fix: fix decompose_generators_fold (PROOF-620) (#16)

* work around

* reference bug

* fix bug

sxt/proof/inner_product/generator_fold.cc

@@ -33,14 +33,15 @@ void decompose_generator_fold(basct::span<unsigned>& res, const s25t::element& m
                               const s25t::element& m_high) noexcept {
   SXT_DEBUG_ASSERT(res.size() == s25cn::max_bits_v);
   size_t bit_index = 0;
+
   for (size_t i = 0; i < 4; ++i) {
     uint64_t x, y;
     std::memcpy(&x, reinterpret_cast<const char*>(&m_low) + sizeof(uint64_t) * i, sizeof(uint64_t));
     std::memcpy(&y, reinterpret_cast<const char*>(&m_high) + sizeof(uint64_t) * i,
                 sizeof(uint64_t));
     auto m = std::min(s25cn::max_bits_v - bit_index, 64ul);
     for (size_t bit_offset = 0; bit_offset < m; ++bit_offset) {
-      auto mask = 1ull << bit_index;
+      auto mask = 1ull << (bit_index - i * 64);
       res[bit_index++] =
           static_cast<unsigned>((x & mask) != 0) + 2u * static_cast<unsigned>((y & mask) != 0);
     }
@@ -58,9 +59,9 @@ void decompose_generator_fold(basct::span<unsigned>& res, const s25t::element& m
 //--------------------------------------------------------------------------------------------------
 // fold_generators
 //--------------------------------------------------------------------------------------------------
-CUDA_CALLABLE void fold_generators(c21t::element_p3& res, basct::cspan<unsigned> decomposition,
-                                   const c21t::element_p3& g_low,
-                                   const c21t::element_p3& g_high) noexcept {
+CUDA_CALLABLE
+void fold_generators(c21t::element_p3& res, basct::cspan<unsigned> decomposition,
+                     const c21t::element_p3& g_low, const c21t::element_p3& g_high) noexcept {
   if (decomposition.empty()) {
     // this should never happen
     res = c21t::element_p3::identity();