linux-kernel - [PATCH] HID: simplify code in fetch

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Message-ID: <ZvwYbESMZ667QZqY@google.com>
Date: Tue, 1 Oct 2024 08:42:36 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Jiri Kosina <jikos@...nel.org>, Benjamin Tissoires <bentiss@...nel.org>
Cc: linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] HID: simplify code in fetch_item()

We can easily calculate the size of the item using arithmetic (shifts).
This allows to pull duplicated code out of the switch statement, making
it cleaner.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
 drivers/hid/hid-core.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 988d0acbdf04..00942d40fe08 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -754,35 +754,32 @@ static u8 *fetch_item(__u8 *start, __u8 *end, struct hid_item *item)
 	}
 
 	item->format = HID_ITEM_FORMAT_SHORT;
-	item->size = b & 3;
+	item->size = BIT(b & 3) >> 1; /* 0, 1, 2, 3 -> 0, 1, 2, 4 */
+
+	if (end - start < item->size)
+		return NULL;
 
 	switch (item->size) {
 	case 0:
-		return start;
+		break;
 
 	case 1:
-		if ((end - start) < 1)
-			return NULL;
-		item->data.u8 = *start++;
-		return start;
+		item->data.u8 = *start;
+		break;
 
 	case 2:
-		if ((end - start) < 2)
-			return NULL;
 		item->data.u16 = get_unaligned_le16(start);
-		start = (__u8 *)((__le16 *)start + 1);
-		return start;
+		break;
 
-	case 3:
-		item->size++;
-		if ((end - start) < 4)
-			return NULL;
+	case 4:
 		item->data.u32 = get_unaligned_le32(start);
-		start = (__u8 *)((__le32 *)start + 1);
-		return start;
+		break;
+
+	default:
+		unreachable();
 	}
 
-	return NULL;
+	return start + item->size;
 }
 
 static void hid_scan_input_usage(struct hid_parser *parser, u32 usage)
-- 
2.46.1.824.gd892dcdcdd-goog


-- 
Dmitry