Function svec_unnest

methods/svec_util/src/pg_gp/svec_util.c:97–178

 */
PG_FUNCTION_INFO_V1(svec_unnest);
Datum svec_unnest(PG_FUNCTION_ARGS)
{
        FuncCallContext *funcctx;
        svec_unnest_fctx *fctx;
        MemoryContext oldcontext;
	float8 result;
	SvecType *svec;
	int run_length=0;

        /* stuff done only on the first call of the function */
        if (SRF_IS_FIRSTCALL())
        {
                /* create a function context for cross-call persistence */
                funcctx = SRF_FIRSTCALL_INIT();

                /* switch to memory context appropriate for multiple
		 * function calls
                 */
                oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

                /* allocate memory for user context */
                fctx = (svec_unnest_fctx *)
			palloc(sizeof(svec_unnest_fctx));

		svec   = PG_GETARG_SVECTYPE_P(0);
		fctx->sdata = sdata_from_svec(svec);

		/* set initial index into the sparse vector argument */
		fctx->dimension               = svec->dimension;
		if (fctx->dimension == -1) fctx->dimension = 1;
		fctx->absolute_value_position = 0;
		fctx->unique_value_position   = 0;
		fctx->index_position          = fctx->sdata->index->data;
		fctx->run_position            = 1;

                funcctx->user_fctx = fctx;

                MemoryContextSwitchTo(oldcontext);
        }

        /* stuff done on every call of the function */
	funcctx = SRF_PERCALL_SETUP();

        fctx = funcctx->user_fctx;

	run_length = compword_to_int8(fctx->index_position);

	if (fctx->dimension > fctx->absolute_value_position)
	{
		result = ((float8 *)(fctx->sdata->vals->data))
			[fctx->unique_value_position];

		fctx->absolute_value_position++;
		fctx->run_position++;
		if (fctx->run_position > run_length)
		{
			fctx->run_position = 1;
			fctx->unique_value_position++;