[PATCH] readkey: shrink table of known escape sequences in size

[Ahmad Fatoum]

Instead of storing pointers to 4-byte strings, we could just store the
characters directly in the struct. Can save us up to 18 pointers worth
of space.

We could save 18 x 1 byte more of static storage by making the strings
3 bytes of length as the nul byte need not be stored explicitly for
strings of maximal length.

For clarity, this optimization is omitted for now. We still use strncmp,
instead of strcmp use runs risk of accidental out of bounds reads when
longer escape sequences are added. This can't occur with strncmp.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
v1 -> v2:
  - Maintain a nul delimiter always at the cost of 18 more bytes
    (Sascha)
---
 lib/readkey.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/readkey.c b/lib/readkey.c
index c26e9d51aba9..6a4ddf14a99d 100644
--- a/lib/readkey.c
+++ b/lib/readkey.c
@@ -20,8 +20,10 @@
 #include <linux/ctype.h>
 #include <readkey.h>
 
+#define MAX_ESC_LEN 4
+
 struct esc_cmds {
-	const char *seq;
+	const char seq[MAX_ESC_LEN];
 	unsigned char val;
 };
 
@@ -49,7 +51,7 @@ static const struct esc_cmds esccmds[] = {
 int read_key(void)
 {
 	unsigned char c;
-	unsigned char esc[5];
+	unsigned char esc[MAX_ESC_LEN + 2];
 	c = getchar();
 
 	if (c == 27) {
@@ -67,7 +69,7 @@ int read_key(void)
 		}
 		esc[i] = 0;
 		for (i = 0; i < ARRAY_SIZE(esccmds); i++){
-			if (!strcmp(esc, esccmds[i].seq))
+			if (!strncmp(esc, esccmds[i].seq, MAX_ESC_LEN))
 				return esccmds[i].val;
 		}
 		return -1;
-- 
2.28.0