expect addresses in literal immediates of branches

this is more useful than letting the immediate number simply pass through

lips/Dumper.lua

@@ -129,7 +129,15 @@ function Dumper:add_directive(fn, line, name, a, b)
 end
 
 function Dumper:desym(t)
-    if type(t.tok) == 'number' then
+    if t.tt == 'REL' then
+        local target = t.tok % 0x80000000
+        local pos = self.pos % 0x80000000
+        local rel = floor(target/4) - 1 - floor(pos/4)
+        if rel > 0x8000 or rel <= -0x8000 then
+            self:error('branch too far')
+        end
+        return rel % 0x10000
+    elseif type(t.tok) == 'number' then
         return t.tok
     elseif t.tt == 'REG' then
         assert(data.all_registers[t.tok], 'Internal Error: unknown register')

lips/Muncher.lua

@@ -116,8 +116,12 @@ function Muncher:const(relative, no_label)
         self:error('labels are not allowed here')
     end
     local t = self:token(self.t)
-    if relative and self.tt == 'LABELSYM' then
-        t.tt = 'LABELREL'
+    if relative then
+        if self.tt == 'LABELSYM' then
+            t.tt = 'LABELREL'
+        else
+            t.tt = 'REL'
+        end
     end
     self:advance()
     return t