From 55589ea0b0a4287201a618795b4e385d662e9f32 Mon Sep 17 00:00:00 2001
From: Matthew Berry <me@mattrb.com>
Date: Sun, 27 Sep 2020 17:00:21 -0700
Subject: [PATCH] thumb move shifted register (- carry flag)

diverges from armwrestler here bc of carry flag
---
 src/crab/thumb/move_shifted_register.cr | 17 +++++++++++++++++
 src/crab/thumb/thumb.cr                 |  2 +-
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 src/crab/thumb/move_shifted_register.cr

diff --git a/src/crab/thumb/move_shifted_register.cr b/src/crab/thumb/move_shifted_register.cr
new file mode 100644
index 0000000..a4e1281
--- /dev/null
+++ b/src/crab/thumb/move_shifted_register.cr
@@ -0,0 +1,17 @@
+module THUMB
+  def thumb_move_shifted_register(instr : Word) : Nil
+    # todo carry flags (currently first divergence on armwrestler)
+    op = bits(instr, 11..12)
+    offset = bits(instr, 6..10)
+    rs = bits(instr, 3..5)
+    rd = bits(instr, 0..2)
+    @r[rd] = case op
+             when 0b00 then @r[rs] << offset
+             when 0b01 then @r[rs] >> offset
+             when 0b10 then @r[rs] // (2 ** offset)
+             else           raise "Invalid shifted register op: #{op}"
+             end
+    @cpsr.zero = @r[rd] == 0
+    @cpsr.negative = bit?(@r[rd], 31)
+  end
+end
diff --git a/src/crab/thumb/thumb.cr b/src/crab/thumb/thumb.cr
index e05a54b..b0450c1 100644
--- a/src/crab/thumb/thumb.cr
+++ b/src/crab/thumb/thumb.cr
@@ -43,7 +43,7 @@ module THUMB
       elsif idx & 0b11111100 == 0b00011000
         # add/subtract
       elsif idx & 0b11100000 == 0b00000000
-        # move shifted register
+        lut[idx] = ->thumb_move_shifted_register(Word)
       end
     end
     lut