x86: Add support routines to load and store 80-bit floats

The x87 FPU on x86 supports extended floating point. We currently
handle all floating point on x86 as double and don't support 80-bit
loads/stores. This changeset add a utility function to load and
convert 80-bit floats to doubles (loadFloat80) and another function to
store doubles as 80-bit floats (storeFloat80). Both functions use
libfputils to do the conversion in software. The functions are
currently not used, but are required to handle floating point in KVM
and to properly support all x87 loads/stores.

src/arch/x86/utility.cc

@@ -44,6 +44,7 @@
 #include "arch/x86/utility.hh"
 #include "arch/x86/x86_traits.hh"
 #include "cpu/base.hh"
+#include "fputils/fp80.h"
 #include "sim/system.hh"
 
 namespace X86ISA {
@@ -351,4 +352,20 @@ genX87Tags(uint16_t ftw, uint8_t top, int8_t spm)
     return ftw;
 }
 
+double
+loadFloat80(const void *_mem)
+{
+    const fp80_t *fp80((const fp80_t *)_mem);
+
+    return fp80_cvtd(*fp80);
+}
+
+void
+storeFloat80(void *_mem, double value)
+{
+    fp80_t *fp80((fp80_t *)_mem);
+
+    *fp80 = fp80_cvfd(value);
+}
+
 } // namespace X86_ISA

src/arch/x86/utility.hh

@@ -187,6 +187,22 @@ namespace X86ISA
      * @return New value of the FTW register.
      */
     uint16_t genX87Tags(uint16_t ftw, uint8_t top, int8_t spm);
+
+    /**
+     * Load an 80-bit float from memory and convert it to double.
+     *
+     * @param mem Pointer to an 80-bit float.
+     * @return double representation of the 80-bit float.
+     */
+    double loadFloat80(const void *mem);
+
+    /**
+     * Convert and store a double as an 80-bit float.
+     *
+     * @param mem Pointer to destination for the 80-bit float.
+     * @param value Double precision float to store.
+     */
+    void storeFloat80(void *mem, double value);
 }
 
 #endif // __ARCH_X86_UTILITY_HH__