text: /*
   * Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.
   *
   * Licensed under the OpenSSL license (the "License").  You may not use
   * this file except in compliance with the License.  You can obtain a copy
   * in the file LICENSE in the source distribution or at
   * https://www.openssl.org/source/license.html
   */
  
  #include <openssl/crypto.h>
  #include "modes_lcl.h"
  #include <string.h>
  
  /*
   * NOTE: the IV/counter CTR mode is big-endian.  The code itself is
   * endian-neutral.
   */
  
  /* increment counter (128-bit int) by 1 */
  static void ctr128_inc(unsigned char *counter)
  {
      u32 n = 16, c = 1;
  
      do {
          --n;
          c += counter[n];
          counter[n] = (u8)c;
          c >>= 8;
      } while (n);
  }
  
  #if !defined(OPENSSL_SMALL_FOOTPRINT)
  static void ctr128_inc_aligned(unsigned char *counter)
  {
      size_t *data, c, d, n;
      const union {
          long one;
          char little;
      } is_endian = {
          1
      };
  
      if (is_endian.little || ((size_t)counter % sizeof(size_t)) != 0) {
          ctr128_inc(counter);
          return;
      }
  
      data = (size_t *)counter;
      c = 1;
      n = 16 / sizeof(size_t);
      do {
          --n;
          d = data[n] += c;
          /* did addition carry? */
          c = ((d - c) ^ d) >> (sizeof(size_t) * 8 - 1);
      } while (n);
  }
  #endif
  
  /*
   * The input encrypted as though 128bit counter mode is being used.  The
   * extra state information to record how much of the 128bit block we have
   * used is contained in *num, and the encrypted counter is kept in
   * ecount_buf.  Both *num and ecount_buf must be initialised with zeros
   * before the first call to CRYPTO_ctr128_encrypt(). This algorithm assumes
   * that the counter is in the x lower bits of the IV (ivec), and that the
   * application has full control over overflow and the rest of the IV.  This
   * implementation takes NO responsibility for checking that the counter
   * doesn't overflow into the rest of the IV when incremented.
   */
  void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,
                             size_t len, const void *key,
                             unsigned char ivec[16],
                             unsigned char ecount_buf[16], unsigned int *num,
                             block128_f block)
  {
      unsigned int n;
      size_t l = 0;
  
      n = *num;
  
  #if !defined(OPENSSL_SMALL_FOOTPRINT)
      if (16 % sizeof(size_t) == 0) { /* always true actually */
          do {
              while (n && len) {
                  *(out++) = *(in++) ^ ecount_buf[n];
                  --len;
                  n = (n + 1) % 16;
              }
  
  # if defined(STRICT_ALIGNMENT)
              if (((size_t)in | (size_t)out | (size_t)ecount_buf)
                  % sizeof(size_t) != 0)
                  break;
  # endif
              while (len >= 16) {
                  (*block) (ivec, ecount_buf, key);
                  ctr128_inc_aligned(ivec);
                  for (n = 0; n < 16; n += sizeof(size_t))
                      *(size_t *)(out + n) =
                          *(size_t *)(in + n) ^ *(size_t *)(ecount_buf + n);
                  len -= 16;
                  out += 16;
                  in += 16;
                  n = 0;
              }
              if (len) {
                  (*block) (ivec, ecount_buf, key);
                  ctr128_inc_aligned(ivec);
                  while (len--) {
                      out[n] = in[n] ^ ecount_buf[n];
                      ++n;
                  }
              }
              *num = n;
              return;
          } while (0);
      }
      /* the rest would be commonly eliminated by x86* compiler */
  #endif
      while (l < len) {
          if (n == 0) {
              (*block) (ivec, ecount_buf, key);
              ctr128_inc(ivec);
          }
          out[l] = in[l] ^ ecount_buf[n];
          ++l;
          n = (n + 1) % 16;
      }
  
      *num = n;
  }
  
  /* increment upper 96 bits of 128-bit counter by 1 */
  static void ctr96_inc(unsigned char *counter)
  {
      u32 n = 12, c = 1;
  
      do {
          --n;
          c += counter[n];
          counter[n] = (u8)c;
          c >>= 8;
      } while (n);
  }
  
  void CRYPTO_ctr128_encrypt_ctr32(const unsigned char *in, unsigned char *out,
                                   size_t len, const void *key,
                                   unsigned char ivec[16],
                                   unsigned char ecount_buf[16],
                                   unsigned int *num, ctr128_f func)
  {
      unsigned int n, ctr32;
  
      n = *num;
  
      while (n && len) {
          *(out++) = *(in++) ^ ecount_buf[n];
          --len;
          n = (n + 1) % 16;
      }
  
      ctr32 = GETU32(ivec + 12);
      while (len >= 16) {
          size_t blocks = len / 16;
          /*
           * 1<<28 is just a not-so-small yet not-so-large number...
           * Below condition is practically never met, but it has to
           * be checked for code correctness.
           */
          if (sizeof(size_t) > sizeof(unsigned int) && blocks > (1U << 28))
              blocks = (1U << 28);
          /*
           * As (*func) operates on 32-bit counter, caller
           * has to handle overflow. 'if' below detects the
           * overflow, which is then handled by limiting the
           * amount of blocks to the exact overflow point...
           */
          ctr32 += (u32)blocks;
          if (ctr32 < blocks) {
              blocks -= ctr32;
              ctr32 = 0;
          }
          (*func) (in, out, blocks, key, ivec);
          /* (*ctr) does not update ivec, caller does: */
          PUTU32(ivec + 12, ctr32);
          /* ... overflow was detected, propagate carry. */
          if (ctr32 == 0)
              ctr96_inc(ivec);
          blocks *= 16;
          len -= blocks;
          out += blocks;
          in += blocks;
      }
      if (len) {
          memset(ecount_buf, 0, 16);
          (*func) (ecount_buf, ecount_buf, 1, key, ivec);
          ++ctr32;
          PUTU32(ivec + 12, ctr32);
          if (ctr32 == 0)
              ctr96_inc(ivec);
          while (len--) {
              out[n] = in[n] ^ ecount_buf[n];
              ++n;
          }
      }
  
      *num = n;
  }
  