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-rw-r--r--libtommath/bn_mp_karatsuba_sqr.c117
1 files changed, 117 insertions, 0 deletions
diff --git a/libtommath/bn_mp_karatsuba_sqr.c b/libtommath/bn_mp_karatsuba_sqr.c
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+++ b/libtommath/bn_mp_karatsuba_sqr.c
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+#include <tommath.h>
+#ifdef BN_MP_KARATSUBA_SQR_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was 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://math.libtomcrypt.org
+ */
+
+/* Karatsuba squaring, computes b = a*a using three
+ * half size squarings
+ *
+ * See comments of 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;
+
+ err = MP_MEM;
+
+ /* min # of digits */
+ B = a->used;
+
+ /* now divide in two */
+ B = B >> 1;
+
+ /* 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_size (&t1, a->used * 2) != MP_OKAY)
+ goto X1;
+ if (mp_init_size (&t2, a->used * 2) != MP_OKAY)
+ goto T1;
+ if (mp_init_size (&x0x0, B * 2) != MP_OKAY)
+ goto T2;
+ if (mp_init_size (&x1x1, (a->used - B) * 2) != MP_OKAY)
+ goto X0X0;
+
+ {
+ register int x;
+ register 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;
+
+ 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)**2 */
+ 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) * (x1 - x0) */
+
+ /* add x0y0 */
+ if (s_mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
+ goto X1X1; /* t2 = x0x0 + x1x1 */
+ if (mp_sub (&t2, &t1, &t1) != MP_OKAY)
+ goto X1X1; /* t1 = x0x0 + x1x1 - (x1-x0)*(x1-x0) */
+
+ /* shift by B */
+ if (mp_lshd (&t1, B) != MP_OKAY)
+ goto X1X1; /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
+ if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
+ goto X1X1; /* x1x1 = x1x1 << 2*B */
+
+ if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
+ goto X1X1; /* t1 = x0x0 + t1 */
+ if (mp_add (&t1, &x1x1, b) != MP_OKAY)
+ goto X1X1; /* t1 = x0x0 + t1 + x1x1 */
+
+ 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;
+}
+#endif