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/common/utils.cpp

@@ -0,0 +1,102 @@
+/** @file
+ *****************************************************************************
+ Implementation of misc math and serialization utility functions
+ *****************************************************************************
+ * @author     This file is part of libsnark, developed by SCIPR Lab
+ *             and contributors (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstdarg>
+#include "common/utils.hpp"
+
+namespace libsnark {
+
+size_t log2(size_t n)
+/* returns ceil(log2(n)), so 1ul<<log2(n) is the smallest power of 2,
+   that is not less than n. */
+{
+    size_t r = ((n & (n-1)) == 0 ? 0 : 1); // add 1 if n is not power of 2
+
+    while (n > 1)
+    {
+        n >>= 1;
+        r++;
+    }
+
+    return r;
+}
+
+size_t bitreverse(size_t n, const size_t l)
+{
+    size_t r = 0;
+    for (size_t k = 0; k < l; ++k)
+    {
+        r = (r << 1) | (n & 1);
+        n >>= 1;
+    }
+    return r;
+}
+
+bit_vector int_list_to_bits(const std::initializer_list<unsigned long> &l, const size_t wordsize)
+{
+    bit_vector res(wordsize*l.size());
+    for (size_t i = 0; i < l.size(); ++i)
+    {
+        for (size_t j = 0; j < wordsize; ++j)
+        {
+            res[i*wordsize + j] = (*(l.begin()+i) & (1ul<<(wordsize-1-j)));
+        }
+    }
+    return res;
+}
+
+long long div_ceil(long long x, long long y)
+{
+    return (x + (y-1)) / y;
+}
+
+bool is_little_endian()
+{
+    uint64_t a = 0x12345678;
+    unsigned char *c = (unsigned char*)(&a);
+    return (*c = 0x78);
+}
+
+std::string FORMAT(const std::string &prefix, const char* format, ...)
+{
+    const static size_t MAX_FMT = 256;
+    char buf[MAX_FMT];
+    va_list args;
+    va_start(args, format);
+    vsnprintf(buf, MAX_FMT, format, args);
+    va_end(args);
+
+    return prefix + std::string(buf);
+}
+
+void serialize_bit_vector(std::ostream &out, const bit_vector &v)
+{
+    out << v.size() << "\n";
+    for (size_t i = 0; i < v.size(); ++i)
+    {
+        out << v[i] << "\n";
+    }
+}
+
+void deserialize_bit_vector(std::istream &in, bit_vector &v)
+{
+    size_t size;
+    in >> size;
+    v.resize(size);
+    for (size_t i = 0; i < size; ++i)
+    {
+        bool b;
+        in >> b;
+        v[i] = b;
+    }
+}
+} // libsnark