From 456fa49fa8e8acd43fb97fbaa4ab2eead3039be4 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Tue, 25 Feb 2020 09:54:25 -0500
Subject: [PATCH] Remove the float imprecision from the implementation
The new direct positive-path Hypothesis-based test wants to pass in huge
numbers and the float-based implementation does not do well for these inputs.
Happily, we can do better.
---
src/_zkapauthorizer/storage_common.py | 13 +++-------
.../tests/test_storage_protocol.py | 25 +++++++++++++++++++
2 files changed, 29 insertions(+), 9 deletions(-)
diff --git a/src/_zkapauthorizer/storage_common.py b/src/_zkapauthorizer/storage_common.py
index 78b8dc5..9bf9435 100644
--- a/src/_zkapauthorizer/storage_common.py
+++ b/src/_zkapauthorizer/storage_common.py
@@ -24,10 +24,6 @@ from base64 import (
b64encode,
)
-from math import (
- ceil,
-)
-
def _message_maker(label):
def make_message(storage_index):
return u"{label} {storage_index}".format(
@@ -59,17 +55,16 @@ def required_passes(bytes_per_pass, share_sizes):
:return int: The number of passes required to cover the storage cost.
"""
- result = int(
- ceil(
- sum(share_sizes, 0) / bytes_per_pass,
- ),
- )
if not isinstance(share_sizes, list):
raise TypeError(
"Share sizes must be a list of integers, got {!r} instead".format(
share_sizes,
),
)
+ result, b = divmod(sum(share_sizes, 0), bytes_per_pass)
+ if b:
+ result += 1
+
# print("required_passes({}, {}) == {}".format(bytes_per_pass, share_sizes, result))
return result
diff --git a/src/_zkapauthorizer/tests/test_storage_protocol.py b/src/_zkapauthorizer/tests/test_storage_protocol.py
index b0c83d7..d595e7c 100644
--- a/src/_zkapauthorizer/tests/test_storage_protocol.py
+++ b/src/_zkapauthorizer/tests/test_storage_protocol.py
@@ -51,6 +51,7 @@ from hypothesis import (
)
from hypothesis.strategies import (
sets,
+ lists,
tuples,
integers,
)
@@ -167,6 +168,30 @@ class RequiredPassesTests(TestCase):
raises(TypeError),
)
+ @given(
+ bytes_per_pass=integers(min_value=1),
+ expected_per_share=lists(integers(min_value=1), min_size=1),
+ )
+ def test_minimum_result(self, bytes_per_pass, expected_per_share):
+ """
+ ``required_passes`` returns an integer giving the fewest passes required
+ to pay for the storage represented by the given share sizes.
+ """
+ actual = required_passes(
+ bytes_per_pass,
+ list(
+ passes * bytes_per_pass
+ for passes
+ in expected_per_share
+ ),
+ )
+ self.assertThat(
+ actual,
+ Equals(sum(expected_per_share)),
+ )
+
+
+
class ShareTests(TestCase):
"""
Tests for interaction with shares.
--
GitLab