[Base] Support sign-extension in bitfield

2 files changed, 17 insertions, 16 deletions

diff --git a/src/xenia/base/bit_field.h b/src/xenia/base/bit_field.h
index 034f43d9e..98a8bfbf8 100644
--- a/src/xenia/base/bit_field.h
+++ b/src/xenia/base/bit_field.h
@@ -19,20 +19,28 @@ namespace xe {
 // Bitfield, where position starts at the LSB.
 template <typename T, size_t position, size_t n_bits>
 struct bf {
+  // For enum values, we strip them down to an underlying type.
+  typedef
+      typename std::conditional<std::is_enum<T>::value, std::underlying_type<T>,
+                                std::remove_reference<T>>::type::type
+          value_type;
+
   bf() = default;
   inline operator T() const { return value(); }
 
   inline T value() const {
-    return static_cast<T>((storage & mask()) >> position);
+    auto value = (storage & mask()) >> position;
+    if (std::is_signed<value_type>::value) {
+      // If the value is signed, sign-extend it.
+      value_type sign_mask = value_type(1) << (n_bits - 1);
+      value = (sign_mask ^ value) - sign_mask;
+    }
+
+    return static_cast<T>(value);
   }
 
-  // For enum values, we strip them down to an underlying type.
-  typedef
-      typename std::conditional<std::is_enum<T>::value, std::underlying_type<T>,
-                                std::remove_reference<T>>::type::type
-          value_type;
   inline value_type mask() const {
-    return (((value_type)~0) >> (8 * sizeof(value_type) - n_bits)) << position;
+    return ((value_type(1) << n_bits) - 1) << position;
   }
 
   value_type storage;
diff --git a/src/xenia/gpu/vulkan/vulkan_command_processor.cc b/src/xenia/gpu/vulkan/vulkan_command_processor.cc
index b4020bea8..52f5ba7fc 100644
--- a/src/xenia/gpu/vulkan/vulkan_command_processor.cc
+++ b/src/xenia/gpu/vulkan/vulkan_command_processor.cc
@@ -912,15 +912,8 @@ bool VulkanCommandProcessor::IssueCopy() {
   // vtx_window_offset_enable
   assert_true(regs[XE_GPU_REG_PA_SU_SC_MODE_CNTL].u32 & 0x00010000);
   uint32_t window_offset = regs[XE_GPU_REG_PA_SC_WINDOW_OFFSET].u32;
-  int16_t window_offset_x = window_offset & 0x7FFF;
-  int16_t window_offset_y = (window_offset >> 16) & 0x7FFF;
-  // Sign-extension
-  if (window_offset_x & 0x4000) {
-    window_offset_x |= 0x8000;
-  }
-  if (window_offset_y & 0x4000) {
-    window_offset_y |= 0x8000;
-  }
+  int32_t window_offset_x = window_regs->window_offset.window_x_offset;
+  int32_t window_offset_y = window_regs->window_offset.window_y_offset;
 
   uint32_t dest_texel_size = uint32_t(GetTexelSize(copy_dest_format));