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* [PATCH] readkey: shrink table of known escape sequences in size
@ 2020-09-14  9:59 Ahmad Fatoum
  2020-09-28  9:31 ` Sascha Hauer
  0 siblings, 1 reply; 7+ messages in thread
From: Ahmad Fatoum @ 2020-09-14  9:59 UTC (permalink / raw)
  To: barebox; +Cc: 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. Additionally, the nul byte need not be stored explicitly for
3-byte strings, if we know those are the largest strings we have.

The latter likely does not save us any space because of the usual
alignment rules, but it will allow us to support sequences one byte
bigger in future at no increase in size.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 lib/readkey.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/readkey.c b/lib/readkey.c
index c26e9d51aba9..551296de3eb6 100644
--- a/lib/readkey.c
+++ b/lib/readkey.c
@@ -20,8 +20,10 @@
 #include <linux/ctype.h>
 #include <readkey.h>
 
+#define MAX_ESC_LEN 3
+
 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


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^ permalink raw reply	[flat|nested] 7+ messages in thread
* [PATCH] readkey: shrink table of known escape sequences in size
@ 2020-09-28 12:39 Ahmad Fatoum
  2020-09-30  7:31 ` Sascha Hauer
  0 siblings, 1 reply; 7+ messages in thread
From: Ahmad Fatoum @ 2020-09-28 12:39 UTC (permalink / raw)
  To: barebox; +Cc: 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@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


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^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2020-09-30  7:31 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-14  9:59 [PATCH] readkey: shrink table of known escape sequences in size Ahmad Fatoum
2020-09-28  9:31 ` Sascha Hauer
2020-09-28 11:51   ` Ahmad Fatoum
2020-09-28 11:58     ` Sascha Hauer
2020-09-28 12:40       ` Ahmad Fatoum
2020-09-28 12:39 Ahmad Fatoum
2020-09-30  7:31 ` Sascha Hauer

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