+uint8_t
+convX87TagsToXTags(uint16_t ftw)
+{
+ uint8_t ftwx(0);
+ for (int i = 0; i < 8; ++i) {
+ // Extract the tag for the current element on the FP stack
+ const unsigned tag((ftw >> (2 * i)) & 0x3);
+
+ /*
+ * Check the type of the current FP element. Valid values are:
+ * 0 == Valid
+ * 1 == Zero
+ * 2 == Special (Nan, unsupported, infinity, denormal)
+ * 3 == Empty
+ */
+ // The xsave version of the tag word only keeps track of
+ // whether the element is empty or not. Set the corresponding
+ // bit in the ftwx if it's not empty,
+ if (tag != 0x3)
+ ftwx |= 1 << i;
+ }
+
+ return ftwx;
+}
+
+uint16_t
+convX87XTagsToTags(uint8_t ftwx)
+{
+ uint16_t ftw(0);
+ for (int i = 0; i < 8; ++i) {
+ const unsigned xtag(((ftwx >> i) & 0x1));
+
+ // The xtag for an x87 stack position is 0 for empty stack positions.
+ if (!xtag) {
+ // Set the tag word to 3 (empty) for the current element.
+ ftw |= 0x3 << (2 * i);
+ } else {
+ // TODO: We currently assume that non-empty elements are
+ // valid (0x0), but we should ideally reconstruct the full
+ // state (valid/zero/special).
+ }
+ }
+
+ return ftw;
+}
+