Re: [PATCH] hex <-> int conve

Re: [PATCH] hex <-> int conve

[Jakob Kemi]

On Tuesday 19 February 2002 19.02, Linus Torvalds wrote:
> On Tue, 19 Feb 2002, Jakob Kemi wrote:
> > I also added three other hex-functions that can replace a lot of
> > duplicated code.
> >
> > int  hexint_nibble (char x);		// hex digit to int.
> > int  hexint_byte   (const char *src);	// hex digit-pair to int.
> > char inthex_nibble (int x);		// int to hex digit.
> > void inthex_byte   (int x, char* dest);	// int to hex digit pair.
>
> Is there any reason to do all of this?
>
> I suspect 99% of all users can (and probably should) be replaced with
> "sscanf()" instead. Which does a lot more, of course, and is not the
> fastest thing out there due to that, but anybody who does hex->int
> conversion inside some critical loop is just crazy.

We needed the code when parsing non-null terminated UUID strings in the LDM
partition database (Dynamic Disks). And sscanf wouldn't work for us. Consider:

char a[3] = {'a','b'};
char b[3] = {'a','-'};
int x;
sscanf(a, "%x", &x);  // undefined, could crash since a isn't null-terminated

is probably solved by specifying width, but then consider:

sscanf(b, "%2x", &x); // would happily return 1 and fill x with 10

hexint_byte() would detect the error however.

Due to the amount of UUID's we have to parse the speed difference when using
sscanf() would also be noticeable. I suspect others have different reasons for
implementing their own hex->int functions.

Regards,
	Jakob Kemi

(Included is a smaller patch with less inlining.)


diff -urN -X dontdiff linux-2.5.5-pre1-vanilla/include/linux/hexint.h linux-2.5.5-pre1/include/linux/hexint.h
--- linux-2.5.5-pre1-vanilla/include/linux/hexint.h	Thu Jan  1 01:00:00 1970
+++ linux-2.5.5-pre1/include/linux/hexint.h	Tue Feb 19 19:14:35 2002
@@ -0,0 +1,66 @@
+/*
+ *  include/linux/hexint.h - hex<->int conversions.
+ *
+ *  Copyleft (C) 2002, Jakob Kemi <jakob.kemi@telia.com>
+ */
+
+#ifndef _LINUX_HEXINT_H
+#define _LINUX_HEXINT_H
+
+#ifdef __KERNEL__
+
+/**
+ * hexint_nibble - Convert a hex digit to an int.
+ * @x: digit to convert.
+ *
+ * Return:
+ *     converted value (0-15) on success.
+ *     -1 on failure.
+ */
+extern int hexint_nibble(char x);
+
+/**
+ * __hexint_nibble - Inlined version of hexint_nibble without error-checking.
+ */
+static __inline__ int __hexint_nibble(char x)
+{
+	const unsigned int y = x - '0';
+
+	if (y <= 9) return y;
+	return (y - 7) & 0x5f;
+}
+
+/**
+ * hexint_byte - Convert a hex digit pair to an int.
+ * @src: Pointer to source data.
+ *
+ * Return:
+ *     converted value (0-255) on success.
+ *     -1 on failure.
+ */
+extern int hexint_byte(const char *src);
+
+/**
+ * inthex_nibble - Convert an int to a hex digit.
+ */
+static __inline__ char inthex_nibble(int x)
+{
+	const char* digits = "0123456789abcdef";
+
+	return digits[x & 0x0f];
+}
+
+/**
+ * inthex_byte - Convert an int to a hex digit pair.
+ */
+static __inline__ void inthex_byte(int x, char* dest)
+{
+	const char* digits = "0123456789abcdef";
+
+	dest[0] = digits[(x & 0xf0) >> 4];
+	dest[1] = digits[x & 0x0f];
+}
+
+#endif /* __KERNEL__ */
+
+#endif
diff -urN -X dontdiff linux-2.5.5-pre1-vanilla/lib/Makefile linux-2.5.5-pre1/lib/Makefile
--- linux-2.5.5-pre1-vanilla/lib/Makefile	Sun Feb  3 14:04:47 2002
+++ linux-2.5.5-pre1/lib/Makefile	Tue Feb 19 15:55:37 2002
@@ -10,7 +10,7 @@
 
 export-objs := cmdline.o dec_and_lock.o rwsem-spinlock.o rwsem.o crc32.o
 
-obj-y := errno.o ctype.o string.o vsprintf.o brlock.o cmdline.o bust_spinlocks.o rbtree.o
+obj-y := errno.o ctype.o string.o vsprintf.o brlock.o cmdline.o bust_spinlocks.o rbtree.o hexint.o
 
 obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o
 obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
diff -urN -X dontdiff linux-2.5.5-pre1-vanilla/lib/hexint.c linux-2.5.5-pre1/lib/hexint.c
--- linux-2.5.5-pre1-vanilla/lib/hexint.c	Thu Jan  1 01:00:00 1970
+++ linux-2.5.5-pre1/lib/hexint.c	Tue Feb 19 19:12:37 2002
@@ -0,0 +1,50 @@
+/*
+ *  linux/lib/hexint.c - hex<->int conversions.
+ *
+ *  Copyleft (C) 2002, Jakob Kemi <jakob.kemi@telia.com>
+ */
+
+/**
+ * hexint_nibble - Convert a hex digit to an int.
+ * @x: digit to convert.
+ *
+ * Return:
+ *     converted value (0-15) on success.
+ *     -1 on failure.
+ */
+int hexint_nibble(char x)
+{
+	unsigned int y;		/* unsigned for correct wrapping */
+
+	if ((y = x - '0') <= '9'-'0') return y;
+	if ((y = x - 'a') <= 'f'-'a') return y+10;
+	if ((y = x - 'A') <= 'F'-'A') return y+10;
+	return -1;
+}
+
+/**
+ * hexint_byte - Convert an hex digit pair to an int.
+ * @src: Pointer to source data.
+ *
+ * Return:
+ *     converted value (0-255) on success.
+ *     -1 on failure.
+ */
+int hexint_byte(const char *src)
+{
+	unsigned int y; /* unsigned for correct wrapping. */
+	int h;
+
+	/* high part. */
+	if      ((y = src[0] - '0') <= '9'-'0') h = y;
+	else if ((y = src[0] - 'a') <= 'f'-'a') h = y+10;
+	else if ((y = src[0] - 'A') <= 'F'-'A') h = y+10;
+	else return -1;
+	h <<= 4;
+
+	/* low part. */
+	if ((y = src[1] - '0') <= '9'-'0') return h | y;
+	if ((y = src[1] - 'a') <= 'f'-'a') return h | (y+10);
+	if ((y = src[1] - 'A') <= 'F'-'A') return h | (y+10);
+	return -1;
+}

Re: [PATCH] hex <-> int conve

[Andreas Dilger]

On Feb 19, 2002  19:47 +0100, Jakob Kemi wrote:
> We needed the code when parsing non-null terminated UUID strings in the LDM
> partition database (Dynamic Disks). And sscanf wouldn't work for us. Consider:
> 
> char a[3] = {'a','b'};
> char b[3] = {'a','-'};
> int x;
> sscanf(a, "%x", &x);  // undefined, could crash since a isn't null-terminated

If it is a matter of UUID parsing, just add (or use existing) function
uuid_parse() similar to that in libuuid.  Some UUID-related functions were
added to the kernel for ia64 GPM partitions, so this would just make the
UUID support in the kernel more complete.

Note that unless LDM has some serious brain-damage, there should not be any
need to have these special functions, as the user-space UUID-related code
works just fine without them.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/

Re: [PATCH] hex <-> int conve

[Jakob Kemi]

On Tuesday 19 February 2002 20.56, Andreas Dilger wrote:
> If it is a matter of UUID parsing, just add (or use existing) function
> uuid_parse() similar to that in libuuid.  Some UUID-related functions were
> added to the kernel for ia64 GPM partitions, so this would just make the
> UUID support in the kernel more complete.

Yes it might be appropriate to use and/or extend those functions.


> Note that unless LDM has some serious brain-damage, there should not be any
> need to have these special functions, as the user-space UUID-related code
> works just fine without them.

Unfortunately LDM has some serious brain-damage, nothing we can't handle
though. We don't need these special functions, we can continue to have them
in ldm.c (I'm talking about the new cvs version, soon to hit 2.5). However,
for those who read the beginning of this thread, I also gave the reason for
adding them where others can use them. As I grepped through the kernel I
found 27 (!) different _implementations_ (I might have missed some with non-
obvious names) of hex to int functions all of them were using variations of a
form which compiles to (on x86) twice the size and double execution time of
this one. Not that speed really matters in this context. I also found a dozen
or so of different int to hex implementations. In order to reduce code
duplication and increase the homogeneity of the kernel I think it's a good
idea to use _one_ implementation.

Cheers,
	Jakob Kemi

Re: [PATCH] hex <-> int conve

[Alexander Viro]

On Wed, 20 Feb 2002, Jakob Kemi wrote:

> this one. Not that speed really matters in this context. I also found a dozen
> or so of different int to hex implementations. In order to reduce code
> duplication and increase the homogeneity of the kernel I think it's a good
> idea to use _one_ implementation.

In that case it will have to be sprintf/sscanf/strtoul, since this stuff is
not going away...