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
amusing 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
pointerwhen it is first called (the DB definition specified initcond1 = '0'). In this way I can accumulate all the
detailsI need.
 

The problems is that the way I read the code, there is an expectation that the parameters of sfuncX and finalfunc match
thebasetype. 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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