// 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 <string.h>

#include <openssl/err.h>

#include "internal.h"

int BN_lshift(BIGNUM *r, const BIGNUM *a, int n) {

  int i, nw, lb, rb;

  BN_ULONG *t, *f;

  BN_ULONG l;

  if (n < 0) {

    OPENSSL_PUT_ERROR(BN, BN_R_NEGATIVE_NUMBER);

    return 0;

  }

  r->neg = a->neg;

  nw = n / BN_BITS2;

  if (!bn_wexpand(r, a->width + nw + 1)) {

    return 0;

  }

  lb = n % BN_BITS2;

  rb = BN_BITS2 - lb;

  f = a->d;

  t = r->d;

  t[a->width + nw] = 0;

  if (lb == 0) {

    for (i = a->width - 1; i >= 0; i--) {

      t[nw + i] = f[i];

    }

  } else {

    for (i = a->width - 1; i >= 0; i--) {

      l = f[i];

      t[nw + i + 1] |= l >> rb;

      t[nw + i] = l << lb;

    }

  }

  OPENSSL_memset(t, 0, nw * sizeof(t[0]));

  r->width = a->width + nw + 1;

  bn_set_minimal_width(r);

  return 1;

}

int BN_lshift1(BIGNUM *r, const BIGNUM *a) {

  BN_ULONG *ap, *rp, t, c;

  int i;

  if (r != a) {

    r->neg = a->neg;

    if (!bn_wexpand(r, a->width + 1)) {

      return 0;

    }

    r->width = a->width;

  } else {

    if (!bn_wexpand(r, a->width + 1)) {

      return 0;

    }

  }

  ap = a->d;

  rp = r->d;

  c = 0;

  for (i = 0; i < a->width; i++) {

    t = *(ap++);

    *(rp++) = (t << 1) | c;

    c = t >> (BN_BITS2 - 1);

  }

  if (c) {

    *rp = 1;

    r->width++;

  }

  return 1;

}

void bn_rshift_words(BN_ULONG *r, const BN_ULONG *a, unsigned shift,

                     size_t num) {

  unsigned shift_bits = shift % BN_BITS2;

  size_t shift_words = shift / BN_BITS2;

  if (shift_words >= num) {

    OPENSSL_memset(r, 0, num * sizeof(BN_ULONG));

    return;

  }

  if (shift_bits == 0) {

    OPENSSL_memmove(r, a + shift_words, (num - shift_words) * sizeof(BN_ULONG));

  } else {

    for (size_t i = shift_words; i < num - 1; i++) {

      r[i - shift_words] =

          (a[i] >> shift_bits) | (a[i + 1] << (BN_BITS2 - shift_bits));

    }

    r[num - 1 - shift_words] = a[num - 1] >> shift_bits;

  }

  OPENSSL_memset(r + num - shift_words, 0, shift_words * sizeof(BN_ULONG));

}

int BN_rshift(BIGNUM *r, const BIGNUM *a, int n) {

  if (n < 0) {

    OPENSSL_PUT_ERROR(BN, BN_R_NEGATIVE_NUMBER);

    return 0;

  }

  if (!bn_wexpand(r, a->width)) {

    return 0;

  }

  bn_rshift_words(r->d, a->d, n, a->width);

  r->neg = a->neg;

  r->width = a->width;

  bn_set_minimal_width(r);

  return 1;

}

int bn_rshift_secret_shift(BIGNUM *r, const BIGNUM *a, unsigned n,

                           BN_CTX *ctx) {

  bssl::BN_CTXScope scope(ctx);

  BIGNUM *tmp = BN_CTX_get(ctx);

  unsigned max_bits;

  if (tmp == NULL || !BN_copy(r, a) || !bn_wexpand(tmp, r->width)) {

    return 0;

  }

  // Shift conditionally by powers of two.

  max_bits = BN_BITS2 * r->width;

  for (unsigned i = 0; (max_bits >> i) != 0; i++) {

    BN_ULONG mask = (n >> i) & 1;

    mask = 0 - mask;

    bn_rshift_words(tmp->d, r->d, 1u << i, r->width);

    bn_select_words(r->d, mask, tmp->d /* apply shift */,

                    r->d /* ignore shift */, r->width);

  }

  return 1;

}

void bn_rshift1_words(BN_ULONG *r, const BN_ULONG *a, size_t num) {

  if (num == 0) {

    return;

  }

  for (size_t i = 0; i < num - 1; i++) {

    r[i] = (a[i] >> 1) | (a[i + 1] << (BN_BITS2 - 1));

  }

  r[num - 1] = a[num - 1] >> 1;

}

int BN_rshift1(BIGNUM *r, const BIGNUM *a) {

  if (!bn_wexpand(r, a->width)) {

    return 0;

  }

  bn_rshift1_words(r->d, a->d, a->width);

  r->width = a->width;

  r->neg = a->neg;

  bn_set_minimal_width(r);

  return 1;

}

int BN_set_bit(BIGNUM *a, int n) {

  if (n < 0) {

    return 0;

  }

  int i = n / BN_BITS2;

  int j = n % BN_BITS2;

  if (a->width <= i) {

    if (!bn_wexpand(a, i + 1)) {

      return 0;

    }

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

      a->d[k] = 0;

    }

    a->width = i + 1;

  }

  a->d[i] |= (((BN_ULONG)1) << j);

  return 1;

}

int BN_clear_bit(BIGNUM *a, int n) {

  int i, j;

  if (n < 0) {

    return 0;

  }

  i = n / BN_BITS2;

  j = n % BN_BITS2;

  if (a->width <= i) {

    return 0;

  }

  a->d[i] &= (~(((BN_ULONG)1) << j));

  bn_set_minimal_width(a);

  return 1;

}

int bn_is_bit_set_words(const BN_ULONG *a, size_t num, size_t bit) {

  size_t i = bit / BN_BITS2;

  size_t j = bit % BN_BITS2;

  if (i >= num) {

    return 0;

  }

  return (a[i] >> j) & 1;

}

int BN_is_bit_set(const BIGNUM *a, int n) {

  if (n < 0) {

    return 0;

  }

  return bn_is_bit_set_words(a->d, a->width, n);

}

int BN_mask_bits(BIGNUM *a, int n) {

  if (n < 0) {

    return 0;

  }

  int w = n / BN_BITS2;

  int b = n % BN_BITS2;

  if (w >= a->width) {

    return 1;

  }

  if (b == 0) {

    a->width = w;

  } else {

    a->width = w + 1;

    a->d[w] &= ~(BN_MASK2 << b);

  }

  bn_set_minimal_width(a);

  return 1;

}

static int bn_count_low_zero_bits_word(BN_ULONG l) {

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

                "crypto_word_t is too small");

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

                "crypto_word_t is too small");

  static_assert(BN_BITS2 == sizeof(BN_ULONG) * 8, "BN_ULONG has padding bits");

  // C has very bizarre rules for types smaller than an int.

  static_assert(sizeof(BN_ULONG) >= sizeof(int),

                "BN_ULONG gets promoted to int");

  crypto_word_t mask;

  int bits = 0;

#if BN_BITS2 > 32

  // Check if the lower half of |x| are all zero.

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 32));

  // If the lower half is all zeros, it is included in the bit count and we

  // count the upper half. Otherwise, we count the lower half.

  bits += 32 & mask;

  l = constant_time_select_w(mask, l >> 32, l);

#endif

  // The remaining blocks are analogous iterations at lower powers of two.

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 16));

  bits += 16 & mask;

  l = constant_time_select_w(mask, l >> 16, l);

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 8));

  bits += 8 & mask;

  l = constant_time_select_w(mask, l >> 8, l);

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 4));

  bits += 4 & mask;

  l = constant_time_select_w(mask, l >> 4, l);

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 2));

  bits += 2 & mask;

  l = constant_time_select_w(mask, l >> 2, l);

  mask = constant_time_is_zero_w(l << (BN_BITS2 - 1));

  bits += 1 & mask;

  return bits;

}

int BN_count_low_zero_bits(const BIGNUM *bn) {

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

                "crypto_word_t is too small");

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

                "crypto_word_t is too small");

  int ret = 0;

  crypto_word_t saw_nonzero = 0;

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

    crypto_word_t nonzero = ~constant_time_is_zero_w(bn->d[i]);

    crypto_word_t first_nonzero = ~saw_nonzero & nonzero;

    saw_nonzero |= nonzero;

    int bits = bn_count_low_zero_bits_word(bn->d[i]);

    ret |= first_nonzero & (i * BN_BITS2 + bits);

  }

  // If got to the end of |bn| and saw no non-zero words, |bn| is zero. |ret|

  // will then remain zero.

  return ret;

}