backend dies on my aggregate function in 7.1.2

Hi,

I am trying to write an aggregate function (maxalphanum_check) for
7.1.2 but I just get abnormal termination of the backend. It uses a
function maxalphanum_gt which works quite well alone. What am I doing
wrong?

*** this is the aggregate function:

#include <postgres.h>

text * maxalphanum_check(text *internal, text *next) {
text *new, *new_t;

if (maxalphanum_gt(next, internal)) {
new = next;
} else {
new = internal;
}

/* it seems that we must allocate the value we return */

new_t = (text *) palloc(VARSIZE(new));
memset(new_t, 0, VARSIZE(new));
VARATT_SIZEP(new_t) = VARSIZE(new);
memcpy((void *) VARDATA(new_t),
(void *) VARDATA(new),
VARSIZE(new)-VARHDRSZ);

return(new_t);
}

*** compiled by

gcc -O -fPIC -I../../postgresql-7.1.2/src/include -c maxalphanum.c
gcc -shared -o maxalphanum.so maxalphanum.o

*** the aggregate is then created by

CREATE AGGREGATE maxalphanum (
SFUNC1 = maxalphanum_check,
BASETYPE = TEXT,
STYPE1 = TEXT
);

*** the query which breaks the backend is then eg:

SELECT maxalphanum(x) FROM t GROUP BY x;
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

*** This is the function maxalphanum_gt which works quite well in
selects:

/*
a state transition function for the maxalphanum aggregate
*/

#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#include <postgres.h>

#define MAXLEN 256

int maxalphanum_gt(text *str_a, text *str_b) {
char *a_data = (char *) VARDATA(str_a);
char *b_data = (char *) VARDATA(str_b);

char a_str[MAXLEN];
char b_str[MAXLEN];

int a_len = VARSIZE(str_a) - VARHDRSZ;
int b_len = VARSIZE(str_b) - VARHDRSZ;

char a = a_data[0];
char b = b_data[0];

if (a_len == 0 && b_len > 0) {
return 0;
}

if (a_len > 0 && b_len == 0) {
return 1;
}

if (a_len >= MAXLEN || b_len >= MAXLEN) {
return 0;
}

memcpy(a_str, a_data, a_len);
a_str[a_len] = '\0';

memcpy(b_str, b_data, b_len);
b_str[b_len] = '\0';

if (isdigit(a) && isdigit(b)) {
return atoi(a_str) > atoi(b_str);
}

if (isdigit(a) && isalpha(b)) {
return 1;
}

if (isalpha(a) && isdigit(b)) {
return 0;
}

if (isalpha(a) && isalpha(b)) {
return strcasecmp(a_str, b_str) > 0;
}

return a > b;
}

Dirk