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Block header

fsHashTable is the structure of a HashTable block. It functions much like the hash table found in FFS user directory blocks, except that it is stored in a seperate block. This block contains a number of hash-chains (about 120 for a 512 byte block). Each hash-chain is a chain of Nodes. Each Node has a pointer to an Object and a pointer to the next entry in the hash-chain.  Using such a hash-chain you can locate an object quickly by only knowing its name.

Field Type Description
bheader struct fsBlockHeader Standard block header.
parent NODE The node number of the directory Object this HashTable block belongs to.
hashentry NODE An array of Nodes.  Each Node represents the start of a hash-chain (singly linked).  A hash-value is calculated using the name of a file or directory, and this value determines in which chain the Object is linked.  If there are no entries in a hash-chain then the hashentry value is zero.
struct fsHashTable {
    struct fsBlockHeader bheader;
    NODE parent;
    NODE hashentry[0];

To calculate the hash-value using a name of an Object as input use these routines:

UWORD calchash(UBYTE *name) {
    UWORD hash=0;
    /* Calculates a hash value over the passed in string.
       The end of the string can be either a NUL byte or a
       slash. The hash function is the same as the one
       used in FastFileSystem set to international mode. */
    while(name[hash]!=0 && name[hash]!='/') {
    while(*name!=0 && *name!='/') {

    return((UWORD)(hash % (UWORD)((blocksize-sizeof(struct fsHashTable))>>2)));
UBYTE upperchar(UBYTE c) {
    if((c>=224 && c<=254 && c!=247) || (c>='a' && c<='z')) {

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For comments, problems or questions regarding this page contact John Hendrikx.
Last updated: 17 oktober 1998.