/*

* Copyright 2018 Google LLC

*

* 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

*

* https://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 <stdint.h>

#include <algorithm>

#include "randbelow.h"

static inline void cardchoose(uint32_t n, uint32_t k, uint32_t* result) {

auto t = n - k + 1;

for (uint32_t i = 0; i < k; i++) {

uint32_t r = randbelow(t + i);

if (r < t) {

result[i] = r;

} else {

result[i] = result[r - t];

}

}

std::sort(result, result + k);

}

extern "C" void sorted_cardchoose(uint32_t n, uint32_t k, uint32_t* result) {

cardchoose(n, k, result);

for (uint32_t i = 0; i < k; i++) {

result[i] += i;

}

}

extern "C" void random_cardchoose(uint32_t n, uint32_t k, uint32_t* result) {

cardchoose(n, k, result);

for (uint32_t i = 0; i < k; i++) {

uint32_t r = randbelow(i + 1);

auto t = result[i] + i;

result[i] = result[r];

result[r] = t;

}

}