Thursday, April 23, 2009

efficient hashtable

i've never seen a hashtable implementation, but i don't see how it could be more efficient than what i've come up with. according to the chart at , the 'generalized' crc algorithm has by far the best uniformity, and is one of the faster ones on the list (depending on how long your keys are, i guess). most, almost all, of those functions like to have table sizes in powers of two. so here's the algorithm, in unoptimized quasi-psuedo-code:
def init(orig_size): # must be power of two!
table_size = orig_size
table = malloc(table_size*whatever)
current_hash_bitmask = table_size-1

def add_key(key, value):
if table_size < (num_keys+1)*2:
_add_key(table, hash_function(key), key, value)

def del_key(key):
if table_size/2 > num_keys:

def double_table():
table_size *= 2
current_hash_bitmask = table_size-1
new_table = malloc(table_size)
for 32_bit_hash, key, value in table:
_add_key(new_table, 32_bit_hash & current_hash_bitmask, key, value)
table = new_table

def halve_table():
table_size /= 2
current_hash_bitmask = table_size-1
new_table = malloc(table_size)
for 32_bit_hash, key, value in table:
_add_key(new_table, 32_bit_hash & current_hash_bitmask, key, value)
table = new_table

def _add_key(table, 32_bit_hash, key, value);
insert 32_bit_hash, key and value into the linked list at
table[32_bit_hash & current_hash_bitmask]

def del_key(key):
should be obvious

def get_key(key):
should be obvious


i started making a very efficient asm version of this, but i haven't finished because i don't have a memory allocation function yet, and i'm really tired right now, so i'll put something up later. here's what i have so far:

dd 0x46d1e192, 0x66edf9aa, 0x927fc9e5, 0xa53baacc, 0x29b47658, 0x5a411a01
dd 0x0e66d5bd, 0x0dd5b1db, 0xcb38340e, 0x04d4ebb6, 0x98bc4f54, 0x36f20f2c
dd 0x4a3047ed, 0x1ec1e0eb, 0x568c0c1f, 0x6a731432, 0x81367fc6, 0xe3e25237
dd 0xe7f64884, 0x0fa59f64, 0x4f3109de, 0xf02d61f5, 0x5daec03b, 0x7f740e83
dd 0x056ff2d8, 0x2026cc0a, 0x7ac2112d, 0x82c55605, 0xb0911ef2, 0xa7b88e4c
dd 0x89dca282, 0x4b254d27, 0x7694a6d3, 0xd229eadd, 0x8e8f3738, 0x5bee7a55
dd 0x012eb6ab, 0x08dd28c8, 0xb5abc274, 0xbc7931f0, 0xf2396ed5, 0xe4e43d97
dd 0x943f4b7f, 0x85d0293d, 0xaed83a88, 0xc8f932fc, 0xc5496f20, 0xe9228173
dd 0x9b465b7d, 0xfda26680, 0x1ddeab35, 0x0c4f25cb, 0x86e32faf, 0xe59fa13a
dd 0xe192e2c4, 0xf147da1a, 0x67620a8d, 0x5c9a24c5, 0xfe6afde2, 0xacad0250
dd 0xd359730b, 0xf35203b3, 0x96a4b44d, 0xfbcacea6, 0x41a165ec, 0xd71e53ac
dd 0x835f39bf, 0x6b6bde7e, 0xd07085ba, 0x79064e07, 0xee5b20c3, 0x3b90bd65
dd 0x5827aef4, 0x4d12d31c, 0x9143496e, 0x6c485976, 0xd9552733, 0x220f6895
dd 0xe69def19, 0xeb89cd70, 0xc9bb9644, 0x93ec7e0d, 0x2ace3842, 0x2b6158da
dd 0x039e9178, 0xbb5367d7, 0x55682285, 0x4315d891, 0x19fd8906, 0x7d8d4448
dd 0xb4168a03, 0x40b56a53, 0xaa3e69e0, 0xa25182fe, 0xad34d16c, 0x720c4171
dd 0x9dc3b961, 0x321db563, 0x8b801b9e, 0xf5971893, 0x14cc1251, 0x8f4ae962
dd 0xf65aff1e, 0x13bd9dee, 0x5e7c78c7, 0xddb61731, 0x73832c15, 0xefebdd5b
dd 0x1f959aca, 0xe801fb22, 0xa89826ce, 0x30b7165d, 0x458a4077, 0x24fec52a
dd 0x849b065f, 0x3c6930cd, 0xa199a81d, 0xdb768f30, 0x2e45c64a, 0xff2f0d94
dd 0x4ea97917, 0x6f572acf, 0x653a195c, 0x17a88c5a, 0x27e11fb5, 0x3f09c4c1
dd 0x2f87e71b, 0xea1493e4, 0xd4b3a55e, 0xbe6090be, 0xaf6cd9d9, 0xda58ca00
dd 0x612b7034, 0x31711dad, 0x6d7db041, 0x8ca786b7, 0x09e8bf7a, 0xc3c4d7ea
dd 0xa3cd77a8, 0x7700f608, 0xdf3de559, 0x71c9353f, 0x9fd236fb, 0x1675d43e
dd 0x390d9e9a, 0x21ba4c6b, 0xbd1371e8, 0x90338440, 0xd5f163d2, 0xb140fef9
dd 0x52f50b57, 0x3710cf67, 0x4c11a79c, 0xc6d6624e, 0x3dc7afa9, 0x34a69969
dd 0x70544a26, 0xf7d9ec98, 0x7c027496, 0x1bfb3ba3, 0xb3b1dc8f, 0x9a241039
dd 0xf993f5a4, 0x15786b99, 0x26e704f7, 0x51503c04, 0x028bb3b8, 0xede5600c
dd 0x9cb22b29, 0xb6ff339b, 0x7e771c43, 0xc71c05f1, 0x604ca924, 0x695eed60
dd 0x688ed0bc, 0x3e0b232f, 0xf8a39c11, 0xbae6e67c, 0xb8cf75e1, 0x970321a7
dd 0x5328922b, 0xdef3df2e, 0x8d0443b0, 0x2885e3ae, 0x6435eed1, 0xcc375e81
dd 0xa98495f6, 0xe0bff114, 0xb2da3e4f, 0xc01b5adf, 0x507e0721, 0x6267a36a
dd 0x181a6df8, 0x7baff0c0, 0xfa6d6c13, 0x427250b2, 0xe2f742d6, 0xcd5cc723
dd 0x2d218be7, 0xb91fbbb1, 0x9eb946d0, 0x1c180810, 0xfc81d602, 0x0b9c3f52
dd 0xc2ea456f, 0x1165b2c9, 0xabf4ad75, 0x0a56fc8c, 0x12e0f818, 0xcadbcba1
dd 0x2586be56, 0x952c9b46, 0x07c6a43c, 0x78967df3, 0x477b2e49, 0x2c5d7b6d
dd 0x8a637272, 0x59acbcb4, 0x74a0e447, 0xc1f8800f, 0x35c015dc, 0x230794c2
dd 0x4405f328, 0xec2adba5, 0xd832b845, 0x6e4ed287, 0x48e9f7a2, 0xa44be89f
dd 0x38cbb725, 0xbf6ef4e6, 0xdc0e83fa, 0x54238d12, 0xf4f0c1e3, 0xa60857fd
dd 0xc43c64b9, 0x00c851ef, 0x33d75f36, 0x5fd39866, 0xd1efa08a, 0xa0640089
dd 0x877a978b, 0x99175d86, 0x57dfacbb, 0xceb02de9, 0xcf4d5c09, 0x3a8813d4
dd 0xb7448816, 0x63fa5568, 0x06be014b, 0xd642fa7b, 0x10aa7c90, 0x8082c88e
dd 0x1afcba79, 0x7519549d, 0x490a87ff, 0x8820c3a0

gencrc :
pop edi ; string object
mov ecx, [edi] ; str len
add edi, 4 ; start of str
pop eax ; hash function
mov ebx, eax
shr ebx, 8
xor al, [edi+ecx-1]
mov eax, [eax+gencrctab]
xor eax, ebx
loop gencrcloop

pop ecx ; number of entries
bsr ebx, ecx ; bsr == expensive
mov eax, 4
shl eax, ebx ; this should be the smallest power of 2 that's at least twice eax.

pop eax ; table object
pop edi ; string object
pop ebx ; value
mov ecx, [eax+4] ; number of keys
mov edx, [eax] ; table size
inc ecx

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