From 459f4a5e7aecd0a069d4ea4d6ea92a5611a17502 Mon Sep 17 00:00:00 2001
From: Pavol Rusnak <stick@gk2.sk>
Date: Mon, 31 Oct 2016 17:26:24 +0100
Subject: [PATCH] add setbit, clearbit, testbit and xor to bignum

---
 bignum.c | 27 +++++++++++++++++++++++++++
 bignum.h |  8 ++++++++
 2 files changed, 35 insertions(+)

diff --git a/bignum.c b/bignum.c
index eed53d22be..b2a20f9747 100644
--- a/bignum.c
+++ b/bignum.c
@@ -296,6 +296,33 @@ void bn_rshift(bignum256 *a)
 	a->val[8] >>= 1;
 }
 
+// sets bit in bignum
+void bn_setbit(bignum256 *a, uint8_t bit)
+{
+	a->val[bit / 30] |= (1 << (bit % 30));
+}
+
+// clears bit in bignum
+void bn_clearbit(bignum256 *a, uint8_t bit)
+{
+	a->val[bit / 30] &= ~(1 << (bit % 30));
+}
+
+// tests bit in bignum
+uint32_t bn_testbit(bignum256 *a, uint8_t bit)
+{
+	return a->val[bit / 30] & (1 << (bit % 30));
+}
+
+// a = b ^ c
+void bn_xor(bignum256 *a, const bignum256 *b, const bignum256 *c)
+{
+	int i;
+	for (i = 0; i < 9; i++) {
+		a->val[i] = b->val[i] ^ c->val[i];
+	}
+}
+
 // multiply x by 1/2 modulo prime.
 // it computes x = (x & 1) ? (x + prime) >> 1 : x >> 1.
 // assumes x is normalized.
diff --git a/bignum.h b/bignum.h
index 451e344891..83ae314ce9 100644
--- a/bignum.h
+++ b/bignum.h
@@ -105,6 +105,14 @@ void bn_lshift(bignum256 *a);
 
 void bn_rshift(bignum256 *a);
 
+void bn_setbit(bignum256 *a, uint8_t bit);
+
+void bn_clearbit(bignum256 *a, uint8_t bit);
+
+uint32_t bn_testbit(bignum256 *a, uint8_t bit);
+
+void bn_xor(bignum256 *a, const bignum256 *b, const bignum256 *c);
+
 void bn_mult_half(bignum256 *x, const bignum256 *prime);
 
 void bn_mult_k(bignum256 *x, uint8_t k, const bignum256 *prime);