tests/float: Add test for exact float parsing.

dpgeorge · dpgeorge · commit e4af67667e40 · 2025-06-12T11:16:00.000+10:00
Thanks to @ddiminnie for the extra test cases. Signed-off-by: Damien George <damien@micropython.org>
diff --git a/tests/float/float_parse_doubleprec.py b/tests/float/float_parse_doubleprec.py
@@ -19,3 +19,32 @@
 print(float("1.00000000000000000000e-307"))
 print(float("10.0000000000000000000e-308"))
 print(float("100.000000000000000000e-309"))
+
+# ensure float is parsed exactly
+print(float("74e46"))
+
+# Overflow/largest double boundary:
+print(float("1.7976931348623159e308"))  # (should overflow, 0x000000000000f07f )
+print("%.15e" % float("1.7976931348623158e308"))  # (should yield the max double, 0xffffffffffffef7f )
+
+"""
+TODO get these working?
+# Normalized/denormalized double boundary
+print("%.16e" % float("2.2250738585072012e-308"))  # (should yield smallest normalized double, 0x0000000000001000 )
+print("%.16e" % float("2.2250738585072011e-308"))  # (should yield largest denormalized double, 0xffffffffffff0f00 )
+
+# Shortest (up to) 17-digit input that converts to smallest denormalized double:
+print(float("5e-324"))  # (should yield smallest denormalized double, 0x0100000000000000 )
+
+# Closest 17-digit input to the smallest denormalized double:
+print(float("4.9406564584124654e-324"))  # (should yield smallest denormalized double, 0x0100000000000000 )
+
+# The next boundary will depend on how good the ldexp implementation is on the target platform:
+# Smallest denormalized double/underflow boundary:
+
+print(float("2.4703282292062328e-324"))  # (should yield smallest denormalized double, 0x0100000000000000 )
+# (Note that this value is greater than 2**-1075 and therefore should round up. 64-bit CPython 3.7.5 on win32 gets this right. Your mileage may vary, since the 54 most significant bits of the result are 0b1.00000000000000000000000000000000000000000000000000000 x 2**-1075.)
+"""
+
+print(float("2.4703282292062327e-324"))  # (should underflow to zero: 0x0000000000000000 )
+# (Note that this value is less than 2**-1075 and therefore should round down to zero.)
