From 99070f7f5c92a7ffea03bf72804f971f52562015 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 14 May 2023 03:49:28 +0300
Subject: [PATCH] Add a 'from' parameter to mp_iota, mp_iota_c. Refs #78.

---
 include/boost/mp11/algorithm.hpp |  6 +++---
 test/Jamfile                     |  1 +
 test/mp_iota_2.cpp               | 37 ++++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 test/mp_iota_2.cpp

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index d931457..b5508e6 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -323,9 +323,9 @@ template<template<class T, T... I> class S, class U, U... J, class F> struct mp_
 
 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>>;
-template<class N> using mp_iota = mp_from_sequence<make_integer_sequence<typename std::remove_const<decltype(N::value)>::type, N::value>>;
+// mp_iota(_c)<N, F>
+template<std::size_t N, std::size_t F = 0> using mp_iota_c = mp_from_sequence<make_index_sequence<N>, mp_size_t<F>>;
+template<class N, class F = mp_int<0>> using mp_iota = mp_from_sequence<make_integer_sequence<typename std::remove_const<decltype(N::value)>::type, N::value>, F>;
 
 // mp_at(_c)<L, I>
 namespace detail
diff --git a/test/Jamfile b/test/Jamfile
index 661b801..4a308a8 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -68,6 +68,7 @@ run mp_repeat.cpp ;
 run mp_product.cpp ;
 run mp_drop.cpp ;
 run mp_iota.cpp ;
+run mp_iota_2.cpp ;
 run mp_at.cpp ;
 run mp_at_sf.cpp : : : <toolset>gcc-4.7:<warnings>all ;
 run mp_take.cpp ;
diff --git a/test/mp_iota_2.cpp b/test/mp_iota_2.cpp
new file mode 100644
index 0000000..f1a0f07
--- /dev/null
+++ b/test/mp_iota_2.cpp
@@ -0,0 +1,37 @@
+// Copyright 2015, 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/core/lightweight_test_trait.hpp>
+#include <type_traits>
+
+int main()
+{
+    using boost::mp11::mp_list;
+    using boost::mp11::mp_iota;
+    using boost::mp11::mp_iota_c;
+    using boost::mp11::mp_int;
+    using boost::mp11::mp_size_t;
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota_c<0, 7>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota_c<1, 7>, mp_list<mp_size_t<7>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota_c<2, 7>, mp_list<mp_size_t<7>, mp_size_t<8>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota_c<3, 7>, mp_list<mp_size_t<7>, mp_size_t<8>, mp_size_t<9>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota_c<4, 7>, mp_list<mp_size_t<7>, mp_size_t<8>, mp_size_t<9>, mp_size_t<10>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_size_t<0>, mp_int<4>>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_size_t<1>, mp_int<4>>, mp_list<mp_size_t<4>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_size_t<2>, mp_int<4>>, mp_list<mp_size_t<4>, mp_size_t<5>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_size_t<3>, mp_int<4>>, mp_list<mp_size_t<4>, mp_size_t<5>, mp_size_t<6>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_size_t<4>, mp_int<4>>, mp_list<mp_size_t<4>, mp_size_t<5>, mp_size_t<6>, mp_size_t<7>>>));
+
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_int<0>, mp_int<-2>>, mp_list<>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_int<1>, mp_int<-2>>, mp_list<mp_int<-2>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_int<2>, mp_int<-2>>, mp_list<mp_int<-2>, mp_int<-1>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_int<3>, mp_int<-2>>, mp_list<mp_int<-2>, mp_int<-1>, mp_int<0>>>));
+    BOOST_TEST_TRAIT_TRUE((std::is_same<mp_iota<mp_int<4>, mp_int<-2>>, mp_list<mp_int<-2>, mp_int<-1>, mp_int<0>, mp_int<+1>>>));
+
+    return boost::report_errors();
+}