bignum: introduce is_even/is_odd

bignum.h

@@ -1,6 +1,7 @@
 /**
  * Copyright (c) 2013-2014 Tomas Dzetkulic
  * Copyright (c) 2013-2014 Pavol Rusnak
+ * Copyright (c) 2016 Alex Beregszaszi
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the "Software"),
@@ -59,6 +60,14 @@ void bn_zero(bignum256 *a);
 
 int bn_is_zero(const bignum256 *a);
 
+static inline int bn_is_even(const bignum256 *a) {
+	return (a->val[0] & 1) == 0;
+}
+
+static inline int bn_is_odd(const bignum256 *a) {
+	return (a->val[0] & 1) == 1;
+}
+
 int bn_is_less(const bignum256 *a, const bignum256 *b);
 
 int bn_is_equal(const bignum256 *a, const bignum256 *b);

tests.c

@@ -165,6 +165,36 @@ START_TEST(test_bignum_copy)
 }
 END_TEST
 
+START_TEST(test_bignum_is_even)
+{
+	bignum256 a;
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd5"), &a);
+	ck_assert_int_eq(bn_is_even(&a), 0);
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd2"), &a);
+	ck_assert_int_eq(bn_is_even(&a), 1);
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd0"), &a);
+	ck_assert_int_eq(bn_is_even(&a), 1);
+}
+END_TEST
+
+START_TEST(test_bignum_is_odd)
+{
+	bignum256 a;
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd5"), &a);
+	ck_assert_int_eq(bn_is_odd(&a), 1);
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd2"), &a);
+	ck_assert_int_eq(bn_is_odd(&a), 0);
+
+	bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd0"), &a);
+	ck_assert_int_eq(bn_is_odd(&a), 0);
+}
+END_TEST
+
 // from https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json
 START_TEST(test_base58)
 {
@@ -2416,6 +2446,8 @@ Suite *test_suite(void)
 	tcase_add_test(tc, test_bignum_read_le);
 	tcase_add_test(tc, test_bignum_write_le);
 	tcase_add_test(tc, test_bignum_copy);
+	tcase_add_test(tc, test_bignum_is_even);
+	tcase_add_test(tc, test_bignum_is_odd);
 	suite_add_tcase(s, tc);
 
 	tc = tcase_create("base58");