Collation Callback Functions

When mco_register_collations() or mco_uda_register_collation() is called it must pass a mco_collation_funcs_t structure containing two callback functions defined as follows:

 
    typedef struct mco_collation_funcs_t_ 
    {
        mco_compare_collation_f comp;
        mco_hash_collation_f    hash;
    } mco_collation_funcs_t, *mco_collation_funcs_h;
     

The collation compare functions have the following prototype defined in mco.h:

     
    typedef int2 (*mco_compare_collation_f) ( mco_collate_h c1, uint2 len1, mco_collate_h c2, uint2 len2);
     

The parameters are as follows:

c1	The address of the first mco_collate_t struct used for the comparison.
len1	The length of the first operand in the comparison.
c2	The address of the second mco_collate_t struct used for the comparison.
len2	The length of the second operand in the comparison.

Note that the compare functions should return < 0, =, or >0 depending on whether the object value is less than, equal to or greater than the external key value.

The collation hash functions have the following prototype defined in mco.h:

     
    typedef mco_hash_counter_t (*mco_hash_collation_f) ( mco_collate_h c, uint2 len);
     

The parameters are as follows:

c	The address of the mco_collate_t struct containing the character array to hash.
len	The length of the character array to hash.

 

Following are examples of collation function implementations:

 
    /* custom compare & hash functions */
    int2 coll_cmp(mco_collate_h c1, uint2 len1, mco_collate_h c2, uint2 len2)
    {
        mco_uda_value_t val1, val2;
        char buf1[20], buf2[20];
         
        /* get first object's value */
        val1.type = MCO_DD_STRING;
        val1.v.p.size = sizeof(buf1);
        val1.v.p.p.c = buf1;
        mco_uda_collate_get(c1, &val1);
         
        /* get second object's value */
        val2.type = MCO_DD_STRING;
        val2.v.p.size = sizeof(buf2);
        val2.v.p.p.c = buf2;
        mco_uda_collate_get(c2, &val2);
         
        /* compare values */
        return STR_CMP(buf1, buf2);
    }
     
    uint4 coll_hash(mco_collate_h c, uint2 len)
    {
        mco_uda_value_t val;
        char buf[20];
         
        /* get object's value */
        val.type = MCO_DD_STRING;
        val.v.p.size = sizeof(buf);
        val.v.p.p.c = buf;
        mco_uda_collate_get(c, &val);
         
        /* hash value */
        return strlen(buf);
    }