From e8422c1c88a8e87781af0f786ff09300f694678f Mon Sep 17 00:00:00 2001
From: Rangi <35663410+Rangi42@users.noreply.github.com>
Date: Sat, 26 Sep 2026 13:10:39 -0400
Subject: [PATCH] Implement compound assignment operators `**=` and `>>>=`
 (#2158)

---
 man/rgbasm.5                     |  3 ++-
 src/asm/lexer.cpp                | 31 +++++++++++++++++++++----------
 src/asm/parser.y                 |  9 ++++++++-
 test/asm/compound-assignment.asm |  8 ++++++--
 test/asm/compound-assignment.err |  2 +-
 test/asm/compound-assignment.out |  8 ++++++--
 6 files changed, 44 insertions(+), 17 deletions(-)

diff --git a/man/rgbasm.5 b/man/rgbasm.5
index bbbe2c6b..c601953b 100644
--- a/man/rgbasm.5
+++ b/man/rgbasm.5
@@ -1485,7 +1485,8 @@ Variables can be conveniently redefined by compound assignment operators like in
 .It Sy Operator Ta Sy Meaning
 .It Li += -= Ta Compound plus/minus
 .It Li *= /= %= Ta Compound multiply/divide/modulo
-.It Li <<= >>= Ta Compound shift left/right
+.It Li **= Ta Compound exponent
+.It Li <<= >>= >>>= Ta Compound shift left/sign-extended right/zero-extended right
 .It Li &= \&|= ^= Ta Compound and/or/xor
 .El
 .Pp
diff --git a/src/asm/lexer.cpp b/src/asm/lexer.cpp
index 8d6dc4b8..2f560217 100644
--- a/src/asm/lexer.cpp
+++ b/src/asm/lexer.cpp
@@ -1683,9 +1683,6 @@ static Token yylex_NORMAL() {
 		case '-': // Either -= or SUB
 			return oneOrTwo('=', T_(POP_SUBEQ), T_(OP_SUB));
 
-		case '*': // Either *=, MUL, or EXP
-			return oneOrTwo('=', T_(POP_MULEQ), '*', T_(OP_EXP), T_(OP_MUL));
-
 		case '/': // Either /=, DIV, or a block comment
 			if (peek() == '*') {
 				shiftChar();
@@ -1716,6 +1713,14 @@ static Token yylex_NORMAL() {
 			}
 			return Token(T_(OP_LOGICNOT));
 
+		case '*': // Either *=, **=, MUL, or EXP
+			c = peek();
+			if (c == '*') {
+				shiftChar();
+				return oneOrTwo('=', T_(POP_EXPEQ), T_(OP_EXP));
+			}
+			return oneOrTwo('=', T_(POP_MULEQ), T_(OP_MUL));
+
 		case '<': // Either <<=, LT, LTE, or left shift
 			if (peek() == '<') {
 				shiftChar();
@@ -1723,13 +1728,6 @@ static Token yylex_NORMAL() {
 			}
 			return oneOrTwo('=', T_(OP_LOGICLE), T_(OP_LOGICLT));
 
-		case '>': // Either >>=, GT, GTE, or either kind of right shift
-			if (peek() == '>') {
-				shiftChar();
-				return oneOrTwo('=', T_(POP_SHREQ), '>', T_(OP_USHR), T_(OP_SHR));
-			}
-			return oneOrTwo('=', T_(OP_LOGICGE), T_(OP_LOGICGT));
-
 		case ':': // Either :, ::, or an anonymous label ref
 			c = peek();
 			if (c == '+' || c == '-') {
@@ -1737,6 +1735,19 @@ static Token yylex_NORMAL() {
 			}
 			return oneOrTwo(':', T_(DOUBLE_COLON), T_(COLON));
 
+			// Handle ambiguous 1-, 2-, 3-, or 4-char tokens
+
+		case '>': // Either >>=, >>>=, GT, GTE, or either kind of right shift
+			if (peek() == '>') {
+				shiftChar();
+				if (peek() == '>') {
+					shiftChar();
+					return oneOrTwo('=', T_(POP_USHREQ), T_(OP_USHR));
+				}
+				return oneOrTwo('=', T_(POP_SHREQ), T_(OP_SHR));
+			}
+			return oneOrTwo('=', T_(OP_LOGICGE), T_(OP_LOGICGT));
+
 			// Handle numbers
 
 		case '0': // Decimal, fixed-point, or base-prefix number
diff --git a/src/asm/parser.y b/src/asm/parser.y
index 27613a86..44a55d80 100644
--- a/src/asm/parser.y
+++ b/src/asm/parser.y
@@ -143,8 +143,9 @@
 %token POP_EQUAL "="
 %token POP_ADDEQ "+=" POP_SUBEQ "-="
 %token POP_MULEQ "*=" POP_DIVEQ "/=" POP_MODEQ "%="
+%token POP_EXPEQ "**="
 %token POP_ANDEQ "&=" POP_OREQ "|=" POP_XOREQ "^="
-%token POP_SHLEQ "<<=" POP_SHREQ ">>="
+%token POP_SHLEQ "<<=" POP_SHREQ ">>=" POP_USHREQ ">>>="
 
 // SM83 registers
 %token TOKEN_A "a"
@@ -640,6 +641,9 @@ compound_eq:
 	| POP_MODEQ {
 		$$ = RPN_MOD;
 	}
+	| POP_EXPEQ {
+		$$ = RPN_EXP;
+	}
 	| POP_XOREQ {
 		$$ = RPN_XOR;
 	}
@@ -655,6 +659,9 @@ compound_eq:
 	| POP_SHREQ {
 		$$ = RPN_SHR;
 	}
+	| POP_USHREQ {
+		$$ = RPN_USHR;
+	}
 ;
 
 align:
diff --git a/test/asm/compound-assignment.asm b/test/asm/compound-assignment.asm
index 5255ef55..03ac5d6a 100644
--- a/test/asm/compound-assignment.asm
+++ b/test/asm/compound-assignment.asm
@@ -11,8 +11,10 @@ println \2 ; 14
 println \2 ; 28
 {prefix}\2 /= 4
 println \2 ; 7
-{prefix}\2 %= 3
-println \2 ; 1
+{prefix}\2 %= 4
+println \2 ; 3
+{prefix}\2 **= 2
+println \2 ; 9
 {prefix}\2 |= 11
 println \2 ; 11
 {prefix}\2 ^= 12
@@ -23,6 +25,8 @@ println \2 ; 5
 println \2 ; 20
 {prefix}\2 >>= 1
 println \2 ; 10
+{prefix}\2 >>>= 1
+println \2 ; 5
 purge prefix
 endm
 
diff --git a/test/asm/compound-assignment.err b/test/asm/compound-assignment.err
index 19dfb866..f817228b 100644
--- a/test/asm/compound-assignment.err
+++ b/test/asm/compound-assignment.err
@@ -1,3 +1,3 @@
 error: Expected constant expression: undefined symbol `UnDeFiNeD`
-    at compound-assignment.asm(35)
+    at compound-assignment.asm(39)
 Assembly aborted with 1 error
diff --git a/test/asm/compound-assignment.out b/test/asm/compound-assignment.out
index c9d3f97c..6cc5cff8 100644
--- a/test/asm/compound-assignment.out
+++ b/test/asm/compound-assignment.out
@@ -4,23 +4,27 @@ $F
 $E
 $1C
 $7
-$1
+$3
+$9
 $B
 $7
 $5
 $14
 $A
+$5
 redef r:
 $A
 $F
 $E
 $1C
 $7
-$1
+$3
+$9
 $B
 $7
 $5
 $14
 $A
+$5
 $64
 $0