Add num_in_numbits

3 files changed, 28 insertions, 3 deletions

diff --git a/coverage/backward.py b/coverage/backward.py
index 0df2a41e..34ab2f1a 100644
--- a/coverage/backward.py
+++ b/coverage/backward.py
@@ -114,6 +114,10 @@ if env.PY3:
         """Produce a byte string with the ints from `byte_values`."""
         return bytes(byte_values)
 
+    def byte_to_int(byte):
+        """Turn a byte indexed from a bytes object into an int."""
+        return byte
+
     def bytes_to_ints(bytes_value):
         """Turn a bytes object into a sequence of ints."""
         # In Python 3, iterating bytes gives ints.
@@ -132,6 +136,10 @@ else:
         """Produce a byte string with the ints from `byte_values`."""
         return "".join(chr(b) for b in byte_values)
 
+    def byte_to_int(byte):
+        """Turn a byte indexed from a bytes object into an int."""
+        return ord(byte)
+
     def bytes_to_ints(bytes_value):
         """Turn a bytes object into a sequence of ints."""
         for byte in bytes_value:
diff --git a/coverage/numbits.py b/coverage/numbits.py
index 19c328c4..c044073c 100644
--- a/coverage/numbits.py
+++ b/coverage/numbits.py
@@ -12,13 +12,13 @@ work with those binary blobs of data.
 
 """
 
-from coverage.backward import bytes_to_ints, binary_bytes, zip_longest
+from coverage.backward import byte_to_int, bytes_to_ints, binary_bytes, zip_longest
 from coverage.misc import contract
 
 
 @contract(nums='Iterable', returns='bytes')
 def nums_to_numbits(nums):
-    """Convert `nums` (an iterable of ints) into a numbits."""
+    """Convert `nums` (a non-empty iterable of ints) into a numbits."""
     nbytes = max(nums) // 8 + 1
     b = bytearray(nbytes)
     for num in nums:
@@ -46,3 +46,11 @@ def numbits_any_intersection(numbits1, numbits2):
     """Is there any number that appears in both numbits?"""
     byte_pairs = zip_longest(bytes_to_ints(numbits1), bytes_to_ints(numbits2), fillvalue=0)
     return any(b1 & b2 for b1, b2 in byte_pairs)
+
+@contract(num='int', numbits='bytes', returns='bool')
+def num_in_numbits(num, numbits):
+    """Does the integer `num` appear in `numbits`?"""
+    nbyte, nbit = divmod(num, 8)
+    if nbyte > len(numbits):
+        return False
+    return bool(byte_to_int(numbits[nbyte]) & (1 << nbit))
diff --git a/tests/test_numbits.py b/tests/test_numbits.py
index 4a835c4f..f4e52997 100644
--- a/tests/test_numbits.py
+++ b/tests/test_numbits.py
@@ -9,12 +9,14 @@ from hypothesis.strategies import sets, integers
 from coverage import env
 from coverage.numbits import (
     nums_to_numbits, numbits_to_nums, merge_numbits, numbits_any_intersection,
+    num_in_numbits,
     )
 
 from tests.coveragetest import CoverageTest
 
 # Hypothesis-generated line number data
-line_numbers = sets(integers(min_value=1, max_value=9999), min_size=1)
+line_number = integers(min_value=1, max_value=9999)
+line_numbers = sets(line_number, min_size=1)
 
 # When coverage-testing ourselves, hypothesis complains about a test being
 # flaky because the first run exceeds the deadline (and fails), and the second
@@ -47,3 +49,10 @@ class NumbitsOpTest(CoverageTest):
         inter = numbits_any_intersection(nums_to_numbits(nums1), nums_to_numbits(nums2))
         expect = bool(nums1 & nums2)
         self.assertEqual(expect, bool(inter))
+
+    @given(line_number, line_numbers)
+    @settings(default_settings)
+    def test_num_in_numbits(self, num, nums):
+        numbits = nums_to_numbits(nums)
+        is_in = num_in_numbits(num, numbits)
+        self.assertEqual(num in nums, is_in)