From 13f93325d3fe27722a24167aa14647848d8681f4 Mon Sep 17 00:00:00 2001
From: Jeff Epler <jepler@gmail.com>
Date: Mon, 22 Mar 2021 10:48:14 -0500
Subject: [PATCH] total_seconds: Fix precision problem
Since CircuitPython floats have very small precision, the "total_seconds"
method was not very useful for large timedeltas.
Instead of always returning a float, use pure-integer arithmetic (and
return an int) if either:
* the length of time is big (1<<21 is 2097152 seconds or about 24 days)
* the number of microseconds is zero
Otherwise, for small values with nonzero microseconds, use floating-point
math.
The cut-off point was chosen because in CircuitPython float arithmetic,
2097151.0+0.5 is different from 2097151.0, but 2097152.0+0.5 and
2097152.0 are *the same float*.
---
adafruit_datetime.py | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/adafruit_datetime.py b/adafruit_datetime.py
index cb4fef9..f3c442f 100755
--- a/adafruit_datetime.py
+++ b/adafruit_datetime.py
@@ -429,9 +429,15 @@ def microseconds(self):
# Instance methods
def total_seconds(self):
"""Return the total number of seconds contained in the duration."""
- return (
- (self._days * 86400 + self._seconds) * 10 ** 6 + self._microseconds
- ) / 10 ** 6
+ # If the duration is less than a threshold duration, and microseconds
+ # is nonzero, then the result is a float. Otherwise, the result is a
+ # (possibly long) integer. This differs from standard Python where the
+ # result is always a float, because the precision of CircuitPython
+ # floats is considerably smaller than on standard Python.
+ seconds = self._days * 86400 + self._seconds
+ if self._microseconds != 0 and abs(seconds) < (1 << 21):
+ seconds += self._microseconds / 10 ** 6
+ return seconds
def __repr__(self):
args = []