From de68db7b690719fc780fcb8308c5715267e67ed6 Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto@midokura.com>
Date: Thu, 8 Apr 2021 13:24:32 +0900
Subject: [PATCH 1/2] otsu: Use double for weighted sums

My phone camera produces 12M-pixel images.
They can easily overflow an int.
---
 lib/identify.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/identify.c b/lib/identify.c
index b725fea..584994f 100644
--- a/lib/identify.c
+++ b/lib/identify.c
@@ -190,14 +190,14 @@ static uint8_t otsu(const struct quirc *q)
 	}
 
 	// Calculate weighted sum of histogram values
-	unsigned int sum = 0;
+	double sum = 0;
 	unsigned int i = 0;
 	for (i = 0; i <= UINT8_MAX; ++i) {
 		sum += i * histogram[i];
 	}
 
 	// Compute threshold
-	int sumB = 0;
+	double sumB = 0;
 	int q1 = 0;
 	double max = 0;
 	uint8_t threshold = 0;
@@ -213,8 +213,8 @@ static uint8_t otsu(const struct quirc *q)
 			break;
 
 		sumB += i * histogram[i];
-		const double m1 = (double)sumB / q1;
-		const double m2 = ((double)sum - sumB) / q2;
+		const double m1 = sumB / q1;
+		const double m2 = (sum - sumB) / q2;
 		const double m1m2 = m1 - m2;
 		const double variance = m1m2 * m1m2 * q1 * q2;
 		if (variance >= max) {

From ea9b6ee5efbcff60b2737dd1378b3dbf22c6f93c Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto@midokura.com>
Date: Thu, 8 Apr 2021 13:35:12 +0900
Subject: [PATCH 2/2] otsu: Use unsigned for the pixel numbers

Because singed numbers don't make sense here.
---
 lib/identify.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/identify.c b/lib/identify.c
index 584994f..5c66865 100644
--- a/lib/identify.c
+++ b/lib/identify.c
@@ -177,13 +177,13 @@ static void flood_fill_seed(struct quirc *q, int x, int y, int from, int to,
 
 static uint8_t otsu(const struct quirc *q)
 {
-	int numPixels = q->w * q->h;
+	unsigned int numPixels = q->w * q->h;
 
 	// Calculate histogram
 	unsigned int histogram[UINT8_MAX + 1];
 	(void)memset(histogram, 0, sizeof(histogram));
 	uint8_t* ptr = q->image;
-	int length = numPixels;
+	unsigned int length = numPixels;
 	while (length--) {
 		uint8_t value = *ptr++;
 		histogram[value]++;
@@ -198,7 +198,7 @@ static uint8_t otsu(const struct quirc *q)
 
 	// Compute threshold
 	double sumB = 0;
-	int q1 = 0;
+	unsigned int q1 = 0;
 	double max = 0;
 	uint8_t threshold = 0;
 	for (i = 0; i <= UINT8_MAX; ++i) {
@@ -208,7 +208,7 @@ static uint8_t otsu(const struct quirc *q)
 			continue;
 
 		// Weighted foreground
-		const int q2 = numPixels - q1;
+		const unsigned int q2 = numPixels - q1;
 		if (q2 == 0)
 			break;