[GPU] Add texture_util::SwizzleSigns for later

src/xenia/gpu/texture_util.cc

@@ -340,6 +340,43 @@ int32_t GetTiledOffset3D(int32_t x, int32_t y, int32_t z, uint32_t width,
   return address;
 }
 
+uint32_t SwizzleSigns(const xenos::xe_gpu_texture_fetch_t& fetch,
+                      bool* any_unsigned_out, bool* any_signed_out) {
+  uint32_t signs = 0;
+  bool any_unsigned = false, any_signed = false;
+  // 0b00 or 0b01 for each component, whether it's constant 0/1.
+  uint32_t constant_mask = 0b00000000;
+  for (uint32_t i = 0; i < 4; ++i) {
+    uint32_t swizzle = (fetch.swizzle >> (i * 3)) & 0b111;
+    if (swizzle & 0b100) {
+      constant_mask |= 1 << (i * 2);
+    } else {
+      TextureSign sign =
+          TextureSign((fetch.dword_0 >> (2 + swizzle * 2)) & 0b11);
+      signs |= uint32_t(sign) << (i * 2);
+      if (sign == TextureSign::kSigned) {
+        any_signed = true;
+      } else {
+        any_unsigned = true;
+      }
+    }
+  }
+  if (any_signed && !any_unsigned) {
+    // If only signed and constant components, reading just from the signed host
+    // view is enough.
+    signs |= uint32_t(TextureSign::kSigned) * constant_mask;
+  } else {
+    signs |= uint32_t(TextureSign::kUnsigned) * constant_mask;
+  }
+  if (any_unsigned_out) {
+    *any_unsigned_out = any_unsigned;
+  }
+  if (any_signed_out) {
+    *any_signed_out = any_signed;
+  }
+  return signs;
+}
+
 }  // namespace texture_util
 }  // namespace gpu
 }  // namespace xe