thumb add/subtract

src/crab/thumb/add_subtract.cr

@@ -0,0 +1,22 @@
+module THUMB
+  def thumb_add_subtract(instr : Word) : Nil
+    imm_flag = bit?(instr, 10)
+    sub = bit?(instr, 9)
+    imm = bits(instr, 6..8)
+    rs = bits(instr, 3..5)
+    rd = bits(instr, 0..2)
+    operand = if imm_flag
+                imm
+              else
+                @r[imm]
+              end
+    if sub
+      @r[rd] = @r[rs] &- operand
+    else
+      @r[rd] = @r[rs] &+ operand
+    end
+    # todo handle carry flag on all ops
+    @cpsr.zero = @r[rd] == 0
+    @cpsr.negative = bit?(@r[rd], 31)
+  end
+end

src/crab/thumb/thumb.cr

@@ -41,7 +41,7 @@ module THUMB
       elsif idx & 0b11100000 == 0b00100000
         lut[idx] = ->thumb_move_compare_add_subtract(Word)
       elsif idx & 0b11111100 == 0b00011000
-        # add/subtract
+        lut[idx] = ->thumb_add_subtract(Word)
       elsif idx & 0b11100000 == 0b00000000
         lut[idx] = ->thumb_move_shifted_register(Word)
       end