Skip to content
Permalink
bcafcf8fc3
Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

micropython/tests/float/float_format_ints_doubleprec.py

Go to file
Dan Ellis py/formatfloat: Use pow(10, e) instead of pos/neg_pow lookup tables.
Latest commit 6f4d424 Jul 28, 2022 History 
Rework the conversion of floats to decimal strings so it aligns precisely
with the conversion of strings to floats in parsenum.c.  This is to avoid
rendering 1eX as 9.99999eX-1 etc.  This is achieved by removing the power-
of-10 tables and using pow() to compute the exponent directly, and that's
done efficiently by first estimating the power-of-10 exponent from the
power-of-2 exponent in the floating-point representation.

Code size is reduced by roughly 100 to 200 bytes by this commit.

Signed-off-by: Dan Ellis <dan.ellis@gmail.com>
0 contributors

Users who have contributed to this file

18 lines (14 sloc) 594 Bytes
Raw Blame
# 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]))
for i in range(300):
print(float("1e" + str(i)))