From f9cbe6bc47dd4f5b8e85178caecd6f0de22b4c34 Mon Sep 17 00:00:00 2001 From: Dan Ellis Date: Tue, 12 Jul 2022 09:48:38 -0400 Subject: py/formatfloat: Format all whole-number floats exactly. Formerly, py/formatfloat would print whole numbers inaccurately with nonzero digits beyond the decimal place. This resulted from its strategy of successive scaling of the argument by 0.1 which cannot be exactly represented in floating point. The change in this commit avoids scaling until the value is smaller than 1, so all whole numbers print with zero fractional part. Fixes issue #4212. Signed-off-by: Dan Ellis dan.ellis@gmail.com --- tests/float/float_format_ints_doubleprec.py | 15 +++++++++++++++ 1 file changed, 15 insertions(+) create mode 100644 tests/float/float_format_ints_doubleprec.py (limited to 'tests/float/float_format_ints_doubleprec.py') diff --git a/tests/float/float_format_ints_doubleprec.py b/tests/float/float_format_ints_doubleprec.py new file mode 100644 index 0000000000..57899d6d65 --- /dev/null +++ b/tests/float/float_format_ints_doubleprec.py @@ -0,0 +1,15 @@ +# Test formatting of very large ints. +# Relies on double-precision floats. + +import array +import sys + +# Challenging way to express 1e200 and 1e100. +print("{:.12e}".format(float("9" * 400 + "e-200"))) +print("{:.12e}".format(float("9" * 400 + "e-300"))) + +# These correspond to the binary representation of 1e200 in float64s: +v1 = 0x54B249AD2594C37D # 1e100 +v2 = 0x6974E718D7D7625A # 1e200 +print("{:.12e}".format(array.array("d", v1.to_bytes(8, sys.byteorder))[0])) +print("{:.12e}".format(array.array("d", v2.to_bytes(8, sys.byteorder))[0])) -- cgit v1.2.3