text: /* crypto/bn/bn_sqr.c */
  /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   * All rights reserved.
   *
   * This package is an SSL implementation written
   * by Eric Young (eay@cryptsoft.com).
   * The implementation was written so as to conform with Netscapes SSL.
   *
   * This library is free for commercial and non-commercial use as long as
   * the following conditions are aheared to.  The following conditions
   * apply to all code found in this distribution, be it the RC4, RSA,
   * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
   * included with this distribution is covered by the same copyright terms
   * except that the holder is Tim Hudson (tjh@cryptsoft.com).
   *
   * Copyright remains Eric Young's, and as such any Copyright notices in
   * the code are not to be removed.
   * If this package is used in a product, Eric Young should be given attribution
   * as the author of the parts of the library used.
   * This can be in the form of a textual message at program startup or
   * in documentation (online or textual) provided with the package.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *    "This product includes cryptographic software written by
   *     Eric Young (eay@cryptsoft.com)"
   *    The word 'cryptographic' can be left out if the rouines from the library
   *    being used are not cryptographic related :-).
   * 4. If you include any Windows specific code (or a derivative thereof) from
   *    the apps directory (application code) you must include an acknowledgement:
   *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
   *
   * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * The licence and distribution terms for any publically available version or
   * derivative of this code cannot be changed.  i.e. this code cannot simply be
   * copied and put under another distribution licence
   * [including the GNU Public Licence.]
   */
  
  #include <stdio.h>
  #include "cryptlib.h"
  #include "bn_lcl.h"
  
  /* r must not be a */
  /*
   * I've just gone over this and it is now %20 faster on x86 - eay - 27 Jun 96
   */
  int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
  {
      int ret = bn_sqr_fixed_top(r, a, ctx);
  
      bn_correct_top(r);
      bn_check_top(r);
  
      return ret;
  }
  
  int bn_sqr_fixed_top(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
  {
      int max, al;
      int ret = 0;
      BIGNUM *tmp, *rr;
  
  #ifdef BN_COUNT
      fprintf(stderr, "BN_sqr %d * %d\n", a->top, a->top);
  #endif
      bn_check_top(a);
  
      al = a->top;
      if (al <= 0) {
          r->top = 0;
          r->neg = 0;
          return 1;
      }
  
      BN_CTX_start(ctx);
      rr = (a != r) ? r : BN_CTX_get(ctx);
      tmp = BN_CTX_get(ctx);
      if (!rr || !tmp)
          goto err;
  
      max = 2 * al;               /* Non-zero (from above) */
      if (bn_wexpand(rr, max) == NULL)
          goto err;
  
      if (al == 4) {
  #ifndef BN_SQR_COMBA
          BN_ULONG t[8];
          bn_sqr_normal(rr->d, a->d, 4, t);
  #else
          bn_sqr_comba4(rr->d, a->d);
  #endif
      } else if (al == 8) {
  #ifndef BN_SQR_COMBA
          BN_ULONG t[16];
          bn_sqr_normal(rr->d, a->d, 8, t);
  #else
          bn_sqr_comba8(rr->d, a->d);
  #endif
      } else {
  #if defined(BN_RECURSION)
          if (al < BN_SQR_RECURSIVE_SIZE_NORMAL) {
              BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL * 2];
              bn_sqr_normal(rr->d, a->d, al, t);
          } else {
              int j, k;
  
              j = BN_num_bits_word((BN_ULONG)al);
              j = 1 << (j - 1);
              k = j + j;
              if (al == j) {
                  if (bn_wexpand(tmp, k * 2) == NULL)
                      goto err;
                  bn_sqr_recursive(rr->d, a->d, al, tmp->d);
              } else {
                  if (bn_wexpand(tmp, max) == NULL)
                      goto err;
                  bn_sqr_normal(rr->d, a->d, al, tmp->d);
              }
          }
  #else
          if (bn_wexpand(tmp, max) == NULL)
              goto err;
          bn_sqr_normal(rr->d, a->d, al, tmp->d);
  #endif
      }
  
      rr->neg = 0;
      rr->top = max;
      rr->flags |= BN_FLG_FIXED_TOP;
      if (r != rr && BN_copy(r, rr) == NULL)
          goto err;
  
      ret = 1;
   err:
      bn_check_top(rr);
      bn_check_top(tmp);
      BN_CTX_end(ctx);
      return (ret);
  }
  
  /* tmp must have 2*n words */
  void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp)
  {
      int i, j, max;
      const BN_ULONG *ap;
      BN_ULONG *rp;
  
      max = n * 2;
      ap = a;
      rp = r;
      rp[0] = rp[max - 1] = 0;
      rp++;
      j = n;
  
      if (--j > 0) {
          ap++;
          rp[j] = bn_mul_words(rp, ap, j, ap[-1]);
          rp += 2;
      }
  
      for (i = n - 2; i > 0; i--) {
          j--;
          ap++;
          rp[j] = bn_mul_add_words(rp, ap, j, ap[-1]);
          rp += 2;
      }
  
      bn_add_words(r, r, r, max);
  
      /* There will not be a carry */
  
      bn_sqr_words(tmp, a, n);
  
      bn_add_words(r, r, tmp, max);
  }
  
  #ifdef BN_RECURSION
  /*-
   * r is 2*n words in size,
   * a and b are both n words in size.    (There's not actually a 'b' here ...)
   * n must be a power of 2.
   * We multiply and return the result.
   * t must be 2*n words in size
   * We calculate
   * a[0]*b[0]
   * a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])
   * a[1]*b[1]
   */
  void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)
  {
      int n = n2 / 2;
      int zero, c1;
      BN_ULONG ln, lo, *p;
  
  # ifdef BN_COUNT
      fprintf(stderr, " bn_sqr_recursive %d * %d\n", n2, n2);
  # endif
      if (n2 == 4) {
  # ifndef BN_SQR_COMBA
          bn_sqr_normal(r, a, 4, t);
  # else
          bn_sqr_comba4(r, a);
  # endif
          return;
      } else if (n2 == 8) {
  # ifndef BN_SQR_COMBA
          bn_sqr_normal(r, a, 8, t);
  # else
          bn_sqr_comba8(r, a);
  # endif
          return;
      }
      if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL) {
          bn_sqr_normal(r, a, n2, t);
          return;
      }
      /* r=(a[0]-a[1])*(a[1]-a[0]) */
      c1 = bn_cmp_words(a, &(a[n]), n);
      zero = 0;
      if (c1 > 0)
          bn_sub_words(t, a, &(a[n]), n);
      else if (c1 < 0)
          bn_sub_words(t, &(a[n]), a, n);
      else
          zero = 1;
  
      /* The result will always be negative unless it is zero */
      p = &(t[n2 * 2]);
  
      if (!zero)
          bn_sqr_recursive(&(t[n2]), t, n, p);
      else
          memset(&(t[n2]), 0, n2 * sizeof(BN_ULONG));
      bn_sqr_recursive(r, a, n, p);
      bn_sqr_recursive(&(r[n2]), &(a[n]), n, p);
  
      /*-
       * t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero
       * r[10] holds (a[0]*b[0])
       * r[32] holds (b[1]*b[1])
       */
  
      c1 = (int)(bn_add_words(t, r, &(r[n2]), n2));
  
      /* t[32] is negative */
      c1 -= (int)(bn_sub_words(&(t[n2]), t, &(t[n2]), n2));
  
      /*-
       * t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])
       * r[10] holds (a[0]*a[0])
       * r[32] holds (a[1]*a[1])
       * c1 holds the carry bits
       */
      c1 += (int)(bn_add_words(&(r[n]), &(r[n]), &(t[n2]), n2));
      if (c1) {
          p = &(r[n + n2]);
          lo = *p;
          ln = (lo + c1) & BN_MASK2;
          *p = ln;
  
          /*
           * The overflow will stop before we over write words we should not
           * overwrite
           */
          if (ln < (BN_ULONG)c1) {
              do {
                  p++;
                  lo = *p;
                  ln = (lo + 1) & BN_MASK2;
                  *p = ln;
              } while (ln == 0);
          }
      }
  }
  #endif
  