int aws_mp_karatsuba_sqr()

in AWSCognitoIdentityProvider/Internal/JKBigInteger/LibTomMath/tommath.c [977:1074]

• 71 lines of code
• 19 McCabe index (conditional complexity)

int aws_mp_karatsuba_sqr(aws_mp_int *a, aws_mp_int *b)
{
  aws_mp_int x0, x1, t1, t2, x0x0, x1x1;
  int     B, err;

  err = AWS_MP_MEM;

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

  /* now divide in two */
  B = B >> 1;

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

  /* init temps */
  if (aws_mp_init_size(&t1, a->used * 2) != AWS_MP_OKAY)
    goto X1;
  if (aws_mp_init_size(&t2, a->used * 2) != AWS_MP_OKAY)
    goto T1;
  if (aws_mp_init_size(&x0x0, B * 2) != AWS_MP_OKAY)
    goto T2;
  if (aws_mp_init_size(&x1x1, (a->used - B) * 2) != AWS_MP_OKAY)
    goto X0X0;

  {
    register int x;
    register aws_mp_digit *dst, *src;

    src = a->dp;

    /* now shift the digits */
    dst = x0.dp;
    for (x = 0; x < B; x++) {
      *dst++ = *src++;
    }

    dst = x1.dp;
    for (x = B; x < a->used; x++) {
      *dst++ = *src++;
    }
  }

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

    aws_mp_clamp(&x0);

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

  /* now calc (x1+x0)**2 */
  if (aws_s_mp_add(&x1, &x0, &t1) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = x1 - x0 */
  if (aws_mp_sqr(&t1, &t1) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = (x1 - x0) * (x1 - x0) */

  /* add x0y0 */
  if (aws_s_mp_add(&x0x0, &x1x1, &t2) != AWS_MP_OKAY)
    goto X1X1;           /* t2 = x0x0 + x1x1 */
  if (aws_s_mp_sub(&t1, &t2, &t1) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */

  /* shift by B */
  if (aws_mp_lshd(&t1, B) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
  if (aws_mp_lshd(&x1x1, B * 2) != AWS_MP_OKAY)
    goto X1X1;           /* x1x1 = x1x1 << 2*B */

  if (aws_mp_add(&x0x0, &t1, &t1) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = x0x0 + t1 */
  if (aws_mp_add(&t1, &x1x1, b) != AWS_MP_OKAY)
    goto X1X1;           /* t1 = x0x0 + t1 + x1x1 */

  err = AWS_MP_OKAY;

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