linux-kernel - [PATCH v2] vt: Use bsearch library function in is_double

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Message-Id: <20170831142115.28098-1-thomas@m3y3r.de>
Date:   Thu, 31 Aug 2017 16:21:15 +0200
From:   Thomas Meyer <thomas@...3r.de>
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Cc:     Thomas Meyer <thomas@...3r.de>
Subject: [PATCH v2] vt: Use bsearch library function in is_double_width

Use bsearch library function instead of duplicated functionality.

v2: Re-introduce early exit from old binary search.

Signed-off-by: Thomas Meyer <thomas@...3r.de>
---
 drivers/tty/vt/vt.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 2ebaba16f785..ca55004a639e 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -102,6 +102,7 @@
 #include <linux/uaccess.h>
 #include <linux/kdb.h>
 #include <linux/ctype.h>
+#include <linux/bsearch.h>
 
 #define MAX_NR_CON_DRIVER 16
 
@@ -2142,22 +2143,15 @@ struct interval {
 	uint32_t last;
 };
 
-static int bisearch(uint32_t ucs, const struct interval *table, int max)
+static int ucs_cmp(const void *key, const void *elt)
 {
-	int min = 0;
-	int mid;
+	uint32_t ucs = *(uint32_t *)key;
+	struct interval e = *(struct interval *) elt;
 
-	if (ucs < table[0].first || ucs > table[max].last)
-		return 0;
-	while (max >= min) {
-		mid = (min + max) / 2;
-		if (ucs > table[mid].last)
-			min = mid + 1;
-		else if (ucs < table[mid].first)
-			max = mid - 1;
-		else
-			return 1;
-	}
+	if (ucs > e.last)
+		return 1;
+	else if (ucs < e.first)
+		return -1;
 	return 0;
 }
 
@@ -2169,7 +2163,12 @@ static int is_double_width(uint32_t ucs)
 		{ 0xFE10, 0xFE19 }, { 0xFE30, 0xFE6F }, { 0xFF00, 0xFF60 },
 		{ 0xFFE0, 0xFFE6 }, { 0x20000, 0x2FFFD }, { 0x30000, 0x3FFFD }
 	};
-	return bisearch(ucs, double_width, ARRAY_SIZE(double_width) - 1);
+	if (ucs < double_width[0].first ||
+	    ucs > double_width[ARRAY_SIZE(double_width) - 1].last)
+		return 0;
+
+	return bsearch(&ucs, double_width, ARRAY_SIZE(double_width),
+			sizeof(struct interval), ucs_cmp) != NULL;
 }
 
 static void con_flush(struct vc_data *vc, unsigned long draw_from,
-- 
2.11.0