Aggregates with context - a question

Dear All,

I have written a STDEV aggregate function which seems to work; the only problem is that I am not sure that the method I am using was intended by the designers of aggregates.

I am using the first parameter of sfunc1 to store a pointer to a context record, and sfunc1 creates and returns that pointer when it is first called (the DB definition specified initcond1 = '0'). In this way I can accumulate all the details I need.

The problems is that the way I read the code, there is an expectation that the parameters of sfuncX and finalfunc match the basetype. This is clearly not the case, and I have declared them as int4, which will also presumable break on 64 bit implementations...

Anyway, the code is below. Any suggestions as to how I should handle complex context within aggregates would be appreciated.

Thanks,

Philip Warner.

-------------- STDEv Func:
typedef struct {
float4 ssq;
float4 s;
float4 n;
} ctx_type;

int4
sdev_ag1(int4 ctxPtr, float4 *f2)
{
ctx_type *ctx;
int4 *result;

if ((ctxPtr) == 0) {
ctx = (ctx_type*)palloc(sizeof(ctx_type));
ctx->ssq = 0;
ctx->s = 0;
ctx->n = 0;
} else {
ctx = (ctx_type*)(ctxPtr);
};

ctx->ssq += (*f2) * (*f2);
ctx->s += (*f2);
ctx->n++;

return (int4)ctx;
}

float4*
sdev_fin(int4 ctxPtr, void* p)
{
ctx_type *ctx;
float4 *result;
float4 avg;

result = (float4*)palloc(sizeof(float4));

if ((ctxPtr) == 0) {
(*result) = 0;
} else {
ctx = (ctx_type*)(ctxPtr);
avg = ctx->s / ctx->n;
(*result) = (ctx->ssq - 2*avg*ctx->s)/ctx->n + avg*avg;
(*result) = sqrt((*result));
};

pfree(ctx);

return result;
}

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