From ed3377db8416935dc4ad8263da5f9b3d12c5c26b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Thu, 17 Jul 2014 22:28:47 +0200
Subject: [PATCH] Reduce ecc_add_eh scratch need.
---
ChangeLog | 3 +++
ecc-add-eh.c | 62 ++++++++++++++++++++++++++------------------------
ecc-internal.h | 2 +-
3 files changed, 36 insertions(+), 31 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 0de42229..0f159f44 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
2014-07-17 Niels Möller <nisse@lysator.liu.se>
+ * ecc-add-eh.c (ecc_add_eh): Reduce scratch need.
+ * ecc-internal.h (ECC_ADD_EH_ITCH): Reduced to 6*size.
+
* testsuite/curve25519-dup-test.c (test_main): Free allocated
storage.
diff --git a/ecc-add-eh.c b/ecc-add-eh.c
index 05c2188e..a3471b26 100644
--- a/ecc-add-eh.c
+++ b/ecc-add-eh.c
@@ -65,47 +65,49 @@ ecc_add_eh (const struct ecc_curve *ecc,
Computation Operation Live variables
- B = z1^2 sqr B
- C = x1*x2 mul B, C
- D = y1*y2 mul B, C, D
- E = b*C*D 2 mul B, C, D, E
- F = B - E B, C, D, E, F
- G = B + E C, D, F, G
- x3 = z1*F*[(x1+y1)(x2+y2) - C - D] 3 mul C, D, G
+ C = x1*x2 mul C
+ D = y1*y2 mul C, D
+ T = (x1+y1)(x2+y2) - C - D C, D, T
+ E = b*C*D 2 mul C, E, T (Replace C <-- D - C)
+ B = z1^2 sqr B, C, E, T
+ F = B - E B, C, E, F, T
+ G = B + E C, F, G, T
+ x3 = z1*F*T 3 mul C, F, G, T
y3 = z1*G*(D-C) 2 mul F, G
z3 = F*G mul
*/
-#define B (scratch)
-#define C (scratch + 1*ecc->size)
-#define D (scratch + 2*ecc->size)
+#define C (scratch)
+#define D (scratch + 1*ecc->size)
+#define T (scratch + 2*ecc->size)
#define E (scratch + 3*ecc->size)
-#define F (scratch + 4*ecc->size)
-#define G (scratch + 5*ecc->size)
-#define T (scratch + 6*ecc->size)
-
- ecc_modp_sqr (ecc, B, z1);
+#define B (scratch + 4*ecc->size)
+#define F D
+#define G E
+
ecc_modp_mul (ecc, C, x1, x2);
ecc_modp_mul (ecc, D, y1, y2);
- ecc_modp_mul (ecc, T, C, D);
- ecc_modp_mul (ecc, E, T, ecc->b);
+ ecc_modp_add (ecc, x3, x1, y1);
+ ecc_modp_add (ecc, y3, x2, y2);
+ ecc_modp_mul (ecc, T, x3, y3);
+ ecc_modp_sub (ecc, T, T, C);
+ ecc_modp_sub (ecc, T, T, D);
+ ecc_modp_mul (ecc, x3, C, D);
+ ecc_modp_mul (ecc, E, x3, ecc->b);
+
+ ecc_modp_sub (ecc, C, D, C);
+ ecc_modp_sqr (ecc, B, z1);
ecc_modp_sub (ecc, F, B, E);
- ecc_modp_add (ecc, G, B, E);
+ ecc_modp_add (ecc, G, B, E);
/* x3 */
- ecc_modp_add (ecc, B, x1, y1);
- ecc_modp_add (ecc, E, x2, y2);
- ecc_modp_mul (ecc, T, B, E);
- ecc_modp_sub (ecc, T, T, C);
- ecc_modp_sub (ecc, x3, T, D);
- ecc_modp_mul (ecc, T, x3, z1);
- ecc_modp_mul (ecc, x3, T, F);
+ ecc_modp_mul (ecc, B, F, T);
+ ecc_modp_mul (ecc, x3, B, z1);
/* y3 */
- ecc_modp_sub (ecc, C, D, C);
- ecc_modp_mul (ecc, T, z1, C);
- ecc_modp_mul (ecc, y3, T, G);
+ ecc_modp_mul (ecc, B, G, C);
+ ecc_modp_mul (ecc, y3, B, z1);
/* z3 */
- ecc_modp_mul (ecc, T, F, G);
- mpn_copyi (z3, T, ecc->size);
+ ecc_modp_mul (ecc, B, F, G);
+ mpn_copyi (z3, B, ecc->size);
}
diff --git a/ecc-internal.h b/ecc-internal.h
index f2b99278..78d05302 100644
--- a/ecc-internal.h
+++ b/ecc-internal.h
@@ -242,7 +242,7 @@ sec_modinv (mp_limb_t *vp, mp_limb_t *ap, mp_size_t n,
#define ECC_DUP_EH_ITCH(size) (5*(size))
#define ECC_ADD_JJA_ITCH(size) (6*(size))
#define ECC_ADD_JJJ_ITCH(size) (8*(size))
-#define ECC_ADD_EH_ITCH(size) (8*(size))
+#define ECC_ADD_EH_ITCH(size) (6*(size))
#define ECC_ADD_EHH_ITCH(size) (9*(size))
#define ECC_MUL_G_ITCH(size) (9*(size))
#if ECC_MUL_A_WBITS == 0
--
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