abstract subtraction, set carry/overflow flags for subtraction

src/crab/arm/data_processing.cr

@@ -14,15 +14,15 @@ module ARM
     case opcode
     when 0x0 then res = @r[rd] = @r[rn] & operand_2
     when 0x1 then res = @r[rd] = @r[rn] ^ operand_2
-    when 0x2 then res = @r[rd] = @r[rn] &- operand_2
-    when 0x3 then res = @r[rd] = operand_2 &- @r[rn]
+    when 0x2 then res = @r[rd] = sub(@r[rn], operand_2, set_conditions)
+    when 0x3 then res = @r[rd] = sub(operand_2, @r[rn], set_conditions)
     when 0x4 then res = @r[rd] = @r[rn] &+ operand_2
     when 0x5 then res = @r[rd] = @r[rn] &+ operand_2 &+ @cpsr.carry.to_unsafe
     when 0x6 then res = @r[rd] = @r[rn] &- operand_2 &+ @cpsr.carry.to_unsafe &- 1
     when 0x7 then res = @r[rd] = operand_2 &- @r[rn] &+ @cpsr.carry.to_unsafe &- 1
     when 0x8 then res = @r[rn] & operand_2
     when 0x9 then res = @r[rn] ^ operand_2
-    when 0xA then res = @r[rn] &- operand_2
+    when 0xA then res = sub(@r[rn], operand_2, set_conditions)
     when 0xB then res = @r[rn] &+ operand_2
     when 0xC then res = @r[rd] = @r[rn] | operand_2
     when 0xD then res = @r[rd] = operand_2

src/crab/cpu.cr

@@ -110,6 +110,19 @@ class CPU
     word >> bits | word << (32 - bits)
   end
 
+  # Subtract two values
+  def sub(operand_1 : Word, operand_2 : Word, set_conditions) : Word
+    log "sub - operand_1:#{hex_str operand_1}, operand_2:#{hex_str operand_2}"
+    res = operand_1 &- operand_2
+    if set_conditions
+      @cpsr.overflow = bit?((operand_1 ^ operand_2) & (operand_1 ^ res), 31)
+      @cpsr.carry = operand_1 >= operand_2
+      @cpsr.zero = res == 0
+      @cpsr.negative = bit?(res, 31)
+    end
+    res
+  end
+
   def print_state(instr : Word) : Nil
     {% if flag? :trace %}
       @r.each do |reg|

src/crab/thumb/add_subtract.cr

@@ -11,7 +11,7 @@ module THUMB
                 @r[imm]
               end
     if sub
-      @r[rd] = @r[rs] &- operand
+      @r[rd] = sub(@r[rs], operand, true)
     else
       @r[rd] = @r[rs] &+ operand
     end

src/crab/thumb/alu_operations.cr

@@ -3,6 +3,7 @@ module THUMB
     op = bits(instr, 6..9)
     rs = bits(instr, 3..5)
     rd = bits(instr, 0..2)
+    # todo handle flags for all ops
     case op
     when 0b0000 then res = @r[rd] = @r[rd] & @r[rs]
     when 0b0001 then res = @r[rd] = @r[rd] ^ @r[rs]
@@ -14,7 +15,7 @@ module THUMB
     when 0b0111 then res = @r[rd] = ror(@r[rd], @r[rs], true)
     when 0b1000 then res = @r[rd] & @r[rs]
     when 0b1001 then res = @r[rd] = (-@r[rs].to_i32!).to_u32!
-    when 0b1010 then res = @r[rd] &- @r[rs]
+    when 0b1010 then res = sub(@r[rd], @r[rs], true)
     when 0b1011 then res = @r[rd] &+ @r[rs]
     when 0b1100 then res = @r[rd] = @r[rd] | @r[rs]
     when 0b1101 then res = @r[rd] = @r[rs] * @r[rd]

src/crab/thumb/move_compare_add_subtract.cr

@@ -6,9 +6,9 @@ module THUMB
     # todo handle carry flag on all ops
     case op
     when 0b00 then res = @r[rd] = offset
-    when 0b01 then res = @r[rd] &- offset
+    when 0b01 then res = sub(@r[rd], offset, true)
     when 0b10 then res = @r[rd] &+= offset
-    when 0b11 then res = @r[rd] &-= offset
+    when 0b11 then res = @r[rd] = sub(@r[rd], offset, true)
     else           raise "Invalid move/compare/add/subtract op: #{op}"
     end
     @cpsr.zero = res == 0