Function tdigest_add_double

pg_documentdb/src/aggregation/bson_tdigest.c:675–751

* Add a value to the tdigest (create one if needed). Transition function * for tdigest aggregate with a single percentile. */

 * for tdigest aggregate with a single percentile.
 */
Datum
tdigest_add_double(PG_FUNCTION_ARGS)
{
	tdigest_aggstate_t *state;

	MemoryContext aggcontext;

	/* cannot be called directly because of internal-type argument */
	if (!AggCheckCallContext(fcinfo, &aggcontext))
	{
		elog(ERROR, "tdigest_add_double called in non-aggregate context");
	}

	/*
	 * We want to skip NULL values altogether - we return either the existing
	 * t-digest (if it already exists) or NULL.
	 */
	if (PG_ARGISNULL(1))
	{
		if (PG_ARGISNULL(0))
		{
			PG_RETURN_NULL();
		}

		/* if there already is a state accumulated, don't forget it */
		PG_RETURN_DATUM(PG_GETARG_DATUM(0));
	}

	/* if there's no digest allocated, create it now */
	if (PG_ARGISNULL(0))
	{
		int compression = PG_GETARG_INT32(2);
		int npercentiles = 1;
		MemoryContext oldcontext;

		check_compression(compression);

		oldcontext = MemoryContextSwitchTo(aggcontext);

		pgbson *percentilesPgbson = PG_GETARG_MAYBE_NULL_PGBSON(3);
		if (percentilesPgbson == NULL || IsPgbsonEmptyDocument(percentilesPgbson))
		{
			PG_RETURN_NULL();
		}
		pgbsonelement percentilesPgbsonElement;
		PgbsonToSinglePgbsonElement(percentilesPgbson, &percentilesPgbsonElement);
		double percentile = percentilesPgbsonElement.bsonValue.value.v_double;

		state = tdigest_aggstate_allocate(npercentiles, 0, compression);

		state->percentiles[0] = percentile;

		MemoryContextSwitchTo(oldcontext);
	}
	else
	{
		state = (tdigest_aggstate_t *) PG_GETARG_POINTER(0);
	}