Add unsigned right shift operator

src/asm/lexer.c

@@ -1890,18 +1890,23 @@ static int yylex_NORMAL(void)
 				return T_OP_LOGICLT;
 			}
 
-		case '>': /* Either >>=, GT, GTE, or right shift */
+		case '>': /* Either >>=, GT, GTE, or either kind of right shift */
 			switch (peek()) {
 			case '=':
 				shiftChar();
 				return T_OP_LOGICGE;
 			case '>':
 				shiftChar();
-				if (peek() == '=') {
+				switch (peek()) {
+				case '=':
 					shiftChar();
 					return T_POP_SHREQ;
+				case '>':
+					shiftChar();
+					return T_OP_USHR;
+				default:
+					return T_OP_SHR;
 				}
-				return T_OP_SHR;
 			default:
 				return T_OP_LOGICGT;
 			}

src/asm/parser.y

@@ -534,7 +534,7 @@ enum {
 %token	T_OP_LOGICNE "!=" T_OP_LOGICEQU "=="
 %token	T_OP_ADD "+" T_OP_SUB "-"
 %token	T_OP_OR "|" T_OP_XOR "^" T_OP_AND "&"
-%token	T_OP_SHL "<<" T_OP_SHR ">>"
+%token	T_OP_SHL "<<" T_OP_SHR ">>" T_OP_USHR ">>>"
 %token	T_OP_MUL "*" T_OP_DIV "/" T_OP_MOD "%"
 %token	T_OP_NOT "~"
 %left	T_OP_LOGICOR
@@ -542,7 +542,7 @@ enum {
 %left	T_OP_LOGICGT T_OP_LOGICLT T_OP_LOGICGE T_OP_LOGICLE T_OP_LOGICNE T_OP_LOGICEQU
 %left	T_OP_ADD T_OP_SUB
 %left	T_OP_OR T_OP_XOR T_OP_AND
-%left	T_OP_SHL T_OP_SHR
+%left	T_OP_SHL T_OP_SHR T_OP_USHR
 %left	T_OP_MUL T_OP_DIV T_OP_MOD
 
 %precedence	NEG /* negation -- unary minus */
@@ -1477,6 +1477,9 @@ relocexpr_no_str : scoped_anon_id { rpn_Symbol(&$$, $1); }
 		| relocexpr T_OP_SHR relocexpr {
 			rpn_BinaryOp(RPN_SHR, &$$, &$1, &$3);
 		}
+		| relocexpr T_OP_USHR relocexpr {
+			rpn_BinaryOp(RPN_USHR, &$$, &$1, &$3);
+		}
 		| relocexpr T_OP_MUL relocexpr {
 			rpn_BinaryOp(RPN_MUL, &$$, &$1, &$3);
 		}

src/asm/rgbasm.5

@@ -251,7 +251,9 @@ A great number of operators you can use in expressions are available (listed fro
 .It Li ** Ta Exponent
 .It Li ~ + - Ta Unary complement/plus/minus
 .It Li * / % Ta Multiply/divide/modulo
-.It Li << >> Ta Shift left/right
+.It Li << Ta Shift left
+.It Li >> Ta Signed shift right (sign-extension)
+.It Li >>> Ta Unsigned shift right (zero-extension)
 .It Li & \&| ^ Ta Binary and/or/xor
 .It Li + - Ta Add/subtract
 .It Li != == <= >= < > Ta Comparison

src/asm/rpn.c

@@ -421,6 +421,19 @@ void rpn_BinaryOp(enum RPNCommand op, struct Expression *expr,
 
 			expr->val = op_shift_right(src1->val, src2->val);
 			break;
+		case RPN_USHR:
+			if (src2->val < 0)
+				warning(WARNING_SHIFT_AMOUNT,
+					"Shifting right by negative amount %" PRId32 "\n",
+					src2->val);
+
+			if (src2->val >= 32)
+				warning(WARNING_SHIFT_AMOUNT,
+					"Shifting right by large amount %" PRId32 "\n",
+					src2->val);
+
+			expr->val = op_shift_right_unsigned(src1->val, src2->val);
+			break;
 		case RPN_MUL:
 			expr->val = uleft * uright;
 			break;

src/link/patch.c

@@ -265,6 +265,10 @@ static int32_t computeRPNExpr(struct Patch const *patch,
 			value = popRPN();
 			value = op_shift_right(popRPN(), value);
 			break;
+		case RPN_USHR:
+			value = popRPN();
+			value = op_shift_right_unsigned(popRPN(), value);
+			break;
 
 		case RPN_BANK_SYM:
 			value = 0;

src/opmath.c

@@ -86,3 +86,18 @@ int32_t op_shift_right(int32_t value, int32_t amount)
 	// undefined, so use a left shift manually sign-extended
 	return ((uint32_t)value >> amount) | amount_high_bits;
 }
+
+int32_t op_shift_right_unsigned(int32_t value, int32_t amount)
+{
+	// Repeat the easy cases here to avoid INT_MIN funny business
+	if (amount == 0)
+		return value;
+	if (value == 0 || amount <= -32)
+		return 0;
+	if (amount > 31)
+		return (value < 0) ? -1 : 0;
+	if (amount < 0)
+		return op_shift_left(value, -amount);
+
+	return (uint32_t)value >> amount;
+}

src/rgbds.5

@@ -241,6 +241,7 @@ with some bytes being special prefixes for integers and symbols.
 .It Li $35 Ta Li <= comparison
 .It Li $40 Ta Li << operator
 .It Li $41 Ta Li >> operator
+.It Li $42 Ta Li >>> operator
 .It Li $50 Ta Li BANK(symbol) ,
 a
 .Ar LONG