Lua: bit.rflagdecode

manual.lyx

@@ -1458,6 +1458,15 @@ Return string of length bits where ith character is ith character of on
  Out of range reads give last character, or '*'/'-' if empty.
 \end_layout
 
+\begin_layout Subsubsection
+bit.rflagdecode(number a, number bits, [string on, [string off]])
+\end_layout
+
+\begin_layout Standard
+Like bit.flagdecode, but outputs the string in the opposite order (most significa
+nt bit first).
+\end_layout
+
 \begin_layout Subsection
 Table gui:
 \end_layout

manual.txt

@@ -714,6 +714,12 @@ Return string of length bits where ith character is ith character
 of on if bit i is on, otherwise ith character of off. Out of 
 range reads give last character, or '*'/'-' if empty.
 
+8.2.18 bit.rflagdecode(number a, number bits, [string on, [string 
+  off]])
+
+Like bit.flagdecode, but outputs the string in the opposite order 
+(most significant bit first).
+
 8.3 Table gui:
 
 Most of these functions can only be called in on_paint and 

src/lua/bit.cpp

@@ -1,4 +1,5 @@
 #include "lua/internal.hpp"
+#include "library/minmax.hpp"
 
 #define BITWISE_BITS 48
 #define BITWISE_MASK ((1ULL << (BITWISE_BITS)) - 1)
@@ -204,7 +205,8 @@ namespace
 		return 2;
 	});
 
-	function_ptr_luafun lua_flagdecode(LS, "bit.flagdecode", [](lua_state& L, const std::string& fname) -> int {
+	int flagdecode_core(lua_state& L, const std::string& fname, bool reverse)
+	{
 		uint64_t a = L.get_numeric_argument<uint64_t>(1, fname.c_str());
 		uint64_t b = L.get_numeric_argument<uint64_t>(2, fname.c_str());
 		std::string on, off;
@@ -218,14 +220,23 @@ namespace
 		char offc = offl ? off[offl - 1] : '-';
 		char buffer[65];
 		unsigned i;
+		size_t bias = min(b, (uint64_t)64) - 1;
 		for(i = 0; i < 64 && i < b; i++) {
 			char onc2 = (i < onl) ? on[i] : onc;
 			char offc2 = (i < offl) ? off[i] : offc;
-			buffer[i] = ((a >> i) & 1) ? onc2 : offc2;
+			buffer[reverse ? (bias - i) : i] = ((a >> i) & 1) ? onc2 : offc2;
 		}
 		buffer[i] = '\0';
 		L.pushstring(buffer);
 		return 1;
+	}
+
+	function_ptr_luafun lua_flagdecode(LS, "bit.flagdecode", [](lua_state& L, const std::string& fname) -> int {
+		return flagdecode_core(L, fname, false);
+	});
+
+	function_ptr_luafun lua_rflagdecode(LS, "bit.rflagdecode", [](lua_state& L, const std::string& fname) -> int {
+		return flagdecode_core(L, fname, true);
 	});
 
 	lua_symmetric_bitwise<combine_none, BITWISE_MASK> bit_none("bit.none");