// Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.

//

// 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 <openssl/bn.h>

#include <assert.h>

#include <openssl/mem.h>

#include "internal.h"

#include "../../internal.h"

using namespace bssl;

static int bn_cmp_words_consttime(const BN_ULONG *a, size_t a_len,

                                  const BN_ULONG *b, size_t b_len) {

  static_assert(sizeof(BN_ULONG) <= sizeof(crypto_word_t),

                "crypto_word_t is too small");

  int ret = 0;

  // Process the common words in little-endian order.

  size_t min = a_len < b_len ? a_len : b_len;

  for (size_t i = 0; i < min; i++) {

    crypto_word_t eq = constant_time_eq_w(a[i], b[i]);

    crypto_word_t lt = constant_time_lt_w(a[i], b[i]);

    ret =

        constant_time_select_int(eq, ret, constant_time_select_int(lt, -1, 1));

  }

  // If `a` or `b` has non-zero words beyond `min`, they take precedence.

  if (a_len < b_len) {

    crypto_word_t mask = 0;

    for (size_t i = a_len; i < b_len; i++) {

      mask |= b[i];

    }

    ret = constant_time_select_int(constant_time_is_zero_w(mask), ret, -1);

  } else if (b_len < a_len) {

    crypto_word_t mask = 0;

    for (size_t i = b_len; i < a_len; i++) {

      mask |= a[i];

    }

    ret = constant_time_select_int(constant_time_is_zero_w(mask), ret, 1);

  }

  return ret;

}

int BN_ucmp(const BIGNUM *a, const BIGNUM *b) {

  return bn_cmp_words_consttime(a->d, a->width, b->d, b->width);

}

int BN_cmp(const BIGNUM *a, const BIGNUM *b) {

  if ((a == nullptr) || (b == nullptr)) {

    if (a != nullptr) {

      return -1;

    } else if (b != nullptr) {

      return 1;

    } else {

      return 0;

    }

  }

  // We do not attempt to process the sign bit in constant time. Negative

  // `BIGNUM`s should never occur in crypto, only calculators.

  if (a->neg != b->neg) {

    if (a->neg) {

      return -1;

    }

    return 1;

  }

  int ret = BN_ucmp(a, b);

  return a->neg ? -ret : ret;

}

int bssl::bn_less_than_words(const BN_ULONG *a, const BN_ULONG *b, size_t len) {

  return bn_cmp_words_consttime(a, len, b, len) < 0;

}

int BN_abs_is_word(const BIGNUM *bn, BN_ULONG w) {

  if (bn->width == 0) {

    return w == 0;

  }

  BN_ULONG mask = bn->d[0] ^ w;

  for (int i = 1; i < bn->width; i++) {

    mask |= bn->d[i];

  }

  return mask == 0;

}

int BN_cmp_word(const BIGNUM *a, BN_ULONG b) {

  BIGNUM b_bn;

  BN_init(&b_bn);

  b_bn.d = &b;

  b_bn.width = b > 0;

  b_bn.dmax = 1;

  b_bn.flags = BN_FLG_STATIC_DATA;

  return BN_cmp(a, &b_bn);

}

int BN_is_zero(const BIGNUM *bn) {

  return bn_fits_in_words(bn, 0);

}

int BN_is_one(const BIGNUM *bn) {

  return bn->neg == 0 && BN_abs_is_word(bn, 1);

}

int BN_is_word(const BIGNUM *bn, BN_ULONG w) {

  return BN_abs_is_word(bn, w) && (w == 0 || bn->neg == 0);

}

int BN_is_odd(const BIGNUM *bn) {

  return bn->width > 0 && (bn->d[0] & 1) == 1;

}

int BN_is_pow2(const BIGNUM *bn) {

  int width = bn_minimal_width(bn);

  if (width == 0 || bn->neg) {

    return 0;

  }

  for (int i = 0; i < width - 1; i++) {

    if (bn->d[i] != 0) {

      return 0;

    }

  }

  return 0 == (bn->d[width-1] & (bn->d[width-1] - 1));

}

int BN_equal_consttime(const BIGNUM *a, const BIGNUM *b) {

  BN_ULONG mask = 0;

  // If `a` or `b` has more words than the other, all those words must be zero.

  for (int i = a->width; i < b->width; i++) {

    mask |= b->d[i];

  }

  for (int i = b->width; i < a->width; i++) {

    mask |= a->d[i];

  }

  // Common words must match.

  int min = a->width < b->width ? a->width : b->width;

  for (int i = 0; i < min; i++) {

    mask |= (a->d[i] ^ b->d[i]);

  }

  // The sign bit must match.

  mask |= (a->neg ^ b->neg);

  return mask == 0;

}