From 072850fb96ad71d8232d631c947dd069bb011298 Mon Sep 17 00:00:00 2001
From: Explorer09 <explorer09@gmail.com>
Date: Tue, 6 Feb 2024 23:15:52 +0800
Subject: [PATCH] findTopCellItem() handle underflow (f7)

---
 Meter.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/Meter.c b/Meter.c
index 4aabf1644..767cfcab2 100644
--- a/Meter.c
+++ b/Meter.c
@@ -386,9 +386,9 @@ static uint8_t GraphMeterMode_findTopCellItem(const Meter* this, double scaledTo
    assert(topCell < graphHeight);
 
    double valueSum = 0.0;
-   bool hasArea = false;
-   double maxValue = 0.0;
    uint8_t topCellItem = this->curItems - 1;
+   bool hasPrevArea = false;
+   double maxValue = 0.0;
    for (uint8_t i = 0; i < this->curItems && valueSum < DBL_MAX; i++) {
       double value = this->values[i];
       if (!isPositive(value))
@@ -412,38 +412,39 @@ static uint8_t GraphMeterMode_findTopCellItem(const Meter* this, double scaledTo
 
       double area = (value / scaledTotal) * (double)(int)graphHeight;
 
-      // if (maxValue <= 0.0)
-      // if (topCellItem >= i)
-      if (topCellItem > i) {
+      if (topCellItem >= i) {
+         assert(!hasPrevArea);
+         assert(maxValue <= 0.0);
+
          double topPoint = (valueSum / scaledTotal) * (double)(int)graphHeight;
          assert(topPoint >= 0.0);
 
          if (topCell > 0 && !(topPoint > (double)(int)topCell)) {
             continue;
          }
-         // If (topCell == 0), permit the cases where the division underflows
-         // (topPoint == 0.0).
+         // If (topCell == 0), permit the cases where the division underflows,
+         // i.e. "topPoint" and "area" both round to 0.0.
 
+         topCellItem = i;
          if (area > topPoint - (double)(int)topCell) {
-            hasArea = true;
-	    maxValue = topPoint - (double)(int)topCell;
+            hasPrevArea = true;
+            maxValue = topPoint - (double)(int)topCell;
          } else {
             maxValue = value;
-	 }
-         topCellItem = i;
+         }
       } else {
-         if (hasArea) {
+         if (hasPrevArea) {
             if (area >= maxValue) {
-               hasArea = false;
+               hasPrevArea = false;
                maxValue = value;
                topCellItem = i;
-	    }
+            }
          } else {
             if (value >= maxValue) {
                maxValue = value;
                topCellItem = i;
             }
-	 }
+         }
       }
    }
    return topCellItem;