From 48084b2a5e4ab48613b17c2a4cc2c9580c500ed7 Mon Sep 17 00:00:00 2001
From: Christian Zimmermann <christian.zimmermann@ur.de>
Date: Sat, 10 Apr 2021 00:58:30 +0200
Subject: [PATCH] generalize static_for.h

---
 src/include/statics/static_for.h | 77 ++++++++++++++------------------
 1 file changed, 33 insertions(+), 44 deletions(-)

diff --git a/src/include/statics/static_for.h b/src/include/statics/static_for.h
index fb12618..abc0c87 100644
--- a/src/include/statics/static_for.h
+++ b/src/include/statics/static_for.h
@@ -7,62 +7,51 @@
 namespace MultiArrayTools
 {
 
-    template <size_t BEG, size_t END>
+    template <size_t BEG, size_t END, size_t OFF>
     struct sfor
     {
-	template <typename F>
-	static void execs(const F& f)
+	template <typename Incr, typename F, typename Conc>
+	static inline auto exec(Incr incr, F f, Conc conc)
 	{
-	    if(BEG < END){
-		f(std::integral_constant<size_t, BEG>{});
-		sfor<BEG+1,END>::execs(f);
-	    }
+	    constexpr auto idx = std::integral_constant<size_t, BEG>{};
+	    constexpr auto idxm = std::integral_constant<size_t, BEG+OFF>{};
+	    static_assert(abs(idx.value - END) >= abs(incr(idx) - END),
+			  "this turns out to be a static endless loop");
+	    auto tmp = f(idxm);
+	    return conc(tmp, static_for<incr(idx),END,OFF>::exec(incr,f,conc));
 	}
-
-	template <typename F>
-	static void execsr(const F& f)
+	
+	template <typename Incr, typename F, typename Create, typename... Args>
+	static inline auto unpack(Incr incr, F f, Create create, const Args&... args)
 	{
-	    if(BEG < END){
-		f(std::integral_constant<size_t, END-1>{});
-		sfor<BEG,END-1>::execsr(f);
-	    }
-	}
-
-	template <typename F>
-	static void exec(const F& f)
-	{
-	    f(std::integral_constant<size_t, BEG>{});
-	    sfor<BEG+1,END>::exec(f);
-	}
-
-	template <typename F>
-	static void execr(const F& f)
-	{
-	    f(std::integral_constant<size_t, END-1>{});
-	    sfor<BEG,END-1>::execr(f);
+	    constexpr auto idx = std::integral_constant<size_t, BEG>{};
+	    constexpr auto idxm = std::integral_constant<size_t, BEG+OFF>{};
+	    static_assert(abs(idx.value - END) >= abs(incr(idx) - END),
+			  "this turns out to be a static endless loop");
+	    auto tmp = f(idxm);
+	    return static_for<incr(idx),END,OFF>::unpack(incr, f, create, args..., tmp);
 	}
     };
 
-    template <size_t N>
-    struct sfor<N,N>
+    template <size_t END, size_t OFF>
+    struct sfor<END,END,OFF>
     {
-	template <typename F>
-	static void execs(const F& f) {}
+	template <typename Incr, typename F, typename Conc>
+	static inline auto exec(Incr incr, F f, Conc conc)
+	{
+	    return 0;
+	}
 
-    	template <typename F>
-	static void execsr(const F& f) {}
-
-    	template <typename F>
-	static void exec(const F& f) {}
-
-    	template <typename F>
-	static void execr(const F& f) {}
+	template <typename Incr, typename F, typename Create, typename... Args>
+	static inline auto unpack(Incr incr, F f, Create create, const Args&... args)
+	{
+	    return create(args...);
+	}
     };
 }
 
-#define MA_SSFOR(i,beg,end,expr) MultiArrayTools::sfor<beg,end>::execs([&](auto i){ expr })
-#define MA_SSRFOR(i,end,beg,expr) MultiArrayTools::sfor<beg,end>::execsr([&](auto i){ expr })
-#define MA_SFOR(i,beg,end,expr) MultiArrayTools::sfor<beg,end>::exec([&](auto i){ expr })
-#define MA_SRFOR(i,end,beg,expr) MultiArrayTools::sfor<beg,end>::execr([&](auto i){ expr })
+#define MA_SFOR(i,beg,end,incr,expr) static_for<beg,end,0>::exec([&](auto i) constexpr { return incr; }, [&](auto i){ expr return 0; }, [&](auto f, auto next) { return 0; })
+#define MA_SRFOR(i,beg,end,decr,expr) static_for<beg,end,-1>::exec([&](auto i) constexpr { return decr; }, [&](auto i){ expr return 0; }, [&](auto f, auto next) { return 0; })
+#define MA_CFOR(i,beg,end,incr,expr,cre) static_for<beg,end,0>::unpack([&](auto i) constexpr { return incr; }, [&](auto i){ expr }, [&](auto... args) { return cre(args...); })
 
 #endif