/**************************************************************************** * Advanced string hashing functions (c)1996 D.S.D. Software, written by * * Derek Snider for use in SMAUG. * * * * These functions keep track of how many "links" are pointing to the * * memory allocated, and will free the memory if all the links are removed. * * Make absolutely sure you do not mix use of strdup and free with these * * functions, or nasty stuff will happen! * * Most occurances of strdup/str_dup should be replaced with str_alloc, and * * any free/DISPOSE used on the same pointer should be replaced with * * str_free. If a function uses strdup for temporary use... it is best if * * it is left as is. Just don't get usage mixed up between conventions. * * The hashstr_data size is 8 bytes of overhead. Don't be concerned about * * this as you still save lots of space on duplicate strings. -Thoric * ****************************************************************************/ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #define STR_HASH_SIZE 1024 struct hashstr_data { struct hashstr_data *next; /* next hash element */ unsigned short int links; /* number of links to this string */ unsigned short int length; /* length of string */ }; char *str_alloc( char *str ); char *quick_link( char *str ); int str_free( char *str ); void show_hash( int count ); char *hash_stats( void ); struct hashstr_data *string_hash[STR_HASH_SIZE]; /* * Check hash table for existing occurance of string. * If found, increase link count, and return pointer, * otherwise add new string to hash table, and return pointer. */ char *str_alloc( char *str ) { register int len, hash, psize; register struct hashstr_data *ptr; len = strlen( str ); psize = sizeof( struct hashstr_data ); hash = len % STR_HASH_SIZE; for( ptr = string_hash[hash]; ptr; ptr = ptr->next ) if( len == ptr->length && !strcmp( str, ( char * )ptr + psize ) ) { if( ptr->links < 65535 ) ++ptr->links; return ( char * )ptr + psize; } ptr = ( struct hashstr_data * )malloc( len + psize + 1 ); ptr->links = 1; ptr->length = len; if( len ) strcpy( ( char * )ptr + psize, str ); /* memcpy( (char *) ptr+psize, str, len+1 ); */ else strcpy( ( char * )ptr + psize, "" ); ptr->next = string_hash[hash]; string_hash[hash] = ptr; return ( char * )ptr + psize; } /* * Used to make a quick copy of a string pointer that is known to be already * in the hash table. Function increments the link count and returns the * same pointer passed. */ char *quick_link( char *str ) { register struct hashstr_data *ptr; ptr = ( struct hashstr_data * )( str - sizeof( struct hashstr_data ) ); if( ptr->links == 0 ) { fprintf( stderr, "quick_link: bad pointer\n" ); return NULL; } if( ptr->links < 65535 ) ++ptr->links; return str; } /* * Used to remove a link to a string in the hash table. * If all existing links are removed, the string is removed from the * hash table and disposed of. * returns how many links are left, or -1 if an error occurred. */ int str_free( char *str ) { register int len, hash; register struct hashstr_data *ptr, *ptr2, *ptr2_next; len = strlen( str ); hash = len % STR_HASH_SIZE; ptr = ( struct hashstr_data * )( str - sizeof( struct hashstr_data ) ); if( ptr->links == 65535 ) /* permanent */ return ptr->links; if( ptr->links == 0 ) { fprintf( stderr, "str_free: bad pointer\n" ); return -1; } if( --ptr->links == 0 ) { if( string_hash[hash] == ptr ) { string_hash[hash] = ptr->next; free( ptr ); return 0; } for( ptr2 = string_hash[hash]; ptr2; ptr2 = ptr2_next ) { ptr2_next = ptr2->next; if( ptr2_next == ptr ) { ptr2->next = ptr->next; free( ptr ); return 0; } } fprintf( stderr, "str_free: pointer not found for string: %s\n", str ); return -1; } return ptr->links; } void show_hash( int count ) { struct hashstr_data *ptr; int x, c; for( x = 0; x < count; x++ ) { for( c = 0, ptr = string_hash[x]; ptr; ptr = ptr->next, c++ ); fprintf( stderr, " %d", c ); } fprintf( stderr, "\n" ); } void hash_dump( int hash ) { struct hashstr_data *ptr; char *str; int c, psize; if( hash > STR_HASH_SIZE || hash < 0 ) { fprintf( stderr, "hash_dump: invalid hash size\n\r" ); return; } psize = sizeof( struct hashstr_data ); for( c = 0, ptr = string_hash[hash]; ptr; ptr = ptr->next, c++ ) { str = ( char * )( ( ( int )ptr ) + psize ); fprintf( stderr, "Len:%4d Lnks:%5d Str: %s\n\r", ptr->length, ptr->links, str ); } fprintf( stderr, "Total strings in hash %d: %d\n\r", hash, c ); } char *check_hash( char *str ) { static char buf[1024]; int len, hash, psize, p = 0, c; struct hashstr_data *ptr, *fnd; buf[0] = '\0'; len = strlen( str ); psize = sizeof( struct hashstr_data ); hash = len % STR_HASH_SIZE; for( fnd = NULL, ptr = string_hash[hash], c = 0; ptr; ptr = ptr->next, c++ ) if( len == ptr->length && !strcmp( str, ( char * )ptr + psize ) ) { fnd = ptr; p = c + 1; } if( fnd ) sprintf( buf, "Hash info on string: %s\n\rLinks: %d Position: %d/%d Hash: %d Length: %d\n\r", str, fnd->links, p, c, hash, fnd->length ); else sprintf( buf, "%s not found.\n\r", str ); return buf; } char *hash_stats( void ) { static char buf[1024]; struct hashstr_data *ptr; int x, c, total, totlinks, unique, bytesused, wouldhave, hilink; totlinks = unique = total = bytesused = wouldhave = hilink = 0; for( x = 0; x < STR_HASH_SIZE; x++ ) { for( c = 0, ptr = string_hash[x]; ptr; ptr = ptr->next, c++ ) { total++; if( ptr->links == 1 ) unique++; if( ptr->links > hilink ) hilink = ptr->links; totlinks += ptr->links; bytesused += ( ptr->length + 1 + sizeof( struct hashstr_data ) ); wouldhave += ( ptr->links * ( ptr->length + 1 ) ); } } sprintf( buf, "Hash strings allocated:%8d Total links : %d\n\rString bytes allocated:%8d Bytes saved : %d\n\rUnique (wasted) links :%8d Hi-Link count: %d\n\r", total, totlinks, bytesused, wouldhave - bytesused, unique, hilink ); return buf; } void show_high_hash( int top ) { struct hashstr_data *ptr; int x, psize; char *str; psize = sizeof( struct hashstr_data ); for( x = 0; x < STR_HASH_SIZE; x++ ) for( ptr = string_hash[x]; ptr; ptr = ptr->next ) if( ptr->links >= top ) { str = ( char * )( ( ( int )ptr ) + psize ); fprintf( stderr, "Links: %5d String: >%s<\n\r", ptr->links, str ); } }