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Diffstat (limited to 'lookup2.c')
| -rw-r--r-- | lookup2.c | 416 |
1 files changed, 0 insertions, 416 deletions
diff --git a/lookup2.c b/lookup2.c deleted file mode 100644 index cd87c4d..0000000 --- a/lookup2.c +++ /dev/null @@ -1,416 +0,0 @@ -/* --------------------------------------------------------------------- -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 */ |