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Subject[PATCH] Allow PRNG to Use Faster SHA Code
This patch is a diff against 2.4.18-pre8. It allows the PRNG
(Pseudorandom Number Generator) in the kernel to take advantage of
faster (but slightly larger) SHA code that was already present in the
kernel.

Ben Pharr
ben@benpharr.com

diff -urN -X dontdiff linux-2.4.18-pre8plain/CREDITS linux-2.4.18-pre8/CREDITS
--- linux-2.4.18-pre8plain/CREDITS Tue Feb 5 00:50:33 2002
+++ linux-2.4.18-pre8/CREDITS Mon Feb 4 23:28:30 2002
@@ -2343,6 +2343,14 @@
S: 13353 Berlin
S: Germany

+N: Benjamin Pharr
+E: ben@benpharr.com
+W: http://www.benpharr.com
+P: 1024D/6859792C 7BF0 E432 3365 C1FC E0E3 0BE2 44E1 3E1E 6859 792C
+D: Pseudorandom Number Generator Configuration Options
+S: E-mail for current address
+S: Mississippi, USA
+
N: Emanuel Pirker
E: epirker@edu.uni-klu.ac.at
D: AIC5800 IEEE 1394, RAW I/O on 1394
diff -urN -X dontdiff linux-2.4.18-pre8plain/Documentation/Configure.help linux-2.4.18-pre8/Documentation/Configure.help
--- linux-2.4.18-pre8plain/Documentation/Configure.help Tue Feb 5 00:50:33 2002
+++ linux-2.4.18-pre8/Documentation/Configure.help Tue Feb 5 00:31:19 2002
@@ -17172,7 +17172,7 @@
will issue the hlt instruction if nothing is to be done, thereby
sending the processor to sleep and saving power.

-ACPI support
+acpi support
CONFIG_ACPI
ACPI/OSPM support for Linux is currently under development. As such,
this support is preliminary and EXPERIMENTAL. Configuring ACPI
@@ -24359,6 +24359,21 @@
order to effectively use VLANs. See the VLAN web page for more
information: http://www.candelatech.com/~greear/vlan.html If unsure,
you can safely say 'N'.
+
+Smallest/Worst Performance SHA Code
+CONFIG_SHA_CODE_SIZE_0
+ Setting this will make the Pseudorandom Number Generator use the
+ smallest version of the SHA code, but also the slowest. It is 50%
+ slower than the largest/fastest version, but 6k smaller. This is
+ probably best for machines with small amounts of memory.
+
+Largest/Best Performance SHA Code
+CONFIG_SHA_CODE_SIZE_3
+ Setting this will make the Pseudorandom Number Generator use the
+ largest version of the SHA code, but also the fastest. It is
+ approximately twice as fast compared to the smallest/slowest code,
+ but 6kB larger. This is the obvious default for machines with
+ adequate amounts of memory.

#
# A couple of things I keep forgetting:
diff -urN -X dontdiff linux-2.4.18-pre8plain/drivers/char/Config.in linux-2.4.18-pre8/drivers/char/Config.in
--- linux-2.4.18-pre8plain/drivers/char/Config.in Tue Feb 5 00:50:35 2002
+++ linux-2.4.18-pre8/drivers/char/Config.in Tue Feb 5 00:21:41 2002
@@ -105,6 +105,11 @@
dep_tristate 'Support for user-space parallel port device drivers' CONFIG_PPDEV $CONFIG_PARPORT
fi

+comment 'Pseudorandom Number Generator Options'
+choice 'SHA Code Size/Performance' \
+ "Smallest/Slowest CONFIG_SHA_CODE_SIZE_0 \
+ Largest/Fastest CONFIG_SHA_CODE_SIZE_3" Largest/Fastest
+
source drivers/i2c/Config.in

mainmenu_option next_comment
diff -urN -X dontdiff linux-2.4.18-pre8plain/drivers/char/random.c linux-2.4.18-pre8/drivers/char/random.c
--- linux-2.4.18-pre8plain/drivers/char/random.c Fri Nov 9 16:01:21 2001
+++ linux-2.4.18-pre8/drivers/char/random.c Tue Feb 5 00:19:36 2002
@@ -863,8 +863,14 @@
#define HASH_EXTRA_SIZE 80
#define HASH_TRANSFORM SHATransform

-/* Various size/speed tradeoffs are available. Choose 0..3. */
-#define SHA_CODE_SIZE 0
+/* Various size/speed tradeoffs are available. Defined in
+ * kernel configuration files.
+ *
+ * CONFIG_SHA_CODE_SIZE_0 smallest/slowest
+ * CONFIG_SHA_CODE_SIZE_1
+ * CONFIG_SHA_CODE_SIZE_2
+ * CONFIG_SHA_CODE_SIZE_3 largest/fastest
+ */

/*
* SHA transform algorithm, taken from code written by Peter Gutmann,
@@ -918,7 +924,7 @@
E = digest[ 4 ];

/* Heavy mangling, in 4 sub-rounds of 20 iterations each. */
-#if SHA_CODE_SIZE == 0
+#ifdef CONFIG_SHA_CODE_SIZE_0
/*
* Approximately 50% of the speed of the largest version, but
* takes up 1/16 the space. Saves about 6k on an i386 kernel.
@@ -938,7 +944,8 @@
TEMP += ROTL(5, A) + E + W[i];
E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
}
-#elif SHA_CODE_SIZE == 1
+#endif
+#ifdef CONFIG_SHA_CODE_SIZE_1
for (i = 0; i < 20; i++) {
TEMP = f1(B, C, D) + K1 + ROTL(5, A) + E + W[i];
E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
@@ -955,7 +962,8 @@
TEMP = f4(B, C, D) + K4 + ROTL(5, A) + E + W[i];
E = D; D = C; C = ROTL(30, B); B = A; A = TEMP;
}
-#elif SHA_CODE_SIZE == 2
+#endif
+#ifdef CONFIG_SHA_CODE_SIZE_2
for (i = 0; i < 20; i += 5) {
subRound( A, B, C, D, E, f1, K1, W[ i ] );
subRound( E, A, B, C, D, f1, K1, W[ i+1 ] );
@@ -984,7 +992,8 @@
subRound( C, D, E, A, B, f4, K4, W[ i+3 ] );
subRound( B, C, D, E, A, f4, K4, W[ i+4 ] );
}
-#elif SHA_CODE_SIZE == 3 /* Really large version */
+#endif
+#ifdef CONFIG_SHA_CODE_SIZE_3 /* Really large version */
subRound( A, B, C, D, E, f1, K1, W[ 0 ] );
subRound( E, A, B, C, D, f1, K1, W[ 1 ] );
subRound( D, E, A, B, C, f1, K1, W[ 2 ] );
@@ -1068,8 +1077,6 @@
subRound( D, E, A, B, C, f4, K4, W[ 77 ] );
subRound( C, D, E, A, B, f4, K4, W[ 78 ] );
subRound( B, C, D, E, A, f4, K4, W[ 79 ] );
-#else
-#error Illegal SHA_CODE_SIZE
#endif

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