fix signed range problems with hex conversions

torvalds · Junio C Hamano · commit 192a6be2a77a · 2007-05-30T15:01:37.000-07:00
Make hexval_table[] "const".  Also make sure that the accessor
function hexval() does not access the table with out-of-range
values by declaring its parameter "unsigned char", instead of
"unsigned int".

With this, gcc can just generate:

	movzbl  (%rdi), %eax
	movsbl  hexval_table(%rax),%edx
	movzbl  1(%rdi), %eax
	movsbl  hexval_table(%rax),%eax
	sall    $4, %edx
	orl     %eax, %edx

for the code to generate a byte from two hex characters.

Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Signed-off-by: Junio C Hamano &lt;junkio@cox.net&gt;
diff --git a/cache.h b/cache.h
@@ -302,8 +302,8 @@ extern int legacy_loose_object(unsigned char *);
 extern int has_pack_file(const unsigned char *sha1);
 extern int has_pack_index(const unsigned char *sha1);
 
-extern signed char hexval_table[256];
-static inline unsigned int hexval(unsigned int c)
+extern const signed char hexval_table[256];
+static inline unsigned int hexval(unsigned char c)
 {
 	return hexval_table[c];
 }
diff --git a/sha1_file.c b/sha1_file.c
@@ -32,7 +32,7 @@ const unsigned char null_sha1[20];
 
 static unsigned int sha1_file_open_flag = O_NOATIME;
 
-signed char hexval_table[256] = {
+const signed char hexval_table[256] = {
 	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 00-07 */
 	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 08-0f */
 	 -1, -1, -1, -1, -1, -1, -1, -1,		/* 10-17 */

Original file line number	Diff line number	Diff line change
`@@ -302,8 +302,8 @@ extern int legacy_loose_object(unsigned char *);`
`302`	`302`	`extern int has_pack_file(const unsigned char *sha1);`
`303`	`303`	`extern int has_pack_index(const unsigned char *sha1);`
`304`	`304`
`305`		`-extern signed char hexval_table[256];`
`306`		`-static inline unsigned int hexval(unsigned int c)`
	`305`	`+extern const signed char hexval_table[256];`
	`306`	`+static inline unsigned int hexval(unsigned char c)`
`307`	`307`	`{`
`308`	`308`	`return hexval_table[c];`
`309`	`309`	`}`