Fix libsnark dependency build.

This changes libsnark to build in-place, instead of copying first to
a build directory. Previously, modifications made to the original
sources wouldn't get rebuilt without a 'make clean' because users
would be pointing to the copies.

This closes #2689.

src/snark/libsnark/algebra/fields/tests/test_bigint.cpp

@@ -0,0 +1,97 @@
+/**
+ *****************************************************************************
+ * @author     This file is part of libsnark, developed by SCIPR Lab
+ *             and contributors (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#include "algebra/fields/bigint.hpp"
+
+#include <gtest/gtest.h>
+
+using namespace libsnark;
+
+TEST(algebra, bigint)
+{
+    static_assert(ULONG_MAX == 0xFFFFFFFFFFFFFFFFul, "unsigned long not 64-bit");
+    static_assert(GMP_NUMB_BITS == 64, "GMP limb not 64-bit");
+
+    const char *b1_decimal = "76749407";
+    const char *b2_decimal = "435020359732196472065729437602";
+    const char *b3_decimal = "33387554642372758038536799358397002014";
+    const char *b2_binary = "0000000000000000000000000000010101111101101000000110100001011010"
+                            "1101101010001001000001101000101000100110011001110001111110100010";
+
+    bigint<1> b0 = bigint<1>(0ul);
+    bigint<1> b1 = bigint<1>(b1_decimal);
+    bigint<2> b2 = bigint<2>(b2_decimal);
+
+    EXPECT_EQ(b0.as_ulong(), 0ul);
+    EXPECT_TRUE(b0.is_zero());
+    EXPECT_EQ(b1.as_ulong(), 76749407ul);
+    EXPECT_FALSE(b1.is_zero());
+    EXPECT_EQ(b2.as_ulong(), 15747124762497195938ul);
+    EXPECT_FALSE(b2.is_zero());
+    EXPECT_NE(b0, b1);
+    EXPECT_FALSE(b0 == b1);
+
+    EXPECT_EQ(b2.max_bits(), 128);
+    EXPECT_EQ(b2.num_bits(), 99);
+    for (size_t i = 0; i < 128; i++) {
+        EXPECT_EQ(b2.test_bit(i), (b2_binary[127-i] == '1'));
+    }
+
+    bigint<3> b3 = b2 * b1;
+
+    EXPECT_EQ(b3, bigint<3>(b3_decimal));
+    EXPECT_FALSE(b3.is_zero());
+
+    bigint<3> b3a { b3 };
+    EXPECT_EQ(b3a, bigint<3>(b3_decimal));
+    EXPECT_EQ(b3a, b3);
+    EXPECT_FALSE(b3a.is_zero());
+
+    mpz_t m3;
+    mpz_init(m3);
+    b3.to_mpz(m3);
+    bigint<3> b3b { m3 };
+    EXPECT_EQ(b3b, b3);
+
+    bigint<2> quotient;
+    bigint<2> remainder;
+    bigint<3>::div_qr(quotient, remainder, b3, b2);
+    EXPECT_LT(quotient.num_bits(), GMP_NUMB_BITS);
+    EXPECT_EQ(quotient.as_ulong(), b1.as_ulong());
+    bigint<1> b1inc = bigint<1>("76749408");
+    bigint<1> b1a = quotient.shorten(b1inc, "test");
+    EXPECT_EQ(b1a, b1);
+    EXPECT_TRUE(remainder.is_zero());
+    remainder.limit(b2, "test");
+
+    EXPECT_THROW((void)(quotient.shorten(b1, "test")), std::domain_error);
+    EXPECT_THROW(remainder.limit(remainder, "test"), std::domain_error);
+
+    bigint<1> br = bigint<1>("42");
+    b3 += br;
+    EXPECT_NE(b3, b3a);
+    EXPECT_GT(b3, b3a);
+    EXPECT_FALSE(b3a > b3);
+
+    bigint<3>::div_qr(quotient, remainder, b3, b2);
+    EXPECT_LT(quotient.num_bits(), GMP_NUMB_BITS);
+    EXPECT_EQ(quotient.as_ulong(), b1.as_ulong());
+    EXPECT_LT(remainder.num_bits(), GMP_NUMB_BITS);
+    EXPECT_EQ(remainder.as_ulong(), 42);
+
+    b3a.clear();
+    EXPECT_TRUE(b3a.is_zero());
+    EXPECT_EQ(b3a.num_bits(), 0);
+    EXPECT_FALSE(b3.is_zero());
+
+    bigint<4> bx = bigint<4>().randomize();
+    bigint<4> by = bigint<4>().randomize();
+    EXPECT_FALSE(bx == by);
+
+    // TODO: test serialization
+}
+