From 02ed1066ba50eb90e040eb7a1de047416700fb81 Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto@midokura.com>
Date: Fri, 23 Apr 2021 10:01:31 +0900
Subject: [PATCH 1/3] test_grouping: use unsigned variables where it makes more
 sense

---
 lib/identify.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/lib/identify.c b/lib/identify.c
index b725fea..b69f37f 100644
--- a/lib/identify.c
+++ b/lib/identify.c
@@ -380,7 +380,8 @@ static void record_capstone(struct quirc *q, int ring, int stone)
 	perspective_map(capstone->c, 3.5, 3.5, &capstone->center);
 }
 
-static void test_capstone(struct quirc *q, int x, int y, int *pb)
+static void test_capstone(struct quirc *q, unsigned int x, unsigned int y,
+			  unsigned int *pb)
 {
 	int ring_right = region_code(q, x - pb[4], y);
 	int stone = region_code(q, x - pb[4] - pb[3] - pb[2], y);
@@ -389,7 +390,7 @@ static void test_capstone(struct quirc *q, int x, int y, int *pb)
 				    y);
 	struct quirc_region *stone_reg;
 	struct quirc_region *ring_reg;
-	int ratio;
+	unsigned int ratio;
 
 	if (ring_left < 0 || ring_right < 0 || stone < 0)
 		return;
@@ -417,14 +418,14 @@ static void test_capstone(struct quirc *q, int x, int y, int *pb)
 	record_capstone(q, ring_left, stone);
 }
 
-static void finder_scan(struct quirc *q, int y)
+static void finder_scan(struct quirc *q, unsigned int y)
 {
 	quirc_pixel_t *row = q->pixels + y * q->w;
-	int x;
+	unsigned int x;
 	int last_color = 0;
-	int run_length = 0;
-	int run_count = 0;
-	int pb[5];
+	unsigned int run_length = 0;
+	unsigned int run_count = 0;
+	unsigned int pb[5];
 
 	memset(pb, 0, sizeof(pb));
 	for (x = 0; x < q->w; x++) {
@@ -437,9 +438,9 @@ static void finder_scan(struct quirc *q, int y)
 			run_count++;
 
 			if (!color && run_count >= 5) {
-				static int check[5] = {1, 1, 3, 1, 1};
-				int avg, err;
-				int i;
+				static unsigned int check[5] = {1, 1, 3, 1, 1};
+				unsigned int avg, err;
+				unsigned int i;
 				int ok = 1;
 
 				avg = (pb[0] + pb[1] + pb[3] + pb[4]) / 4;
@@ -1024,7 +1025,7 @@ static void test_neighbours(struct quirc *q, int i,
 	record_qr_grid(q, best_h, i, best_v);
 }
 
-static void test_grouping(struct quirc *q, int i)
+static void test_grouping(struct quirc *q, unsigned int i)
 {
 	struct quirc_capstone *c1 = &q->capstones[i];
 	int j;

From 734258c7755e56cbb185eaecf99d813109585175 Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto@midokura.com>
Date: Fri, 23 Apr 2021 10:03:00 +0900
Subject: [PATCH 2/3] finder_scan: constify the "check" array

---
 lib/identify.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/identify.c b/lib/identify.c
index b69f37f..bddd3c6 100644
--- a/lib/identify.c
+++ b/lib/identify.c
@@ -438,7 +438,7 @@ static void finder_scan(struct quirc *q, unsigned int y)
 			run_count++;
 
 			if (!color && run_count >= 5) {
-				static unsigned int check[5] = {1, 1, 3, 1, 1};
+				static const unsigned int check[5] = {1, 1, 3, 1, 1};
 				unsigned int avg, err;
 				unsigned int i;
 				int ok = 1;

From 65379a7c3966b202f3f223769652e6c01b7cd28e Mon Sep 17 00:00:00 2001
From: YAMAMOTO Takashi <yamamoto@midokura.com>
Date: Fri, 23 Apr 2021 10:06:50 +0900
Subject: [PATCH 3/3] finder_scan: Improve capstone detection on small images

When using small captured images, I somehow frequently see failures
to recognize a capstone due to rounding errors.
eg. when pb[] = {2 3 8 3 2}.

This commit tries to improve it by using fixed-point arithmetics.
The scaling factor was chosen somehow arbitrary. A moderate scaling
should be enough.
---
 lib/identify.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/identify.c b/lib/identify.c
index bddd3c6..7a1096e 100644
--- a/lib/identify.c
+++ b/lib/identify.c
@@ -438,17 +438,18 @@ static void finder_scan(struct quirc *q, unsigned int y)
 			run_count++;
 
 			if (!color && run_count >= 5) {
+				const int scale = 16;
 				static const unsigned int check[5] = {1, 1, 3, 1, 1};
 				unsigned int avg, err;
 				unsigned int i;
 				int ok = 1;
 
-				avg = (pb[0] + pb[1] + pb[3] + pb[4]) / 4;
+				avg = (pb[0] + pb[1] + pb[3] + pb[4]) * scale / 4;
 				err = avg * 3 / 4;
 
 				for (i = 0; i < 5; i++)
-					if (pb[i] < check[i] * avg - err ||
-					    pb[i] > check[i] * avg + err)
+					if (pb[i] * scale < check[i] * avg - err ||
+					    pb[i] * scale > check[i] * avg + err)
 						ok = 0;
 
 				if (ok)