x86: pvclock: Move scale_delta into common header

The scale_delta function for shift / multiply with 31-bit
precision moves to a common header so it can be used by both
kernel and kvm module.

Signed-off-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 38 insertions, 0 deletions

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index cd02f324aa6..7f7e577a0e3 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -12,4 +12,42 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
                             struct pvclock_vcpu_time_info *vcpu,
                             struct timespec *ts);
 
+/*
+ * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
+ * yielding a 64-bit result.
+ */
+static inline u64 pvclock_scale_delta(u64 delta, u32 mul_frac, int shift)
+{
+        u64 product;
+#ifdef __i386__
+        u32 tmp1, tmp2;
+#endif
+
+        if (shift < 0)
+                delta >>= -shift;
+        else
+                delta <<= shift;
+
+#ifdef __i386__
+        __asm__ (
+                "mul  %5       ; "
+                "mov  %4,%%eax ; "
+                "mov  %%edx,%4 ; "
+                "mul  %5       ; "
+                "xor  %5,%5    ; "
+                "add  %4,%%eax ; "
+                "adc  %5,%%edx ; "
+                : "=A" (product), "=r" (tmp1), "=r" (tmp2)
+                : "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
+#elif defined(__x86_64__)
+        __asm__ (
+                "mul %%rdx ; shrd $32,%%rdx,%%rax"
+                : "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
+#else
+#error implement me!
+#endif
+
+        return product;
+}
+
 #endif /* _ASM_X86_PVCLOCK_H */