From b7da04c5941968cd21f02e2dd9dd5174a87b4f28 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 14 May 2023 03:39:39 +0300
Subject: [PATCH] Add an offset parameter to mp_from_sequence

---
 include/boost/mp11/algorithm.hpp | 10 +++----
 test/Jamfile                     |  1 +
 test/mp_from_sequence_2.cpp      | 45 ++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 5 deletions(-)
 create mode 100644 test/mp_from_sequence_2.cpp

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index 60987a8..d931457 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -308,20 +308,20 @@ template<class L, std::size_t N> using mp_drop_c = typename detail::mp_drop_impl
 
 template<class L, class N> using mp_drop = mp_drop_c<L, std::size_t{ N::value }>;
 
-// mp_from_sequence<S>
+// mp_from_sequence<S, F>
 namespace detail
 {
 
-template<class S> struct mp_from_sequence_impl;
+template<class S, class F> struct mp_from_sequence_impl;
 
-template<template<class T, T... I> class S, class U, U... J> struct mp_from_sequence_impl<S<U, J...>>
+template<template<class T, T... I> class S, class U, U... J, class F> struct mp_from_sequence_impl<S<U, J...>, F>
 {
-    using type = mp_list<std::integral_constant<U, J>...>;
+    using type = mp_list_c<U, (F::value + J)...>;
 };
 
 } // namespace detail
 
-template<class S> using mp_from_sequence = typename detail::mp_from_sequence_impl<S>::type;
+template<class S, class F = mp_int<0>> using mp_from_sequence = typename detail::mp_from_sequence_impl<S, F>::type;
 
 // mp_iota(_c)<N>
 template<std::size_t N> using mp_iota_c = mp_from_sequence<make_index_sequence<N>>;
diff --git a/test/Jamfile b/test/Jamfile
index f8344f6..661b801 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -109,6 +109,7 @@ run mp_erase.cpp ;
 run mp_with_index.cpp ;
 run mp_with_index_cx.cpp ;
 run mp_from_sequence.cpp ;
+run mp_from_sequence_2.cpp ;
 run mp_min_element.cpp ;
 run mp_min_element_q.cpp ;
 run mp_max_element.cpp ;
diff --git a/test/mp_from_sequence_2.cpp b/test/mp_from_sequence_2.cpp
new file mode 100644
index 0000000..5e3538a
--- /dev/null
+++ b/test/mp_from_sequence_2.cpp
@@ -0,0 +1,45 @@
+// Copyright 2017, 2023 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/mp11/algorithm.hpp>
+#include <boost/mp11/integral.hpp>
+#include <boost/mp11/integer_sequence.hpp>
+#include <boost/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+template<class T, T... I> struct S;
+
+template<char Ch> using mp_char = std::integral_constant<char, Ch>;
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_list_c;
+    using boost::mp11::mp_from_sequence;
+    using boost::mp11::mp_int;
+    using boost::mp11::mp_size_t;
+    using boost::mp11::make_integer_sequence;
+    using boost::mp11::make_index_sequence;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<S<int>, mp_int<-3>>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<S<int, 1>, mp_int<-3>>, mp_list<mp_int<-2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<S<int, 1, 3>, mp_int<-3>>, mp_list<mp_int<-2>, mp_int<0>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<S<int, 1, 3, 5>, mp_int<-3>>, mp_list<mp_int<-2>, mp_int<0>, mp_int<+2>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<S<char, 0, 3, 7>, mp_int<'0'>>, mp_list_c<char, '0', '3', '7'>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_integer_sequence<int, 0>, mp_int<-3>>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_integer_sequence<int, 1>, mp_int<-3>>, mp_list<mp_int<-3>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_integer_sequence<int, 2>, mp_int<-3>>, mp_list<mp_int<-3>, mp_int<-2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_integer_sequence<int, 3>, mp_int<-3>>, mp_list<mp_int<-3>, mp_int<-2>, mp_int<-1>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_integer_sequence<char, 5>, mp_size_t<'0'>>, mp_list_c<char, '0', '1', '2', '3', '4'>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_index_sequence<0>, mp_int<4>>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_index_sequence<1>, mp_int<4>>, mp_list<mp_size_t<4>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_index_sequence<2>, mp_int<4>>, mp_list<mp_size_t<4>, mp_size_t<5>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_from_sequence<make_index_sequence<3>, mp_int<4>>, mp_list<mp_size_t<4>, mp_size_t<5>, mp_size_t<6>>>));
+
+    return boost::report_errors();
+}