findTopCellItem() handle underflow (f3)

Meter.c

@@ -386,7 +386,8 @@ static uint8_t GraphMeterMode_findTopCellItem(const Meter* this, double scaledTo
    assert(topCell < graphHeight);
 
    double valueSum = 0.0;
-   double maxArea = 0.0;
+   bool hasArea = false;
+   double maxValue = 0.0;
    uint8_t topCellItem = this->curItems - 1;
    for (uint8_t i = 0; i < this->curItems && valueSum < DBL_MAX; i++) {
       double value = this->values[i];
@@ -406,26 +407,43 @@ static uint8_t GraphMeterMode_findTopCellItem(const Meter* this, double scaledTo
 
       valueSum = newValueSum;
 
-      double topPoint = (valueSum / scaledTotal) * (double)(int)graphHeight;
-      double area = (value / scaledTotal) * (double)(int)graphHeight;
+      // Find the item that occupies the largest area of the top cell.
+      // Favor item with higher index in case of a tie.
 
-      if (topPoint > (double)(int)topCell || (topPoint <= 0.0 && topCell < 1)) {
-         // If the division underflows (topPoint <= 0.0 && topCell < 1), that
-         // item still counts as part of the top cell ("area" would be 0.0 in
-         // this case).
+      // if (maxValue <= 0.0)
+      // if (topCellItem >= i)
+      if (topCellItem > i) {
+         double topPoint = (valueSum / scaledTotal) * (double)(int)graphHeight;
+         assert(topPoint >= 0.0);
 
-         // Cut the excess area
-         if (area > topPoint - (double)(int)topCell) {
-            area = topPoint - (double)(int)topCell;
+         if (topCell > 0 && !(topPoint > (double)(int)topCell)) {
+            continue;
          }
-         assert(area >= 0.0);
+         // If (topCell == 0), permit the cases where the division underflows
+         // (topPoint == 0.0).
 
-         // Find the item that occupies the largest area of the top cell.
-         // Favor item with higher index in case of a tie.
-         if (area >= maxArea) {
-            topCellItem = i;
-            maxArea = area;
-         }
+         double area = (value / scaledTotal) * (double)(int)graphHeight;
+         if (area > topPoint - (double)(int)topCell) {
+            hasArea = true;
+	    maxValue = topPoint - (double)(int)topCell;
+         } else {
+            maxValue = value;
+	 }
+         topCellItem = i;
+      } else {
+         if (hasArea) {
+            double area = (value / scaledTotal) * (double)(int)graphHeight;
+            if (area >= maxValue) {
+               hasArea = false;
+               maxValue = value;
+               topCellItem = i;
+	    }
+         } else {
+            if (value >= maxValue) {
+               maxValue = value;
+               topCellItem = i;
+            }
+	 }
       }
    }
    return topCellItem;