Added float_test.

Modified version from: http://forum.micropython.org/viewtopic.php?f=6&t=272

float_test.py

@@ -0,0 +1,75 @@
+import pyb
+import gc
+
+us = pyb.Timer(2, prescaler=83, period=0x7fffffff).counter
+clean = gc.collect
+begin = pyb.disable_irq
+end = pyb.enable_irq
+
+def test(code='pass', N=None, opt=None, irqOff=True, debug=False):
+    prefix = "@micropython.%s" % opt if opt else ""
+    begins, ends = ("begin()", "end()") if irqOff else ("", "")
+    wrap = "for i in range(%s): " % N if N else ""
+    testbench = ("""if 1:
+        %s
+        def _test():
+            %s%s; pass
+       
+        %s
+        def _ref():
+            %spass
+       
+        %s
+        clean()
+        t0 = us()
+        _test()
+        t1 = us()
+        clean()
+        t2 = us()
+        _ref()
+        t3 = us()
+        clean()
+        t4 = us()
+        %s
+        """ % (prefix, wrap, code, prefix, wrap, begins, ends))
+    if debug:
+        print(testbench)
+        return
+    exec(testbench)
+    dt = (t1-t0) - (t3-t2)
+    dtgc = (t2-t1) - (t4-t3)
+    return dt/N if N else dt, dtgc
+
+#test('1*1', 8192, debug=True)
+
+I = 1
+F = 1.
+def tabulate(opt=None, irqOff=True, ):
+    codes = "1*1", "I*I", "1.*1.", "F*F"
+    print("Time (us) measured using", opt or 'bytecode',
+          "without interrupts" if irqOff else "")
+    print("%6s"% 'counts', end="")
+    for code in codes:
+        print(" %5s %3s"% (code, 'gbc'), end="")
+    print()
+    for i in range(14):
+        print("%6d"% 2**i, end="")
+        for code in codes:
+            #if ((opt=='native' and
+            #     ("." in code and 2**i >= 64 or
+            #      "F" in code and 2**i >= 256)) or
+            #    (opt=='viper' and
+            #     ("1" in code and 2**i >= 1024 or
+            #      "I" in code and 2**i >= 1024 or
+            #      "." in code and 2**i >= 64 or
+            #      "F" in code and 2**i >= 256))):
+            #    # These cases bricked a pyboard
+            #    print("   bricked", end="")
+            #else:
+            print(" %5d %3d"% test(code, 2**i, opt), end="")
+        print()
+
+print("Hold USR button until GREEN+YELLOW after reset to recover bricked pyboard")
+for opt in (None, 'native', 'viper'):
+    tabulate(opt, opt!='viper')
+