Example: my_bit_xor Definition

The aggregate UDF my_bit_xor example is similar to the SA built-in BIT_XOR, except my_bit_xor operates only on unsigned integers.
my_bit_xor definition

Because the input and the output data types are identical, use the normal _next_value_extfn and _evaluate_extfn functions to accumulate subaggregate values and produce the superaggregate result.
#include "extfnapiv4.h"
#include <stdlib.h>
#include <assert.h>


//  Generic aggregate UDF that exclusive-ORs a set of 
//  unsigned integer arguments, and whenever asked
//  returns the resulting unsigned integer result.
//
//  The start function creates a little structure for
//  the running result, and the finish function then
//  deallocates it.
//
//  Since there are no aggregate usage restrictions 
//  for this aggregate UDF, the corresponding SQL declaration
//  will look like:
//
//              CREATE AGGREGATE FUNCTION my_bit_xor(IN arg1 UNSIGNED INT) 
//                      RETURNS UNSIGNED INT
//                      ON EMPTY INPUT RETURNS NULL
//                      EXTERNAL NAME 'my_bit_xor@libudfex'


typedef struct my_xor_result {
  a_sql_uint64 _num_nonnulls_seen;
  a_sql_uint32 _xor_result;
} my_xor_result;

#if defined __cplusplus
extern "C" {
#endif

static void my_xor_start(a_v3_extfn_aggregate_context *cntxt)
{
}


static void my_xor_finish(a_v3_extfn_aggregate_context *cntxt)
{
}


static void my_xor_reset(a_v3_extfn_aggregate_context *cntxt)
{
  my_xor_result *cptr = (my_xor_result *)cntxt->_user_calculation_context;
  cptr->_xor_result = 0;
  cptr->_num_nonnulls_seen = 0;
}


static void my_xor_next_value(a_v3_extfn_aggregate_context *cntxt, 
                              void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_uint32 arg1;

  my_xor_result *cptr = (my_xor_result *)cntxt->_user_calculation_context;

  //  Get the one argument, and add it to the total
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_uint32 *)arg.data);
    cptr->_xor_result ^= arg1;
    cptr->_num_nonnulls_seen++;
  }
}


static void my_xor_drop_value(a_v3_extfn_aggregate_context *cntxt, 
                              void *arg_handle)
{
  an_extfn_value  arg;
  a_sql_uint32 arg1;
  my_xor_result *cptr = (my_xor_result *)cntxt->_user_calculation_context;

  //  Get the one argument, and remove it from the total
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_uint32 *)arg.data);
    cptr->_xor_result ^= arg1;
    cptr->_num_nonnulls_seen--;
  }
}


static void my_xor_evaluate(a_v3_extfn_aggregate_context *cntxt, 
                            void *arg_handle)
{
  an_extfn_value  outval;
  my_xor_result *cptr = (my_xor_result *)cntxt->_user_calculation_context;

  outval.type = DT_UNSINT;
  outval.piece_len = sizeof(a_sql_uint32);
  if (cptr->_num_nonnulls_seen > 0) {
    outval.data = &cptr->_xor_result;
  } else {
    outval.data = 0;
  }
  cntxt->set_value( arg_handle, &outval, 0 );
}


static void my_xor_cum_evaluate(a_v3_extfn_aggregate_context *cntxt, 
                                void *arg_handle)
{
  an_extfn_value  outval;
  an_extfn_value  arg;
  a_sql_uint32 arg1;
  my_xor_result *cptr = (my_xor_result *)cntxt->_user_calculation_context;

  //  Get the one argument, and include it in the result,
  //  unless that input value is null.
  //
  if (cntxt->get_value( arg_handle, 1, &arg) && arg.data) {
    arg1 = *((a_sql_uint32 *)arg.data);
    cptr->_xor_result ^= arg1;
    cptr->_num_nonnulls_seen++;
  }

  //  Then set the output result value
  outval.type = DT_UNSINT;
  outval.piece_len = sizeof(a_sql_uint32);
  if (cptr->_num_nonnulls_seen > 0) {
    outval.data = &cptr->_xor_result;
  } else {
    outval.data = 0;
  }
  cntxt->set_value( arg_handle, &outval, 0 );
}


static a_v3_extfn_aggregate my_xor_descriptor = 
    {
        &my_xor_start, 
        &my_xor_finish,
        &my_xor_reset,
        &my_xor_next_value,
        &my_xor_evaluate,
        &my_xor_drop_value,
        &my_xor_cum_evaluate,
        &my_xor_next_value,
        &my_xor_drop_value,
        &my_xor_evaluate,
        NULL, // reserved1_must_be_null
        NULL, // reserved2_must_be_null
        NULL, // reserved3_must_be_null
        NULL, // reserved4_must_be_null
        NULL, // reserved5_must_be_null
        0,    // indicators
        ( short )sizeof( my_xor_result ), // context size
        8,    // context alignment
        0.0,  // external_bytes_per_group 
        0.0,  // external bytes per row
        0,    // reserved6_must_be_null
        0,    // reserved7_must_be_null
        0,    // reserved8_must_be_null
        0,    // reserved9_must_be_null
        0,    // reserved10_must_be_null
        NULL  // _for_server_internal_use
    };

a_v3_extfn_aggregate *my_bit_xor()
{
  return &my_xor_descriptor;
}

#if defined __cplusplus
}
#endif