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Message-ID: <20140923102742.13288.qmail@ns.horizon.com>
Date: 23 Sep 2014 06:27:42 -0400
From: "George Spelvin" <linux@...izon.com>
To: linux-ext4@...r.kernel.org
Cc: linux@...izon.com, tytso@....edu
Subject: [PATCH v1 8/10] dirhash.c: Add siphash24()
Not hooked up to anything yet.
Signed-off-by: George Spelvin <linux@...izon.com>
---
Is there a nicer way to implement get_unaligned_le64()?
I know we all hate #ifdef, but I was tempted by the Dark Side.
lib/ext2fs/dirhash.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 126 insertions(+)
diff --git a/lib/ext2fs/dirhash.c b/lib/ext2fs/dirhash.c
index 048486e..f51a342 100644
--- a/lib/ext2fs/dirhash.c
+++ b/lib/ext2fs/dirhash.c
@@ -14,6 +14,7 @@
#include "config.h"
#include <stdio.h>
#include <string.h>
+#include <stdint.h>
#include "ext2_fs.h"
#include "ext2fs.h"
@@ -174,6 +175,131 @@ static void str2hashbuf(const char *msg, int len, __u32 *buf, int num,
*buf++ = pad;
}
+#if __i386 || __x86_64
+/* This is such a common case it's worth optimizing */
+# define get_unaligned_le64(p) (*(const __u64 *)(p))
+#else
+#if __GNUC__ >= 3
+__attribute__ ((__pure__))
+#endif
+static __u64 get_unaligned_le64(const void *p)
+{
+ const __u8 *q = p;
+
+ return (__u64)q[0] |
+ (__u64)q[1] << 8 |
+ (__u64)q[2] << 16 |
+ (__u64)q[3] << 24 |
+ (__u64)q[4] << 32 |
+ (__u64)q[5] << 40 |
+ (__u64)q[6] << 48 |
+ (__u64)q[7] << 56;
+}
+#endif
+
+#define rol64(x, s) ((x) << (s) | (x) >> (64 - (s)))
+
+/* The basic ARX mixing function, taken from Skein */
+#define SIP_MIX(a, b, s) ((a) += (b), (b) = rol64(b, s), (b) ^= (a))
+
+/*
+ * The complete SipRound. Note that, when unrolled twice like below,
+ * the 32-bit rotates drop out on 32-bit machines.
+ */
+#define SIP_ROUND(a, b, c, d) \
+ (SIP_MIX(a, b, 13), SIP_MIX(c, d, 16), (a) = rol64(a, 32), \
+ SIP_MIX(c, b, 17), SIP_MIX(a, d, 21), (c) = rol64(c, 32))
+
+#if __GNUC__ >= 3
+__attribute__ ((__pure__))
+#endif
+static __u64
+siphash24(char const *in, size_t len, __u32 const seed[4])
+{
+ __u64 a = 0x736f6d6570736575ull; /* somepseu */
+ __u64 b = 0x646f72616e646f6dull; /* dorandom */
+ __u64 c = 0x6c7967656e657261ull; /* lygenera */
+ __u64 d = 0x7465646279746573ull; /* tedbytes */
+ __u64 m = 0;
+ __u8 padbyte = len;
+
+ /*
+ * Mix in the 128-bit hash seed. This is in a format convenient
+ * to the ext3/ext4 code. Please feel free to adapt the
+ * */
+ if (seed) {
+ m = seed[2] | (__u64)seed[3] << 32;
+ b ^= m;
+ d ^= m;
+ m = seed[0] | (__u64)seed[1] << 32;
+ /* a ^= m; is done in loop below */
+ c ^= m;
+ }
+
+ /*
+ * By using the same SipRound code for all iterations, we
+ * save space, at the expense of some branch prediction. But
+ * branch prediction is hard because of variable length anyway.
+ */
+ len = len/8 + 3; /* Now number of rounds to perform */
+ do {
+ a ^= m;
+
+ switch (--len) {
+ unsigned bytes;
+
+ default: /* Full words */
+ d ^= m = get_unaligned_le64(in);
+ in += 8;
+ break;
+ case 2: /* Final partial word */
+ /*
+ * We'd like to do one 64-bit fetch rather than
+ * mess around with bytes, but reading past the end
+ * might hit a protection boundary. Fortunately,
+ * we know that protection boundaries are aligned,
+ * so we can consider only three cases:
+ * - The remainder occupies zero words
+ * - The remainder fits into one word
+ * - The remainder straddles two words
+ */
+ bytes = padbyte & 7;
+
+ if (bytes == 0) {
+ m = 0;
+ } else {
+ unsigned offset = (unsigned)(uintptr_t)in & 7;
+
+ if (offset + bytes <= 8) {
+ m = ext2fs_le64_to_cpu(*(__u64 const *)
+ (in - offset));
+ m >>= 8*offset;
+ } else {
+ m = get_unaligned_le64(in);
+ }
+ m &= ((__u64)1 << 8*bytes) - 1;
+ }
+ /* Could use | or +, but ^ allows associativity */
+ d ^= m ^= (__u64)padbyte << 56;
+ break;
+ case 1: /* Beginning of finalization */
+ m = 0;
+ c ^= 0xff;
+ /*FALLTHROUGH*/
+ case 0:
+ break;
+ }
+
+ SIP_ROUND(a, b, c, d);
+ SIP_ROUND(a, b, c, d);
+ } while (len);
+
+ return a ^ b ^ c ^ d;
+}
+
+#undef SIP_ROUND
+#undef SIP_MIX
+
/*
* Returns the hash of a filename. If len is 0 and name is NULL, then
* this function can be used to test whether or not a hash version is
--
2.1.0
--
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