/**************************************************************************** * 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> #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 */ }; const char *str_alloc( const char *str ); char *quick_link( char *str ); int str_free( char *str ); 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. */ const char *str_alloc( const 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. */ const char *quick_link( const 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. String = %s\n", str ); 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( const 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; } bool in_hash_table( const 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 && str == ( ( char * )ptr + psize ) ) return true; return false; }