Function normal_rand

contrib/tablefunc/tablefunc.c:171–269

 */
PG_FUNCTION_INFO_V1(normal_rand);
Datum
normal_rand(PG_FUNCTION_ARGS)
{
	FuncCallContext *funcctx;
	uint64		call_cntr;
	uint64		max_calls;
	normal_rand_fctx *fctx;
	float8		mean;
	float8		stddev;
	float8		carry_val;
	bool		use_carry;
	MemoryContext oldcontext;

	/* stuff done only on the first call of the function */
	if (SRF_IS_FIRSTCALL())
	{
		int32		num_tuples;

		/* 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);

		/* total number of tuples to be returned */
		num_tuples = PG_GETARG_INT32(0);
		if (num_tuples < 0)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
					 errmsg("number of rows cannot be negative")));
		funcctx->max_calls = num_tuples;

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

		/*
		 * Use fctx to keep track of upper and lower bounds from call to call.
		 * It will also be used to carry over the spare value we get from the
		 * Box-Muller algorithm so that we only actually calculate a new value
		 * every other call.
		 */
		fctx->mean = PG_GETARG_FLOAT8(1);
		fctx->stddev = PG_GETARG_FLOAT8(2);
		fctx->carry_val = 0;
		fctx->use_carry = false;

		funcctx->user_fctx = fctx;

		MemoryContextSwitchTo(oldcontext);
	}

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

	call_cntr = funcctx->call_cntr;
	max_calls = funcctx->max_calls;