Allow RSSET to take a negative value (#2167)

test/asm/rs.asm

@@ -3,20 +3,20 @@ def a1 rb 1
 def a2 rw 1
 def a3 rl 1
 
-PRINTLN "a1 = ", a1
-PRINTLN "a2 = ", a2
-PRINTLN "a3 = ", a3
-PRINTLN "_RS = ", _RS
+PRINTLN "a1 = {d:a1}"
+PRINTLN "a2 = {d:a2}"
+PRINTLN "a3 = {d:a3}"
+PRINTLN "_RS = {d:_RS}"
 
 
 def b1 rb 1
 def b2 rw 1
 def b3 rl 1
 
-PRINTLN "b1 = ", b1
-PRINTLN "b2 = ", b2
-PRINTLN "b3 = ", b3
-PRINTLN "_RS = ", _RS
+PRINTLN "b1 = {d:b1}"
+PRINTLN "b2 = {d:b2}"
+PRINTLN "b3 = {d:b3}"
+PRINTLN "_RS = {d:_RS}"
 
 
 rsset 42
@@ -24,10 +24,10 @@ def c1 rb 1
 def c2 rw 1
 def c3 rl 1
 
-PRINTLN "c1 = ", c1
-PRINTLN "c2 = ", c2
-PRINTLN "c3 = ", c3
-PRINTLN "_RS = ", _RS
+PRINTLN "c1 = {d:c1}"
+PRINTLN "c2 = {d:c2}"
+PRINTLN "c3 = {d:c3}"
+PRINTLN "_RS = {d:_RS}"
 
 
 rsreset
@@ -35,7 +35,18 @@ def d1 rb 1
 def d2 rw 1
 def d3 rl 1
 
-PRINTLN "d1 = ", d1
-PRINTLN "d2 = ", d2
-PRINTLN "d3 = ", d3
-PRINTLN "_RS = ", _RS
+PRINTLN "d1 = {d:d1}"
+PRINTLN "d2 = {d:d2}"
+PRINTLN "d3 = {d:d3}"
+PRINTLN "_RS = {d:_RS}"
+
+
+rsset -10
+def e1 rb 1
+def e2 rw 1
+def e3 rl 1
+
+PRINTLN "e1 = {d:e1}"
+PRINTLN "e2 = {d:e2}"
+PRINTLN "e3 = {d:e3}"
+PRINTLN "_RS = {d:_RS}"

test/asm/rs.out

@@ -1,16 +1,20 @@
-a1 = $0
-a2 = $1
-a3 = $3
-_RS = $7
-b1 = $7
-b2 = $8
-b3 = $A
-_RS = $E
-c1 = $2A
-c2 = $2B
-c3 = $2D
-_RS = $31
-d1 = $0
-d2 = $1
-d3 = $3
-_RS = $7
+a1 = 0
+a2 = 1
+a3 = 3
+_RS = 7
+b1 = 7
+b2 = 8
+b3 = 10
+_RS = 14
+c1 = 42
+c2 = 43
+c3 = 45
+_RS = 49
+d1 = 0
+d2 = 1
+d3 = 3
+_RS = 7
+e1 = -10
+e2 = -9
+e3 = -7
+_RS = -3