			return fmt.Errorf("%v, columnID=%v, value=%v", ErrBSIGroupValueTooHigh, columnID, value)
+		} else if value < bsig.Min {
+			return fmt.Errorf("%v, columnID=%v, value=%v", ErrBSIGroupValueTooLow, columnID, value)
 		}
-		if i == 0 || value > max {
+		if value > max {
 			max = value
 		}
+		if value < min {
+			min = value
+		}
+
+		// Attach value to each bsiGroup view.
+		for _, name := range []string{viewName} {
+			key := importKey{View: name, Shard: columnID / ShardWidth}
+			data := dataByFragment[key]
+			data.ColumnIDs = append(data.ColumnIDs, columnID)
+			data.Values = append(data.Values, value)
+			dataByFragment[key] = data
+		}
 	}
 
 	// Determine the highest bit depth required by the min & max.
 	requiredDepth := bitDepthInt64(min - bsig.Base)
 	if v := bitDepthInt64(max - bsig.Base); v > requiredDepth {
 		requiredDepth = v
 	}
-
 	// Increase bit depth if required.
 	if requiredDepth > bsig.BitDepth {
 		if err := func() error {
@@ -1297,26 +1319,8 @@ func (f *Field) importValue(columnIDs []uint64, values []int64, options *ImportO
 		}(); err != nil {
 			return errors.Wrap(err, "increasing bsi bit depth")
 		}
-	}
-
-	// Split import data by fragment.
-	dataByFragment := make(map[importKey]importValueData)
-	for i := range columnIDs {
-		columnID, value := columnIDs[i], values[i]
-		if value > bsig.Max {
-			return fmt.Errorf("%v, columnID=%v, value=%v", ErrBSIGroupValueTooHigh, columnID, value)
-		} else if value < bsig.Min {
-			return fmt.Errorf("%v, columnID=%v, value=%v", ErrBSIGroupValueTooLow, columnID, value)
-		}
-
-		// Attach value to each bsiGroup view.
-		for _, name := range []string{viewName} {
-			key := importKey{View: name, Shard: columnID / ShardWidth}
-			data := dataByFragment[key]
-			data.ColumnIDs = append(data.ColumnIDs, columnID)
-			data.Values = append(data.Values, value)
-			dataByFragment[key] = data
-		}
+	} else {
+		requiredDepth = bsig.BitDepth
 	}
 
 	// Import into each fragment.