From 2e8ae88394c3917c539937fad5b192b0397dc730 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Fri, 1 Jan 2021 18:14:29 +0200
Subject: [PATCH] Remove dependence on multiprecision::lsb, msb

---
 .../boost/random/detail/gray_coded_qrng.hpp   | 29 +++++++++++++++++--
 include/boost/random/niederreiter_base2.hpp   |  2 +-
 include/boost/random/sobol.hpp                |  3 +-
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/include/boost/random/detail/gray_coded_qrng.hpp b/include/boost/random/detail/gray_coded_qrng.hpp
index 7589c5f..f527487 100644
--- a/include/boost/random/detail/gray_coded_qrng.hpp
+++ b/include/boost/random/detail/gray_coded_qrng.hpp
@@ -11,7 +11,9 @@
 
 #include <boost/random/detail/qrng_base.hpp>
 
-#include <boost/multiprecision/integer.hpp> // lsb
+#include <boost/core/bit.hpp> // lsb
+#include <boost/throw_exception.hpp>
+#include <stdexcept>
 
 #include <functional> // bit_xor
 
@@ -27,6 +29,26 @@ namespace random {
 
 namespace qrng_detail {
 
+template<class T> static int lsb( T x )
+{
+  if( x == 0 )
+  {
+    BOOST_THROW_EXCEPTION( std::range_error( "qrng_detail::lsb: argument is 0" ) );
+  }
+
+  return boost::core::countr_zero( x );
+}
+
+template<class T> static int msb( T x )
+{
+  if( x == 0 )
+  {
+    BOOST_THROW_EXCEPTION( std::range_error( "qrng_detail::msb: argument is 0" ) );
+  }
+
+  return std::numeric_limits<T>::digits - 1 - boost::core::countl_zero( x );
+}
+
 template<typename LatticeT>
 class gray_coded_qrng
   : public qrng_base<
@@ -111,7 +133,7 @@ public:
       // We don't want negative seeds.
       check_seed_sign(init);
 
-      size_type seq_code = boost::next(init);
+      size_type seq_code = init + 1;
       if (BOOST_UNLIKELY(!(init < seq_code)))
         boost::throw_exception( std::range_error("gray_coded_qrng: seed") );
 
@@ -132,6 +154,7 @@ public:
   }
 
 private:
+
   void compute_seq(size_type seq)
   {
     // Find the position of the least-significant zero in sequence count.
@@ -139,7 +162,7 @@ private:
     // the count is advanced.
     // Xor'ing with max() has the effect of flipping all the bits in seq,
     // except for the sign bit.
-    unsigned r = multiprecision::lsb(seq ^ (self_t::max)());
+    unsigned r = qrng_detail::lsb(seq ^ (self_t::max)());
     check_bit_range_t::bit_pos(r);
     update_quasi(r);
   }
diff --git a/include/boost/random/niederreiter_base2.hpp b/include/boost/random/niederreiter_base2.hpp
index 149a4a4..e1a874b 100644
--- a/include/boost/random/niederreiter_base2.hpp
+++ b/include/boost/random/niederreiter_base2.hpp
@@ -123,7 +123,7 @@ public:
         boost::throw_exception( std::range_error("niederreiter_base2: polynomial value outside the given value type range") );
       }
 
-      const unsigned degree = multiprecision::msb(poly); // integer log2(poly)
+      const unsigned degree = qrng_detail::msb(poly); // integer log2(poly)
       const unsigned space_required = degree * ((bit_count / degree) + 1); // ~ degree + bit_count
 
       v.resize(degree + bit_count - 1);
diff --git a/include/boost/random/sobol.hpp b/include/boost/random/sobol.hpp
index 2518b37..703155b 100644
--- a/include/boost/random/sobol.hpp
+++ b/include/boost/random/sobol.hpp
@@ -11,6 +11,7 @@
 
 #include <boost/random/detail/sobol_table.hpp>
 #include <boost/random/detail/gray_coded_qrng.hpp>
+#include <boost/assert.hpp>
 
 namespace boost {
 namespace random {
@@ -61,7 +62,7 @@ public:
       if (poly > std::numeric_limits<value_type>::max()) {
         boost::throw_exception( std::range_error("sobol: polynomial value outside the given value type range") );
       }
-      const unsigned degree = multiprecision::msb(poly); // integer log2(poly)
+      const unsigned degree = qrng_detail::msb(poly); // integer log2(poly)
 
       // set initial values of m from table
       for (unsigned k = 0; k != degree; ++k)