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

["George Spelvin" <linux@sciencehorizons.net>]

>From a0d084b1225f2efcf4b5c81871c9c446155b9b13 Mon Sep 17 00:00:00 2001
From: George Spelvin <linux@sciencehorizons.net>
Date: Tue, 31 May 2016 16:00:22 -0400
Subject: [PATCH] lib/uuid.c: eliminate uuid_[bl]e_index arrays

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

uuid_[bl]e_index were EXPORT_SYMBOLed for no obvious reason; there
are no users outside of lib/.  The replacement uuid_[bl]e_pos arrays
are not exported pending finding a need.

The arrays are combined in one contiguous uuid_byte_pos[2][16]
array as a micro-optimization for uuid_string().  Choosing between
the two can be done by adding 16 rather than loading a second
full-word address.

x86-64 code size reductions:
uuid_string: was 228 bytes, now 134
__uuid_to_bin: was 119 bytes, now 85

Initialized data is also reduced by 16 bytes.

Signed-off-by: George Spelvin <linux@horizon.com>
---
Here's a patch implementing the suggestion I made earlier.  This reduces
code size, data size, and run time for input and output of UUIDs.

This patch is on top of the upper/lower case hex optimization for
lib/vsprintf.c I sent earlier.  If you don't have it, just ignore the
merge conflicts in uuid_string() and take the "after" version.

 include/linux/uuid.h |  6 ++++--
 lib/uuid.c           | 24 ++++++++++--------------
 lib/vsprintf.c       | 32 +++++++++++++-------------------
 3 files changed, 27 insertions(+), 35 deletions(-)

diff --git a/include/linux/uuid.h b/include/linux/uuid.h
index 2d095fc6..882d9ada 100644
--- a/include/linux/uuid.h
+++ b/include/linux/uuid.h
@@ -41,8 +41,10 @@ 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_byte_pos[2][16];
+#define uuid_be_pos (uuid_byte_pos[0])
+#define uuid_le_pos (uuid_byte_pos[1])
 
 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..8a439caf 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -21,10 +21,10 @@
 #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);
+const u8 uuid_byte_pos[2][16] = {
+	{0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34},	/* uuid_be_pos */
+	{6,4,2,0,11,9,16,14,19,21,24,26,28,30,32,34}	/* uuid_le_pos */
+};
 
 /***************************************************************
  * Random UUID interface
@@ -97,32 +97,28 @@ 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])
+static int __uuid_to_bin(const char uuid[36], __u8 b[16], const u8 si[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++)
+		if (hex2bin(b + i, uuid + si[i], 1) < 0)
+			return -EINVAL;
 
 	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..44faddb1 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':
+		pos = uuid_le_pos;
+		break;
 	case 'L':
-		hex = hex_asc_upper;	/* fall-through */
-	case 'l':
-		index = uuid_le_index;
-		break;
+		pos = uuid_le_pos;	/* Fall-through */
 	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