[PATCH v2 2/2] lib/uuid.c: eliminate uuid_[bl]e_index arrays

[George Spelvin]

Both input and output code is simplified if we use a mapping from binary
UUID index to ASCII UUID position.  This lets us combine hyphen-skipping
and endian-swapping into one table.

This significantly simplifies __uuid_to_bin(), which was using *two*
lookup tables.

uuid_[bl]e_index were EXPORT_SYMBOLed for no obvious reason; all users are
compiled unconditionally into the kernel.  The replacement uuid_[bl]e_pos
arrays are not exported until a need appears.

Benefits:
* The source code is shorter and simpler,
* it executes faster,
* initialized data is 16 bytes smaller, and
* compiled code is smaller.

Since this is not hot code, the important benchmark is not run time
but code size:

	uuid_string()			__uuid_to_bin()
	Before  After   Delta   Percent	Before  After   Delta   Percent
x86-32	199	196	 -3	 -1.5%	122	 90	-32	-26.2%
x86-64	186	162	-24	-12.9%	127	 90	-37	-29.1%
arm	264	216	-48	-18.2%	116	 92	-24	-20.7%
thumb	160	136	-24	-15.0%	100	 50	-50	-50.0%
arm64	244	188	-56	-23.0%	148	116	-32	-21.6%

Signed-off-by: George Spelvin <linux@xxxxxxxxxxx>
---
 include/linux/uuid.h |  5 +++--
 lib/uuid.c           | 24 +++++++++---------------
 lib/vsprintf.c       | 26 ++++++++++----------------
 3 files changed, 22 insertions(+), 33 deletions(-)

diff --git a/include/linux/uuid.h b/include/linux/uuid.h
index 2d095fc6..238f16f7 100644
--- a/include/linux/uuid.h
+++ b/include/linux/uuid.h
@@ -41,8 +41,9 @@ extern void uuid_be_gen(uuid_be *u);
 
 bool __must_check uuid_is_valid(const char *uuid);
 
-extern const u8 uuid_le_index[16];
-extern const u8 uuid_be_index[16];
+/* For each binary byte, string offset in ASCII UUID where it appears */
+extern const u8 uuid_be_pos[16];
+extern const u8 uuid_le_pos[16];
 
 int uuid_le_to_bin(const char *uuid, uuid_le *u);
 int uuid_be_to_bin(const char *uuid, uuid_be *u);
diff --git a/lib/uuid.c b/lib/uuid.c
index e116ae5f..93945915 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -21,11 +21,6 @@
 #include <linux/uuid.h>
 #include <linux/random.h>
 
-const u8 uuid_le_index[16] = {3,2,1,0,5,4,7,6,8,9,10,11,12,13,14,15};
-EXPORT_SYMBOL(uuid_le_index);
-const u8 uuid_be_index[16] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
-EXPORT_SYMBOL(uuid_be_index);
-
 /***************************************************************
  * Random UUID interface
  *
@@ -97,32 +92,31 @@ bool uuid_is_valid(const char *uuid)
 }
 EXPORT_SYMBOL(uuid_is_valid);
 
-static int __uuid_to_bin(const char *uuid, __u8 b[16], const u8 ei[16])
+/* For each binary byte, string offset in ASCII UUID where it appears */
+const u8 uuid_be_pos[16] = {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34};
+const u8 uuid_le_pos[16] = {6,4,2,0,11,9,16,14,19,21,24,26,28,30,32,34};
+
+static int __uuid_to_bin(const char uuid[36], __u8 b[16], const u8 pos[16])
 {
-	static const u8 si[16] = {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34};
 	unsigned int i;
 
 	if (!uuid_is_valid(uuid))
 		return -EINVAL;
 
-	for (i = 0; i < 16; i++) {
-		int hi = hex_to_bin(uuid[si[i]] + 0);
-		int lo = hex_to_bin(uuid[si[i]] + 1);
-
-		b[ei[i]] = (hi << 4) | lo;
-	}
+	for (i = 0; i < 16; i++)
+		hex2bin(b + i, uuid + pos[i], 1);
 
 	return 0;
 }
 
 int uuid_le_to_bin(const char *uuid, uuid_le *u)
 {
-	return __uuid_to_bin(uuid, u->b, uuid_le_index);
+	return __uuid_to_bin(uuid, u->b, uuid_le_pos);
 }
 EXPORT_SYMBOL(uuid_le_to_bin);
 
 int uuid_be_to_bin(const char *uuid, uuid_be *u)
 {
-	return __uuid_to_bin(uuid, u->b, uuid_be_index);
+	return __uuid_to_bin(uuid, u->b, uuid_be_pos);
 }
 EXPORT_SYMBOL(uuid_be_to_bin);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4ee07e89..f02cfd9f 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1313,38 +1313,32 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
 		  struct printf_spec spec, const char *fmt)
 {
 	char uuid[UUID_STRING_LEN + 1];
-	char *p = uuid;
 	int i;
-	const u8 *index = uuid_be_index;
+	const u8 *pos = uuid_be_pos;
 	const char *hex = hex_asc;
 
 	switch (fmt[1]) {
 	case 'L':
 		hex = hex_asc_upper;	/* fall-through */
 	case 'l':
-		index = uuid_le_index;
+		pos = uuid_le_pos;
 		break;
 	case 'B':
 		hex = hex_asc_upper;
 		break;
 	}
 
+	/* Format each byte of the raw uuid into the buffer */
 	for (i = 0; i < 16; i++) {
-		u8 byte = addr[index[i]];
+		u8 byte = addr[i];
+		char *p = uuid + pos[i];
 
-		*p++ = hex[byte >> 4];
-		*p++ = hex[byte & 0x0f];
-		switch (i) {
-		case 3:
-		case 5:
-		case 7:
-		case 9:
-			*p++ = '-';
-			break;
-		}
+		p[0] = hex[byte >> 4];
+		p[1] = hex[byte & 0x0f];
 	}
-
-	*p = 0;
+	/* Insert the fixed punctuation */
+	uuid[23] = uuid[18] = uuid[13] = uuid[8] = '-';
+	uuid[UUID_STRING_LEN] = '\0';
 
 	return string(buf, end, uuid, spec);
 }
-- 
2.8.1