--- /dev/null
+/**
+ * Seccomp Library hash code
+ *
+ * Release under the Public Domain
+ * Author: Bob Jenkins <bob_jenkins@burtleburtle.net>
+ */
+
+/*
+ * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ *
+ * These are functions for producing 32-bit hashes for hash table lookup.
+ * jhash_word(), jhash_le(), jhash_be(), mix(), and final() are externally useful
+ * functions. Routines to test the hash are included if SELF_TEST is defined.
+ * You can use this free for any purpose. It's in the public domain. It has
+ * no warranty.
+ *
+ * You probably want to use jhash_le(). jhash_le() and jhash_be() hash byte
+ * arrays. jhash_le() is is faster than jhash_be() on little-endian machines.
+ * Intel and AMD are little-endian machines.
+ *
+ * If you want to find a hash of, say, exactly 7 integers, do
+ * a = i1; b = i2; c = i3;
+ * mix(a,b,c);
+ * a += i4; b += i5; c += i6;
+ * mix(a,b,c);
+ * a += i7;
+ * final(a,b,c);
+ *
+ * then use c as the hash value. If you have a variable length array of
+ * 4-byte integers to hash, use jhash_word(). If you have a byte array (like
+ * a character string), use jhash_le(). If you have several byte arrays, or
+ * a mix of things, see the comments above jhash_le().
+ *
+ * Why is this so big? I read 12 bytes at a time into 3 4-byte integers, then
+ * mix those integers. This is fast (you can do a lot more thorough mixing
+ * with 12*3 instructions on 3 integers than you can with 3 instructions on 1
+ * byte), but shoehorning those bytes into integers efficiently is messy.
+ */
+
+#include <stdint.h>
+
+#include "arch.h"
+#include "hash.h"
+
+#define hashsize(n) ((uint32_t)1<<(n))
+#define hashmask(n) (hashsize(n)-1)
+#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
+
+/**
+ * Mix 3 32-bit values reversibly
+ * @param a 32-bit value
+ * @param b 32-bit value
+ * @param c 32-bit value
+ *
+ * This is reversible, so any information in (a,b,c) before mix() is still
+ * in (a,b,c) after mix().
+ *
+ * If four pairs of (a,b,c) inputs are run through mix(), or through mix() in
+ * reverse, there are at least 32 bits of the output that are sometimes the
+ * same for one pair and different for another pair.
+ *
+ * This was tested for:
+ * - pairs that differed by one bit, by two bits, in any combination of top
+ * bits of (a,b,c), or in any combination of bottom bits of (a,b,c).
+ * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed the
+ * output delta to a Gray code (a^(a>>1)) so a string of 1's (as is commonly
+ * produced by subtraction) look like a single 1-bit difference.
+ * - the base values were pseudorandom, all zero but one bit set, or all zero
+ * plus a counter that starts at zero.
+ *
+ * Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
+ * satisfy this are
+ * 4 6 8 16 19 4
+ * 9 15 3 18 27 15
+ * 14 9 3 7 17 3
+ *
+ * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing for "differ"
+ * defined as + with a one-bit base and a two-bit delta. I used
+ * http://burtleburtle.net/bob/hash/avalanche.html to choose the operations,
+ * constants, and arrangements of the variables.
+ *
+ * This does not achieve avalanche. There are input bits of (a,b,c) that fail
+ * to affect some output bits of (a,b,c), especially of a. The most thoroughly
+ * mixed value is c, but it doesn't really even achieve avalanche in c.
+ *
+ * This allows some parallelism. Read-after-writes are good at doubling the
+ * number of bits affected, so the goal of mixing pulls in the opposite
+ * direction as the goal of parallelism. I did what I could. Rotates seem to
+ * cost as much as shifts on every machine I could lay my hands on, and rotates
+ * are much kinder to the top and bottom bits, so I used rotates.
+ *
+ */
+#define mix(a,b,c) \
+ { \
+ a -= c; a ^= rot(c, 4); c += b; \
+ b -= a; b ^= rot(a, 6); a += c; \
+ c -= b; c ^= rot(b, 8); b += a; \
+ a -= c; a ^= rot(c,16); c += b; \
+ b -= a; b ^= rot(a,19); a += c; \
+ c -= b; c ^= rot(b, 4); b += a; \
+ }
+
+/**
+ * Final mixing of 3 32-bit values (a,b,c) into c
+ * @param a 32-bit value
+ * @param b 32-bit value
+ * @param c 32-bit value
+ *
+ * Pairs of (a,b,c) values differing in only a few bits will usually produce
+ * values of c that look totally different. This was tested for:
+ * - pairs that differed by one bit, by two bits, in any combination of top
+ * bits of (a,b,c), or in any combination of bottom bits of (a,b,c).
+ * - "differ" is defined as +, -, ^, or ~^. For + and -, I transformed the
+ * output delta to a Gray code (a^(a>>1)) so a string of 1's (as is commonly
+ * produced by subtraction) look like a single 1-bit difference.
+ * - the base values were pseudorandom, all zero but one bit set, or all zero
+ * plus a counter that starts at zero.
+ *
+ * These constants passed:
+ * 14 11 25 16 4 14 24
+ * 12 14 25 16 4 14 24
+ * and these came close:
+ * 4 8 15 26 3 22 24
+ * 10 8 15 26 3 22 24
+ * 11 8 15 26 3 22 24
+ *
+ */
+#define final(a,b,c) \
+ { \
+ c ^= b; c -= rot(b,14); \
+ a ^= c; a -= rot(c,11); \
+ b ^= a; b -= rot(a,25); \
+ c ^= b; c -= rot(b,16); \
+ a ^= c; a -= rot(c,4); \
+ b ^= a; b -= rot(a,14); \
+ c ^= b; c -= rot(b,24); \
+ }
+
+/**
+ * Hash an array of 32-bit values
+ * @param k the key, an array of uint32_t values
+ * @param length the number of array elements
+ * @param initval the previous hash, or an arbitrary value
+ *
+ * This works on all machines. To be useful, it requires:
+ * - that the key be an array of uint32_t's, and
+ * - that the length be the number of uint32_t's in the key
+ *
+ * The function jhash_word() is identical to jhash_le() on little-endian
+ * machines, and identical to jhash_be() on big-endian machines, except that
+ * the length has to be measured in uint32_ts rather than in bytes. jhash_le()
+ * is more complicated than jhash_word() only because jhash_le() has to dance
+ * around fitting the key bytes into registers.
+ *
+ */
+static uint32_t jhash_word(const uint32_t *k, size_t length, uint32_t initval)
+{
+ uint32_t a, b, c;
+
+ /* set up the internal state */
+ a = b = c = 0xdeadbeef + (((uint32_t)length) << 2) + initval;
+
+ /* handle most of the key */
+ while (length > 3) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ mix(a, b, c);
+ length -= 3;
+ k += 3;
+ }
+
+ /* handle the last 3 uint32_t's */
+ switch(length) {
+ case 3 :
+ c += k[2];
+ case 2 :
+ b += k[1];
+ case 1 :
+ a += k[0];
+ final(a, b, c);
+ case 0:
+ /* nothing left to add */
+ break;
+ }
+
+ return c;
+}
+
+/**
+ * Hash a variable-length key into a 32-bit value
+ * @param key the key (the unaligned variable-length array of bytes)
+ * @param length the length of the key, counting by bytes
+ * @param initval can be any 4-byte value
+ *
+ * Returns a 32-bit value. Every bit of the key affects every bit of the
+ * return value. Two keys differing by one or two bits will have totally
+ * different hash values.
+ *
+ * The best hash table sizes are powers of 2. There is no need to do mod a
+ * prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask.
+ * For example, if you need only 10 bits, do:
+ * h = (h & hashmask(10));
+ * In which case, the hash table should have hashsize(10) elements.
+ *
+ * If you are hashing n strings (uint8_t **)k, do it like this:
+ * for (i=0, h=0; i<n; ++i) h = jhash_le( k[i], len[i], h);
+ *
+ */
+static uint32_t jhash_le(const void *key, size_t length, uint32_t initval)
+{
+ uint32_t a, b, c;
+ union {
+ const void *ptr;
+ size_t i;
+ } u; /* needed for Mac Powerbook G4 */
+
+ /* set up the internal state */
+ a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
+
+ u.ptr = key;
+ if ((arch_def_native->endian == ARCH_ENDIAN_LITTLE) &&
+ ((u.i & 0x3) == 0)) {
+ /* read 32-bit chunks */
+ const uint32_t *k = (const uint32_t *)key;
+
+ while (length > 12) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ mix(a, b, c);
+ length -= 12;
+ k += 3;
+ }
+
+ /* "k[2]&0xffffff" actually reads beyond the end of the string,
+ * but then masks off the part it's not allowed to read.
+ * Because the string is aligned, the masked-off tail is in the
+ * same word as the rest of the string. Every machine with
+ * memory protection I've seen does it on word boundaries, so
+ * is OK with this. But VALGRIND will still catch it and
+ * complain. The masking trick does make the hash noticably
+ * faster for short strings (like English words). */
+#ifndef VALGRIND
+
+ switch(length) {
+ case 12:
+ c += k[2];
+ b += k[1];
+ a += k[0];
+ break;
+ case 11:
+ c += k[2] & 0xffffff;
+ b += k[1];
+ a += k[0];
+ break;
+ case 10:
+ c += k[2] & 0xffff;
+ b += k[1];
+ a += k[0];
+ break;
+ case 9 :
+ c += k[2] & 0xff;
+ b += k[1];
+ a += k[0];
+ break;
+ case 8 :
+ b += k[1];
+ a += k[0];
+ break;
+ case 7 :
+ b += k[1] & 0xffffff;
+ a += k[0];
+ break;
+ case 6 :
+ b += k[1] & 0xffff;
+ a += k[0];
+ break;
+ case 5 :
+ b += k[1] & 0xff;
+ a += k[0];
+ break;
+ case 4 :
+ a += k[0];
+ break;
+ case 3 :
+ a += k[0] & 0xffffff;
+ break;
+ case 2 :
+ a += k[0] & 0xffff;
+ break;
+ case 1 :
+ a += k[0] & 0xff;
+ break;
+ case 0 :
+ /* zero length strings require no mixing */
+ return c;
+ }
+
+#else /* make valgrind happy */
+
+ k8 = (const uint8_t *)k;
+ switch(length) {
+ case 12:
+ c += k[2];
+ b += k[1];
+ a += k[0];
+ break;
+ case 11:
+ c += ((uint32_t)k8[10]) << 16;
+ case 10:
+ c += ((uint32_t)k8[9]) << 8;
+ case 9 :
+ c += k8[8];
+ case 8 :
+ b += k[1];
+ a += k[0];
+ break;
+ case 7 :
+ b += ((uint32_t)k8[6]) << 16;
+ case 6 :
+ b += ((uint32_t)k8[5]) << 8;
+ case 5 :
+ b += k8[4];
+ case 4 :
+ a += k[0];
+ break;
+ case 3 :
+ a += ((uint32_t)k8[2]) << 16;
+ case 2 :
+ a += ((uint32_t)k8[1]) << 8;
+ case 1 :
+ a += k8[0];
+ break;
+ case 0 :
+ return c;
+ }
+
+#endif /* !valgrind */
+
+ } else if ((arch_def_native->endian == ARCH_ENDIAN_LITTLE) &&
+ ((u.i & 0x1) == 0)) {
+ /* read 16-bit chunks */
+ const uint16_t *k = (const uint16_t *)key;
+ const uint8_t *k8;
+
+ while (length > 12) {
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ b += k[2] + (((uint32_t)k[3]) << 16);
+ c += k[4] + (((uint32_t)k[5]) << 16);
+ mix(a, b, c);
+ length -= 12;
+ k += 6;
+ }
+
+ k8 = (const uint8_t *)k;
+ switch(length) {
+ case 12:
+ c += k[4] + (((uint32_t)k[5]) << 16);
+ b += k[2] + (((uint32_t)k[3]) << 16);
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ break;
+ case 11:
+ c += ((uint32_t)k8[10]) << 16;
+ case 10:
+ c += k[4];
+ b += k[2] + (((uint32_t)k[3]) << 16);
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ break;
+ case 9 :
+ c += k8[8];
+ case 8 :
+ b += k[2] + (((uint32_t)k[3]) << 16);
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ break;
+ case 7 :
+ b += ((uint32_t)k8[6]) << 16;
+ case 6 :
+ b += k[2];
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ break;
+ case 5 :
+ b += k8[4];
+ case 4 :
+ a += k[0] + (((uint32_t)k[1]) << 16);
+ break;
+ case 3 :
+ a += ((uint32_t)k8[2]) << 16;
+ case 2 :
+ a += k[0];
+ break;
+ case 1 :
+ a += k8[0];
+ break;
+ case 0 :
+ /* zero length requires no mixing */
+ return c;
+ }
+
+ } else {
+ /* need to read the key one byte at a time */
+ const uint8_t *k = (const uint8_t *)key;
+
+ while (length > 12) {
+ a += k[0];
+ a += ((uint32_t)k[1]) << 8;
+ a += ((uint32_t)k[2]) << 16;
+ a += ((uint32_t)k[3]) << 24;
+ b += k[4];
+ b += ((uint32_t)k[5]) << 8;
+ b += ((uint32_t)k[6]) << 16;
+ b += ((uint32_t)k[7]) << 24;
+ c += k[8];
+ c += ((uint32_t)k[9]) << 8;
+ c += ((uint32_t)k[10]) << 16;
+ c += ((uint32_t)k[11]) << 24;
+ mix(a, b, c);
+ length -= 12;
+ k += 12;
+ }
+
+ switch(length) {
+ case 12:
+ c += ((uint32_t)k[11]) << 24;
+ case 11:
+ c += ((uint32_t)k[10]) << 16;
+ case 10:
+ c += ((uint32_t)k[9]) << 8;
+ case 9 :
+ c += k[8];
+ case 8 :
+ b += ((uint32_t)k[7]) << 24;
+ case 7 :
+ b += ((uint32_t)k[6]) << 16;
+ case 6 :
+ b += ((uint32_t)k[5]) << 8;
+ case 5 :
+ b += k[4];
+ case 4 :
+ a += ((uint32_t)k[3]) << 24;
+ case 3 :
+ a += ((uint32_t)k[2]) << 16;
+ case 2 :
+ a += ((uint32_t)k[1]) << 8;
+ case 1 :
+ a += k[0];
+ break;
+ case 0 :
+ return c;
+ }
+ }
+
+ final(a, b, c);
+ return c;
+}
+
+/**
+ * Hash a variable-length key into a 32-bit value
+ * @param key the key (the unaligned variable-length array of bytes)
+ * @param length the length of the key, counting by bytes
+ * @param initval can be any 4-byte value
+ *
+ * This is the same as jhash_word() on big-endian machines. It is different
+ * from jhash_le() on all machines. jhash_be() takes advantage of big-endian
+ * byte ordering.
+ *
+ */
+static uint32_t jhash_be( const void *key, size_t length, uint32_t initval)
+{
+ uint32_t a, b, c;
+ union {
+ const void *ptr;
+ size_t i;
+ } u; /* to cast key to (size_t) happily */
+
+ /* set up the internal state */
+ a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
+
+ u.ptr = key;
+ if ((arch_def_native->endian == ARCH_ENDIAN_BIG) &&
+ ((u.i & 0x3) == 0)) {
+ /* read 32-bit chunks */
+ const uint32_t *k = (const uint32_t *)key;
+
+ while (length > 12) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ mix(a, b, c);
+ length -= 12;
+ k += 3;
+ }
+
+ /* "k[2]<<8" actually reads beyond the end of the string, but
+ * then shifts out the part it's not allowed to read. Because
+ * the string is aligned, the illegal read is in the same word
+ * as the rest of the string. Every machine with memory
+ * protection I've seen does it on word boundaries, so is OK
+ * with this. But VALGRIND will still catch it and complain.
+ * The masking trick does make the hash noticably faster for
+ * short strings (like English words). */
+#ifndef VALGRIND
+
+ switch(length) {
+ case 12:
+ c += k[2];
+ b += k[1];
+ a += k[0];
+ break;
+ case 11:
+ c += k[2] & 0xffffff00;
+ b += k[1];
+ a += k[0];
+ break;
+ case 10:
+ c += k[2] & 0xffff0000;
+ b += k[1];
+ a += k[0];
+ break;
+ case 9 :
+ c += k[2] & 0xff000000;
+ b += k[1];
+ a += k[0];
+ break;
+ case 8 :
+ b += k[1];
+ a += k[0];
+ break;
+ case 7 :
+ b += k[1] & 0xffffff00;
+ a += k[0];
+ break;
+ case 6 :
+ b += k[1] & 0xffff0000;
+ a += k[0];
+ break;
+ case 5 :
+ b += k[1] & 0xff000000;
+ a += k[0];
+ break;
+ case 4 :
+ a += k[0];
+ break;
+ case 3 :
+ a += k[0] & 0xffffff00;
+ break;
+ case 2 :
+ a += k[0] & 0xffff0000;
+ break;
+ case 1 :
+ a += k[0] & 0xff000000;
+ break;
+ case 0 :
+ /* zero length strings require no mixing */
+ return c;
+ }
+
+#else /* make valgrind happy */
+
+ k8 = (const uint8_t *)k;
+ switch(length) {
+ case 12:
+ c += k[2];
+ b += k[1];
+ a += k[0];
+ break;
+ case 11:
+ c += ((uint32_t)k8[10]) << 8;
+ case 10:
+ c += ((uint32_t)k8[9]) << 16;
+ case 9 :
+ c += ((uint32_t)k8[8]) << 24;
+ case 8 :
+ b += k[1];
+ a += k[0];
+ break;
+ case 7 :
+ b += ((uint32_t)k8[6]) << 8;
+ case 6 :
+ b += ((uint32_t)k8[5]) << 16;
+ case 5 :
+ b += ((uint32_t)k8[4]) << 24;
+ case 4 :
+ a += k[0];
+ break;
+ case 3 :
+ a += ((uint32_t)k8[2]) << 8;
+ case 2 :
+ a += ((uint32_t)k8[1]) << 16;
+ case 1 :
+ a += ((uint32_t)k8[0]) << 24;
+ break;
+ case 0 :
+ return c;
+ }
+
+#endif /* !VALGRIND */
+
+ } else {
+ /* need to read the key one byte at a time */
+ const uint8_t *k = (const uint8_t *)key;
+
+ while (length > 12) {
+ a += ((uint32_t)k[0]) << 24;
+ a += ((uint32_t)k[1]) << 16;
+ a += ((uint32_t)k[2]) << 8;
+ a += ((uint32_t)k[3]);
+ b += ((uint32_t)k[4]) << 24;
+ b += ((uint32_t)k[5]) << 16;
+ b += ((uint32_t)k[6]) << 8;
+ b += ((uint32_t)k[7]);
+ c += ((uint32_t)k[8]) << 24;
+ c += ((uint32_t)k[9]) << 16;
+ c += ((uint32_t)k[10]) << 8;
+ c += ((uint32_t)k[11]);
+ mix(a, b, c);
+ length -= 12;
+ k += 12;
+ }
+
+ switch(length) {
+ case 12:
+ c += k[11];
+ case 11:
+ c += ((uint32_t)k[10]) << 8;
+ case 10:
+ c += ((uint32_t)k[9]) << 16;
+ case 9 :
+ c += ((uint32_t)k[8]) << 24;
+ case 8 :
+ b += k[7];
+ case 7 :
+ b += ((uint32_t)k[6]) << 8;
+ case 6 :
+ b += ((uint32_t)k[5]) << 16;
+ case 5 :
+ b += ((uint32_t)k[4]) << 24;
+ case 4 :
+ a += k[3];
+ case 3 :
+ a += ((uint32_t)k[2]) << 8;
+ case 2 :
+ a += ((uint32_t)k[1]) << 16;
+ case 1 :
+ a += ((uint32_t)k[0]) << 24;
+ break;
+ case 0 :
+ return c;
+ }
+ }
+
+ final(a, b, c);
+ return c;
+}
+
+/**
+ * Hash a variable-length key into a 32-bit value
+ * @param key the key (the unaligned variable-length array of bytes)
+ * @param length the length of the key, counting by bytes
+ * @param initval can be any 4-byte value
+ *
+ * A small wrapper function that selects the proper hash function based on the
+ * native machine's byte-ordering.
+ *
+ */
+uint32_t jhash(const void *key, size_t length, uint32_t initval)
+{
+ if (length % sizeof(uint32_t) == 0)
+ return jhash_word(key, (length / sizeof(uint32_t)), initval);
+ else if (arch_def_native->endian == ARCH_ENDIAN_BIG)
+ return jhash_be(key, length, initval);
+ else
+ return jhash_le(key, length, initval);
+}
projects / linux-seccomp.git / blobdiff