x86 asm: move x87 FPU instructions from x86-assembly-cheat

userland/arch/x86_64/fscale.S

@@ -0,0 +1,34 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#x86-x87-fpu-instructions */
+
+#include <lkmc.h>
+
+.data
+    double_1_0: .double 1.0
+    double_2_5: .double 2.5
+    double_4_0: .double 4.0
+LKMC_PROLOGUE
+    fldl double_4_0
+    # ST0 = 4.0
+
+    fldl double_2_5
+    # ST0 = 2.5
+    # ST1 = 4.0
+
+    fldl double_1_0
+    # ST0 = 1.0
+    # ST1 = 2.5
+    # ST2 = 4.0
+
+    # ST0 = 1 * 2 ^ (RoundTowardZero(2.5))
+    #     = 1 * 2 ^ 2
+    #     = 4
+    fscale
+    # ST0 = 4.0
+    # ST1 = 2.5
+    # ST2 = 4.0
+
+    fcomip %st(2)
+    # ST0 = 4.0
+    # ST1 = 2.5
+    LKMC_ASSERT(je)
+LKMC_EPILOGUE