From ac7e3bbe7280e68e4f0aeeb8d8e872c379624154 Mon Sep 17 00:00:00 2001
From: Matthew Berry <me@mattrb.com>
Date: Sun, 27 Sep 2020 23:32:14 -0700
Subject: [PATCH] thumb alu operations

---
 src/crab/thumb/alu_operations.cr | 28 ++++++++++++++++++++++++++++
 src/crab/thumb/thumb.cr          |  2 +-
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 src/crab/thumb/alu_operations.cr

diff --git a/src/crab/thumb/alu_operations.cr b/src/crab/thumb/alu_operations.cr
new file mode 100644
index 0000000..c191f9b
--- /dev/null
+++ b/src/crab/thumb/alu_operations.cr
@@ -0,0 +1,28 @@
+module THUMB
+  def thumb_alu_operations(instr : Word) : Nil
+    op = bits(instr, 6..9)
+    rs = bits(instr, 3..5)
+    rd = bits(instr, 0..2)
+    case op
+    when 0b0000 then res = @r[rd] = @r[rd] & @r[rs]
+    when 0b0001 then res = @r[rd] = @r[rd] ^ @r[rs]
+    when 0b0010 then res = @r[rd] = lsl(@r[rd], @r[rs], true)
+    when 0b0011 then res = @r[rd] = lsr(@r[rd], @r[rs], true)
+    when 0b0100 then res = @r[rd] = asr(@r[rd], @r[rs], true)
+    when 0b0101 then res = @r[rd] = @r[rd] &+ @r[rs] &+ @cpsr.carry.to_unsafe
+    when 0b0110 then res = @r[rd] = @r[rd] &- @r[rs] &- ~@cpsr.carry.to_unsafe
+    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 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]
+    when 0b1110 then res = @r[rd] = @r[rd] & ~@r[rs]
+    when 0b1111 then res = @r[rd] = ~@r[rs]
+    else             raise "Invalid alu op: #{op}"
+    end
+    @cpsr.zero = res == 0
+    @cpsr.negative = bit?(res, 31)
+  end
+end
diff --git a/src/crab/thumb/thumb.cr b/src/crab/thumb/thumb.cr
index 60efe5b..6dd4759 100644
--- a/src/crab/thumb/thumb.cr
+++ b/src/crab/thumb/thumb.cr
@@ -37,7 +37,7 @@ module THUMB
       elsif idx & 0b11111100 == 0b01000100
         # hi register operations / branch exchange
       elsif idx & 0b11111100 == 0b01000000
-        # alu operations
+        lut[idx] = ->thumb_alu_operations(Word)
       elsif idx & 0b11100000 == 0b00100000
         lut[idx] = ->thumb_move_compare_add_subtract(Word)
       elsif idx & 0b11111100 == 0b00011000