Allow negative values to count macro arguments from the end (#1670)

include/asm/macro.hpp

@@ -9,11 +9,11 @@
 #include <vector>
 
 struct MacroArgs {
-	unsigned int shift;
+	uint32_t shift;
 	std::vector<std::shared_ptr<std::string>> args;
 
 	uint32_t nbArgs() const { return args.size() - shift; }
-	std::shared_ptr<std::string> getArg(uint32_t i) const;
+	std::shared_ptr<std::string> getArg(int32_t i) const;
 	std::shared_ptr<std::string> getAllArgs() const;
 
 	void appendArg(std::shared_ptr<std::string> arg);

man/rgbasm.5

@@ -1877,9 +1877,11 @@ being the second, and so on. Since there are only nine digits, you can only use
 To use the rest, you put the argument number in angle brackets, like
 .Ic \e<10> .
 .Pp
-This bracketed syntax supports decimal numbers and numeric symbols.
+This bracketed syntax supports decimal numbers and numeric symbols, where negative values count from the last argument.
 For example,
 .Ql \e<_NARG>
+or
+.Ql \e<-1>
 will get the last argument.
 .Pp
 Other macro arguments and symbol interpolations will also be expanded inside the angle brackets.

src/asm/lexer.cpp

@@ -625,13 +625,24 @@ static uint32_t readBracketedMacroArgNum() {
 		lexerState->disableInterpolation = disableInterpolation;
 	}};
 
-	uint32_t num = 0;
+	int32_t num = 0;
 	int c = peek();
 	bool empty = false;
 	bool symbolError = false;
+	bool negative = c == '-';
+
+	if (negative) {
+		shiftChar();
+		c = peek();
+	}
 
 	if (c >= '0' && c <= '9') {
-		num = readNumber(10, 0);
+		uint32_t n = readNumber(10, 0);
+		if (n > INT32_MAX) {
+			error("Number in bracketed macro argument is too large\n");
+			return 0;
+		}
+		num = negative ? -n : static_cast<int32_t>(n);
 	} else if (startsIdentifier(c) || c == '#') {
 		if (c == '#') {
 			shiftChar();
@@ -664,7 +675,7 @@ static uint32_t readBracketedMacroArgNum() {
 			num = 0;
 			symbolError = true;
 		} else {
-			num = sym->getConstantValue();
+			num = static_cast<int32_t>(sym->getConstantValue());
 		}
 	} else {
 		empty = true;
@@ -704,7 +715,7 @@ static std::shared_ptr<std::string> readMacroArg(char name) {
 		assume(str); // '\#' should always be defined (at least as an empty string)
 		return str;
 	} else if (name == '<') {
-		uint32_t num = readBracketedMacroArgNum();
+		int32_t num = readBracketedMacroArgNum();
 		if (num == 0) {
 			// The error was already reported by `readBracketedMacroArgNum`.
 			return nullptr;
@@ -718,7 +729,7 @@ static std::shared_ptr<std::string> readMacroArg(char name) {
 
 		auto str = macroArgs->getArg(num);
 		if (!str) {
-			error("Macro argument '\\<%" PRIu32 ">' not defined\n", num);
+			error("Macro argument '\\<%" PRId32 ">' not defined\n", num);
 		}
 		return str;
 	} else {

src/asm/macro.cpp

@@ -8,10 +8,16 @@
 
 #include "asm/warning.hpp"
 
-std::shared_ptr<std::string> MacroArgs::getArg(uint32_t i) const {
+std::shared_ptr<std::string> MacroArgs::getArg(int32_t i) const {
-	uint32_t realIndex = i + shift - 1;
+	// Bracketed macro arguments adjust negative indexes such that -1 is the last argument.
+	if (i < 0) {
+		i += args.size() + 1;
+	}
 
-	return realIndex >= args.size() ? nullptr : args[realIndex];
+	int32_t realIndex = i + shift - 1;
+
+	return realIndex < 0 || static_cast<uint32_t>(realIndex) >= args.size() ? nullptr
+	                                                                        : args[realIndex];
 }
 
 std::shared_ptr<std::string> MacroArgs::getAllArgs() const {

test/asm/negative-macro-args.asm

@@ -0,0 +1,21 @@
+MACRO mac
+	for i, -1, -_NARG - 1, -1
+		println "{d:i}: \<i> == \<{d:i}>"
+	endr
+	; error cases
+	def i = 0
+	println "{d:i}: \<i> == \<{d:i}>"
+	def i = -_NARG - 1
+	println "{d:i}: \<i> == \<{d:i}>"
+	def i = $7fff_ffff
+	println "{d:i}: \<i> == \<{d:i}>"
+	; signed/unsigned difference error cases
+	def i = $8000_0000
+	println "{d:i}: \<i> == \<{d:i}>"
+	println "{u:i}: \<i> == \<{u:i}>"
+	def i = $ffff_ffff
+	println "{d:i}: \<i> == \<{d:i}>"
+	println "{u:i}: \<i> == \<{u:i}>"
+ENDM
+
+mac A, B, C, D, E, F, G

test/asm/negative-macro-args.err

@@ -0,0 +1,26 @@
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(7):
+    Invalid bracketed macro argument '\<0>'
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(7):
+    Invalid bracketed macro argument '\<0>'
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(9):
+    Macro argument '\<-8>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(9):
+    Macro argument '\<-8>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(11):
+    Macro argument '\<2147483647>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(11):
+    Macro argument '\<2147483647>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(14):
+    Macro argument '\<-2147483648>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(14):
+    Number in bracketed macro argument is too large
+while expanding symbol "-2147483648"
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(15):
+    Macro argument '\<-2147483648>' not defined
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(15):
+    Number in bracketed macro argument is too large
+while expanding symbol "2147483648"
+error: negative-macro-args.asm(21) -> negative-macro-args.asm::mac(18):
+    Number in bracketed macro argument is too large
+while expanding symbol "4294967295"
+error: Assembly aborted (11 errors)!

test/asm/negative-macro-args.out

@@ -0,0 +1,14 @@
+-1: G == G
+-2: F == F
+-3: E == E
+-4: D == D
+-5: C == C
+-6: B == B
+-7: A == A
+0:  == 
+-8:  == 
+2147483647:  == 
+-2147483648:  == >
+2147483648:  == >
+-1: G == G
+4294967295: G == >