--- /dev/null
+/*
+--------------------------------------------------------------------
+lookup2.c, by Bob Jenkins, December 1996, Public Domain.
+hash(), hash2(), hash3, and mix() 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 has no warranty.
+--------------------------------------------------------------------
+*/
+#include <stdio.h>
+#include <stddef.h>
+#include <stdlib.h>
+typedef unsigned long int ub4; /* unsigned 4-byte quantities */
+typedef unsigned char ub1;
+
+#define hashsize(n) ((ub4)1<<(n))
+#define hashmask(n) (hashsize(n)-1)
+
+/*
+--------------------------------------------------------------------
+mix -- mix 3 32-bit values reversibly.
+For every delta with one or two bit set, and the deltas of all three
+ high bits or all three low bits, whether the original value of a,b,c
+ is almost all zero or is uniformly distributed,
+* If mix() is run forward or backward, at least 32 bits in a,b,c
+ have at least 1/4 probability of changing.
+* If mix() is run forward, every bit of c will change between 1/3 and
+ 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
+mix() was built out of 36 single-cycle latency instructions in a
+ structure that could supported 2x parallelism, like so:
+ a -= b;
+ a -= c; x = (c>>13);
+ b -= c; a ^= x;
+ b -= a; x = (a<<8);
+ c -= a; b ^= x;
+ c -= b; x = (b>>13);
+ ...
+ Unfortunately, superscalar Pentiums and Sparcs can't take advantage
+ of that parallelism. They've also turned some of those single-cycle
+ latency instructions into multi-cycle latency instructions. Still,
+ this is the fastest good hash I could find. There were about 2^^68
+ to choose from. I only looked at a billion or so.
+--------------------------------------------------------------------
+*/
+#define mix(a,b,c) \
+{ \
+ a -= b; a -= c; a ^= (c>>13); \
+ b -= c; b -= a; b ^= (a<<8); \
+ c -= a; c -= b; c ^= (b>>13); \
+ a -= b; a -= c; a ^= (c>>12); \
+ b -= c; b -= a; b ^= (a<<16); \
+ c -= a; c -= b; c ^= (b>>5); \
+ a -= b; a -= c; a ^= (c>>3); \
+ b -= c; b -= a; b ^= (a<<10); \
+ c -= a; c -= b; c ^= (b>>15); \
+}
+
+/* same, but slower, works on systems that might have 8 byte ub4's */
+#define mix2(a,b,c) \
+{ \
+ a -= b; a -= c; a ^= (c>>13); \
+ b -= c; b -= a; b ^= (a<< 8); \
+ c -= a; c -= b; c ^= ((b&0xffffffff)>>13); \
+ a -= b; a -= c; a ^= ((c&0xffffffff)>>12); \
+ b -= c; b -= a; b = (b ^ (a<<16)) & 0xffffffff; \
+ c -= a; c -= b; c = (c ^ (b>> 5)) & 0xffffffff; \
+ a -= b; a -= c; a = (a ^ (c>> 3)) & 0xffffffff; \
+ b -= c; b -= a; b = (b ^ (a<<10)) & 0xffffffff; \
+ c -= a; c -= b; c = (c ^ (b>>15)) & 0xffffffff; \
+}
+
+/*
+--------------------------------------------------------------------
+hash() -- hash a variable-length key into a 32-bit value
+ k : the key (the unaligned variable-length array of bytes)
+ len : the length of the key, counting by bytes
+ level : can be any 4-byte value
+Returns a 32-bit value. Every bit of the key affects every bit of
+the return value. Every 1-bit and 2-bit delta achieves avalanche.
+About 36+6len instructions.
+
+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 (ub1 **)k, do it like this:
+ for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
+
+By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this
+code any way you wish, private, educational, or commercial. It's free.
+
+See http://burlteburtle.net/bob/hash/evahash.html
+Use for hash table lookup, or anything where one collision in 2^32 is
+acceptable. Do NOT use for cryptographic purposes.
+--------------------------------------------------------------------
+*/
+
+ub4 hash( k, length, initval)
+register ub1 *k; /* the key */
+register ub4 length; /* the length of the key */
+register ub4 initval; /* the previous hash, or an arbitrary value */
+{
+ register ub4 a,b,c,len;
+
+ /* Set up the internal state */
+ len = length;
+ a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
+ c = initval; /* the previous hash value */
+
+ /*---------------------------------------- handle most of the key */
+ while (len >= 12)
+ {
+ a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
+ b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
+ c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
+ mix(a,b,c);
+ k += 12; len -= 12;
+ }
+
+ /*------------------------------------- handle the last 11 bytes */
+ c += length;
+ switch(len) /* all the case statements fall through */
+ {
+ case 11: c+=((ub4)k[10]<<24);
+ case 10: c+=((ub4)k[9]<<16);
+ case 9 : c+=((ub4)k[8]<<8);
+ /* the first byte of c is reserved for the length */
+ case 8 : b+=((ub4)k[7]<<24);
+ case 7 : b+=((ub4)k[6]<<16);
+ case 6 : b+=((ub4)k[5]<<8);
+ case 5 : b+=k[4];
+ case 4 : a+=((ub4)k[3]<<24);
+ case 3 : a+=((ub4)k[2]<<16);
+ case 2 : a+=((ub4)k[1]<<8);
+ case 1 : a+=k[0];
+ /* case 0: nothing left to add */
+ }
+ mix(a,b,c);
+ /*-------------------------------------------- report the result */
+ return c;
+}
+
+
+/*
+--------------------------------------------------------------------
+ This works on all machines. hash2() is identical to hash() on
+ little-endian machines, except that the length has to be measured
+ in ub4s instead of bytes. It is much faster than hash(). It
+ requires
+ -- that the key be an array of ub4's, and
+ -- that all your machines have the same endianness, and
+ -- that the length be the number of ub4's in the key
+--------------------------------------------------------------------
+*/
+ub4 hash2( k, length, initval)
+register ub4 *k; /* the key */
+register ub4 length; /* the length of the key, in ub4s */
+register ub4 initval; /* the previous hash, or an arbitrary value */
+{
+ register ub4 a,b,c,len;
+
+ /* Set up the internal state */
+ len = length;
+ a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
+ c = initval; /* the previous hash value */
+
+ /*---------------------------------------- handle most of the key */
+ while (len >= 3)
+ {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ mix(a,b,c);
+ k += 3; len -= 3;
+ }
+
+ /*-------------------------------------- handle the last 2 ub4's */
+ c += length;
+ switch(len) /* all the case statements fall through */
+ {
+ /* c is reserved for the length */
+ case 2 : b+=k[1];
+ case 1 : a+=k[0];
+ /* case 0: nothing left to add */
+ }
+ mix(a,b,c);
+ /*-------------------------------------------- report the result */
+ return c;
+}
+
+/*
+--------------------------------------------------------------------
+ This is identical to hash() on little-endian machines (like Intel
+ x86s or VAXen). It gives nondeterministic results on big-endian
+ machines. It is faster than hash(), but a little slower than
+ hash2(), and it requires
+ -- that all your machines be little-endian
+--------------------------------------------------------------------
+*/
+
+ub4 hash3( k, length, initval)
+register ub1 *k; /* the key */
+register ub4 length; /* the length of the key */
+register ub4 initval; /* the previous hash, or an arbitrary value */
+{
+ register ub4 a,b,c,len;
+
+ /* Set up the internal state */
+ len = length;
+ a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
+ c = initval; /* the previous hash value */
+
+ /*---------------------------------------- handle most of the key */
+ if (((ub4)k)&3)
+ {
+ while (len >= 12) /* unaligned */
+ {
+ a += (k[0] +((ub4)k[1]<<8) +((ub4)k[2]<<16) +((ub4)k[3]<<24));
+ b += (k[4] +((ub4)k[5]<<8) +((ub4)k[6]<<16) +((ub4)k[7]<<24));
+ c += (k[8] +((ub4)k[9]<<8) +((ub4)k[10]<<16)+((ub4)k[11]<<24));
+ mix(a,b,c);
+ k += 12; len -= 12;
+ }
+ }
+ else
+ {
+ while (len >= 12) /* aligned */
+ {
+ a += *(ub4 *)(k+0);
+ b += *(ub4 *)(k+4);
+ c += *(ub4 *)(k+8);
+ mix(a,b,c);
+ k += 12; len -= 12;
+ }
+ }
+
+ /*------------------------------------- handle the last 11 bytes */
+ c += length;
+ switch(len) /* all the case statements fall through */
+ {
+ case 11: c+=((ub4)k[10]<<24);
+ case 10: c+=((ub4)k[9]<<16);
+ case 9 : c+=((ub4)k[8]<<8);
+ /* the first byte of c is reserved for the length */
+ case 8 : b+=((ub4)k[7]<<24);
+ case 7 : b+=((ub4)k[6]<<16);
+ case 6 : b+=((ub4)k[5]<<8);
+ case 5 : b+=k[4];
+ case 4 : a+=((ub4)k[3]<<24);
+ case 3 : a+=((ub4)k[2]<<16);
+ case 2 : a+=((ub4)k[1]<<8);
+ case 1 : a+=k[0];
+ /* case 0: nothing left to add */
+ }
+ mix(a,b,c);
+ /*-------------------------------------------- report the result */
+ return c;
+}
+
+
+
+#ifdef SELF_TEST
+
+/* used for timings */
+void driver1()
+{
+ ub4 buf[256];
+ ub4 i;
+ ub4 h=0;
+
+ for (i=0; i<256; ++i)
+ {
+ h = hash(buf,i,h);
+ }
+}
+
+/* check that every input bit changes every output bit half the time */
+#define HASHSTATE 1
+#define HASHLEN 1
+#define MAXPAIR 80
+#define MAXLEN 70
+void driver2()
+{
+ ub1 qa[MAXLEN+1], qb[MAXLEN+2], *a = &qa[0], *b = &qb[1];
+ ub4 c[HASHSTATE], d[HASHSTATE], i, j=0, k, l, m, z;
+ ub4 e[HASHSTATE],f[HASHSTATE],g[HASHSTATE],h[HASHSTATE];
+ ub4 x[HASHSTATE],y[HASHSTATE];
+ ub4 hlen;
+
+ printf("No more than %d trials should ever be needed \n",MAXPAIR/2);
+ for (hlen=0; hlen < MAXLEN; ++hlen)
+ {
+ z=0;
+ for (i=0; i<hlen; ++i) /*----------------------- for each input byte, */
+ {
+ for (j=0; j<8; ++j) /*------------------------ for each input bit, */
+ {
+ for (m=1; m<8; ++m) /*------------ for serveral possible initvals, */
+ {
+ for (l=0; l<HASHSTATE; ++l) e[l]=f[l]=g[l]=h[l]=x[l]=y[l]=~((ub4)0);
+
+ /*---- check that every output bit is affected by that input bit */
+ for (k=0; k<MAXPAIR; k+=2)
+ {
+ ub4 finished=1;
+ /* keys have one bit different */
+ for (l=0; l<hlen+1; ++l) {a[l] = b[l] = (ub1)0;}
+ /* have a and b be two keys differing in only one bit */
+ a[i] ^= (k<<j);
+ a[i] ^= (k>>(8-j));
+ c[0] = hash(a, hlen, m);
+ b[i] ^= ((k+1)<<j);
+ b[i] ^= ((k+1)>>(8-j));
+ d[0] = hash(b, hlen, m);
+ /* check every bit is 1, 0, set, and not set at least once */
+ for (l=0; l<HASHSTATE; ++l)
+ {
+ e[l] &= (c[l]^d[l]);
+ f[l] &= ~(c[l]^d[l]);
+ g[l] &= c[l];
+ h[l] &= ~c[l];
+ x[l] &= d[l];
+ y[l] &= ~d[l];
+ if (e[l]|f[l]|g[l]|h[l]|x[l]|y[l]) finished=0;
+ }
+ if (finished) break;
+ }
+ if (k>z) z=k;
+ if (k==MAXPAIR)
+ {
+ printf("Some bit didn't change: ");
+ printf("%.8lx %.8lx %.8lx %.8lx %.8lx %.8lx ",
+ e[0],f[0],g[0],h[0],x[0],y[0]);
+ printf("i %ld j %ld m %ld len %ld\n",i,j,m,hlen);
+ }
+ if (z==MAXPAIR) goto done;
+ }
+ }
+ }
+ done:
+ if (z < MAXPAIR)
+ {
+ printf("Mix success %2ld bytes %2ld initvals ",i,m);
+ printf("required %ld trials\n",z/2);
+ }
+ }
+ printf("\n");
+}
+
+/* Check for reading beyond the end of the buffer and alignment problems */
+void driver3()
+{
+ ub1 buf[MAXLEN+20], *b;
+ ub4 len;
+ ub1 q[] = "This is the time for all good men to come to the aid of their country";
+ ub1 qq[] = "xThis is the time for all good men to come to the aid of their country";
+ ub1 qqq[] = "xxThis is the time for all good men to come to the aid of their country";
+ ub1 qqqq[] = "xxxThis is the time for all good men to come to the aid of their country";
+ ub4 h,i,j,ref,x,y;
+
+ printf("Endianness. These should all be the same:\n");
+ printf("%.8lx\n", hash(q, sizeof(q)-1, (ub4)0));
+ printf("%.8lx\n", hash(qq+1, sizeof(q)-1, (ub4)0));
+ printf("%.8lx\n", hash(qqq+2, sizeof(q)-1, (ub4)0));
+ printf("%.8lx\n", hash(qqqq+3, sizeof(q)-1, (ub4)0));
+ printf("\n");
+ for (h=0, b=buf+1; h<8; ++h, ++b)
+ {
+ for (i=0; i<MAXLEN; ++i)
+ {
+ len = i;
+ for (j=0; j<i; ++j) *(b+j)=0;
+
+ /* these should all be equal */
+ ref = hash(b, len, (ub4)1);
+ *(b+i)=(ub1)~0;
+ *(b-1)=(ub1)~0;
+ x = hash(b, len, (ub4)1);
+ y = hash(b, len, (ub4)1);
+ if ((ref != x) || (ref != y))
+ {
+ printf("alignment error: %.8lx %.8lx %.8lx %ld %ld\n",ref,x,y,h,i);
+ }
+ }
+ }
+}
+
+/* check for problems with nulls */
+ void driver4()
+{
+ ub1 buf[1];
+ ub4 h,i,state[HASHSTATE];
+
+
+ buf[0] = ~0;
+ for (i=0; i<HASHSTATE; ++i) state[i] = 1;
+ printf("These should all be different\n");
+ for (i=0, h=0; i<8; ++i)
+ {
+ h = hash(buf, (ub4)0, h);
+ printf("%2ld 0-byte strings, hash is %.8lx\n", i, h);
+ }
+}
+
+
+int main()
+{
+ driver1(); /* test that the key is hashed: used for timings */
+ driver2(); /* test that whole key is hashed thoroughly */
+ driver3(); /* test that nothing but the key is hashed */
+ driver4(); /* test hashing multiple buffers (all buffers are null) */
+ return 1;
+}
+
+#endif /* SELF_TEST */
projects / ldid.git / commitdiff
