linux-kernel - [PATCH 01/22] tty: vt: make rgb_from

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Date: Fri,  2 Feb 2024 07:55:47 +0100
From: "Jiri Slaby (SUSE)" <jirislaby@...nel.org>
To: gregkh@...uxfoundation.org
Cc: linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Jiri Slaby (SUSE)" <jirislaby@...nel.org>
Subject: [PATCH 01/22] tty: vt: make rgb_from_256() slighly more comprehensible

* make the parameter unsigned, as it is expected to be unsigned,
* make the computation easier to follow -- step-by-step, and
* don't use 85 / 2 which is only a reduced form of 255 / 6 (by a factor
  3). Unlike the former, the latter can be understood.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@...nel.org>
---
 drivers/tty/vt/vt.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 65cd40cac96b..7d42f148559a 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1588,7 +1588,7 @@ static void default_attr(struct vc_data *vc)
 
 struct rgb { u8 r; u8 g; u8 b; };
 
-static void rgb_from_256(int i, struct rgb *c)
+static void rgb_from_256(unsigned int i, struct rgb *c)
 {
 	if (i < 8) {            /* Standard colours. */
 		c->r = i&1 ? 0xaa : 0x00;
@@ -1599,9 +1599,12 @@ static void rgb_from_256(int i, struct rgb *c)
 		c->g = i&2 ? 0xff : 0x55;
 		c->b = i&4 ? 0xff : 0x55;
 	} else if (i < 232) {   /* 6x6x6 colour cube. */
-		c->r = (i - 16) / 36 * 85 / 2;
-		c->g = (i - 16) / 6 % 6 * 85 / 2;
-		c->b = (i - 16) % 6 * 85 / 2;
+		i -= 16;
+		c->b = i % 6 * 255 / 6;
+		i /= 6;
+		c->g = i % 6 * 255 / 6;
+		i /= 6;
+		c->r = i     * 255 / 6;
 	} else                  /* Grayscale ramp. */
 		c->r = c->g = c->b = i * 10 - 2312;
 }
-- 
2.43.0