/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is library that provides for multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library is designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tomstdenis@iahu.ca, http://libtommath.iahu.ca
 */
#include <tommath.h>

/* Karatsuba squaring, computes b = a*a using three half size squarings
 *
 * See comments of mp_karatsuba_mul for details.  It is essentially the same algorithm
 * but merely tuned to perform recursive squarings.
 */
int
mp_karatsuba_sqr (mp_int * a, mp_int * b)
{
  mp_int  x0, x1, t1, t2, x0x0, x1x1;
  int     B, err, x;


  err = MP_MEM;

  /* min # of digits */
  B = a->used;

  /* now divide in two */
  B = B / 2;

  /* init copy all the temps */
  if (mp_init_size (&x0, B) != MP_OKAY)
    goto ERR;
  if (mp_init_size (&x1, a->used - B) != MP_OKAY)
    goto X0;

  /* init temps */
  if (mp_init (&t1) != MP_OKAY)
    goto X1;
  if (mp_init (&t2) != MP_OKAY)
    goto T1;
  if (mp_init (&x0x0) != MP_OKAY)
    goto T2;
  if (mp_init (&x1x1) != MP_OKAY)
    goto X0X0;

  /* now shift the digits */
  for (x = 0; x < B; x++) {
    x0.dp[x] = a->dp[x];
  }

  for (x = B; x < a->used; x++) {
    x1.dp[x - B] = a->dp[x];
  }

  x0.used = B;
  x1.used = a->used - B;

  mp_clamp (&x0);

  /* now calc the products x0*x0 and x1*x1 */
  if (mp_sqr (&x0, &x0x0) != MP_OKAY)
    goto X1X1;			/* x0x0 = x0*x0 */
  if (mp_sqr (&x1, &x1x1) != MP_OKAY)
    goto X1X1;			/* x1x1 = x1*x1 */

  /* now calc x1-x0 and y1-y0 */
  if (mp_sub (&x1, &x0, &t1) != MP_OKAY)
    goto X1X1;			/* t1 = x1 - x0 */
  if (mp_sqr (&t1, &t1) != MP_OKAY)
    goto X1X1;			/* t1 = (x1 - x0) * (y1 - y0) */

  /* add x0y0 */
  if (mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
    goto X1X1;			/* t2 = x0y0 + x1y1 */
  if (mp_sub (&t2, &t1, &t1) != MP_OKAY)
    goto X1X1;			/* t1 = x0y0 + x1y1 - (x1-x0)*(y1-y0) */

  /* shift by B */
  if (mp_lshd (&t1, B) != MP_OKAY)
    goto X1X1;			/* t1 = (x0y0 + x1y1 - (x1-x0)*(y1-y0))<<B */
  if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
    goto X1X1;			/* x1y1 = x1y1 << 2*B */

  if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
    goto X1X1;			/* t1 = x0y0 + t1 */
  if (mp_add (&t1, &x1x1, b) != MP_OKAY)
    goto X1X1;			/* t1 = x0y0 + t1 + x1y1 */

  err = MP_OKAY;

X1X1:mp_clear (&x1x1);
X0X0:mp_clear (&x0x0);
T2:mp_clear (&t2);
T1:mp_clear (&t1);
X1:mp_clear (&x1);
X0:mp_clear (&x0);
ERR:
  return err;
}