From 8538a0445a06a8f3979aa374d690843b770ed661 Mon Sep 17 00:00:00 2001
From: Matthew Berry <me@mattrb.com>
Date: Sun, 25 Oct 2020 14:07:00 -0700
Subject: [PATCH] properly handle rotating registers by an immediate,
 asr0=asr32

---
 src/crab/arm/arm.cr | 22 ++++++++++++----------
 src/crab/cpu.cr     |  5 ++++-
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/src/crab/arm/arm.cr b/src/crab/arm/arm.cr
index 5f4b8c3..eba06d0 100644
--- a/src/crab/arm/arm.cr
+++ b/src/crab/arm/arm.cr
@@ -71,18 +71,20 @@ module ARM
   def rotate_register(instr : Word, set_conditions : Bool, allow_register_shifts = true) : Word
     reg = bits(instr, 0..3)
     shift_type = bits(instr, 5..6)
-    shift_amount = if allow_register_shifts && bit?(instr, 4)
-                     shift_register = bits(instr, 8..11)
-                     # todo weird logic if bottom byte of reg > 31
-                     @r[shift_register] & 0xFF
-                   else
-                     bits(instr, 7..11)
-                   end
+    if allow_register_shifts && bit?(instr, 4)
+      shift_register = bits(instr, 8..11)
+      # todo weird logic if bottom byte of reg > 31
+      shift_amount = @r[shift_register] & 0xFF
+      immediate = false
+    else
+      shift_amount = bits(instr, 7..11)
+      immediate = true
+    end
     case shift_type
     when 0b00 then lsl(@r[reg], shift_amount, set_conditions)
-    when 0b01 then lsr(@r[reg], shift_amount, false, set_conditions)
-    when 0b10 then asr(@r[reg], shift_amount, false, set_conditions)
-    when 0b11 then ror(@r[reg], shift_amount, false, set_conditions)
+    when 0b01 then lsr(@r[reg], shift_amount, immediate, set_conditions)
+    when 0b10 then asr(@r[reg], shift_amount, immediate, set_conditions)
+    when 0b11 then ror(@r[reg], shift_amount, immediate, set_conditions)
     else           raise "Impossible shift type: #{hex_str shift_type}"
     end
   end
diff --git a/src/crab/cpu.cr b/src/crab/cpu.cr
index cbf89ab..4b234fa 100644
--- a/src/crab/cpu.cr
+++ b/src/crab/cpu.cr
@@ -171,7 +171,10 @@ class CPU
   # Arithmetic shift right
   def asr(word : Word, bits : Int, immediate : Bool, set_conditions : Bool) : Word
     log "asr - word:#{hex_str word}, bits:#{bits}"
-    return word if bits == 0
+    if bits == 0
+      return word unless immediate
+      bits = 32
+    end
     if bits <= 31
       @cpsr.carry = bit?(word, bits - 1) if set_conditions
       word >> bits | (0xFFFFFFFF_u32 &* (word >> 31)) << (32 - bits)