/*
// Copyright (c) 2010-2017 Intel Corporation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
*/

#include <stdlib.h>
#include <inttypes.h>

#include <rte_cycles.h>

#include "prox_malloc.h"
#include "cdf.h"

static uint32_t round_pow2(uint32_t val)
{
	uint32_t ret;
	uint32_t s = 1 << 31;

	while ((s & val) == 0)
		s = s >> 1;
	if (s == 1U << 31 && s != val)
		return 0;

	ret = val;
	if (s != ret)
		ret = (s << 1);

	return ret;
}

static uint32_t get_r_max(struct cdf *cdf, uint32_t cur)
{
	uint32_t right_child = cur;

	do {
		cur = right_child;
		right_child = cur * 2 + 1;
	} while (right_child < cdf->elems[0]);

	return cdf->elems[cur];
}

struct cdf *cdf_create(uint32_t n_vals, int socket_id)
{
	struct cdf *ret;
	size_t mem_size = 0;
	uint32_t n_vals_round = round_pow2(n_vals);

	if (0 == n_vals_round)
		return NULL;

	mem_size += sizeof(struct cdf);
	mem_size += sizeof(((struct cdf *)(0))->elems[0]) * n_vals_round * 2;
	ret = prox_zmalloc(mem_size, socket_id);
	ret->elems[0] = n_vals;

	/* leafs are [n_vals, 2 * n_vals[. During cdf_add() and
	   cdf_setup(), rand_max refers to the index of the next leaf
	   to be added.  */
	ret->rand_max = n_vals_round;
	ret->first_child = n_vals_round;
	ret->seed = rte_rdtsc();

	return ret;
}

void cdf_add(struct cdf *cdf, uint32_t len)
{
	cdf->elems[cdf->rand_max++] = len;
}

int cdf_setup(struct cdf *cdf)
{
	uint32_t last_leaf, first_leaf;
	uint32_t first_parent, last_parent;
	uint32_t total, multiplier, cur, end;

	if (cdf->elems[0] == 1) {
		cdf->rand_max = RAND_MAX;
		cdf->elems[1] = RAND_MAX;
		cdf->elems[0] = 2;
		return 0;
	}

	last_leaf  = cdf->rand_max;
	first_leaf = round_pow2(cdf->elems[0]);
	/* Failed to add all elements through cdf_add() */
	if (last_leaf - first_leaf != cdf->elems[0])
		return -1;

	total = 0;
	for (uint32_t i = first_leaf; i < last_leaf; ++i) {
		total += cdf->elems[i];
	}

	multiplier = RAND_MAX / total;
	if (multiplier * total == RAND_MAX)
		multiplier--;
	cdf->rand_max = multiplier * total;
	total = 0;
	for (uint32_t i = first_leaf; i < last_leaf; ++i) {
		uint32_t cur = cdf->elems[i];

		/* Each element represents the range between previous
		   total (non-inclusive) and new total (inclusive). */
		total += cur * multiplier - 1;
		cdf->elems[i] = total;
		total += 1;
	}
	end = round_pow2(first_leaf) << 1;
	for (uint32_t i = last_leaf; i < end; ++i) {
		cdf->elems[i] = RAND_MAX;
	}
	cdf->first_child = first_leaf;
	cdf->elems[0] = end;

	/* Build the binary tree used at run-time. */
	last_leaf = end - 1;
	do {
		first_parent = first_leaf/2;
		last_parent  = last_leaf/2;

		for (uint32_t i = first_parent; i <= last_parent; ++i) {
			/* The current nodes value should be the
			   biggest value accessible through its left
			   child. This value is stored in the right
			   most child of the left child. The left most
			   child of the right child is the first value
			   that can not be accessed through the left
			   child.  */
			cdf->elems[i] = get_r_max(cdf, i * 2);
		}
		first_leaf = first_parent;
		last_leaf = last_parent;
	} while (first_parent != last_parent);
	return 0;
}