Refactor numbits into their own files

1 files changed, 42 insertions, 0 deletions

diff --git a/coverage/numbits.py b/coverage/numbits.py
new file mode 100644
index 00000000..bc29ed94
--- /dev/null
+++ b/coverage/numbits.py
@@ -0,0 +1,42 @@
+# Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0
+# For details: https://github.com/nedbat/coveragepy/blob/master/NOTICE.txt
+
+"""
+Functions to manipulate packed binary representations of number sets.
+
+To save space, coverage stores sets of line numbers in SQLite using a packed
+binary representation called a numbits.  A numbits is stored as a blob in the
+database.  The exact meaning of the bytes in the blobs should be considered an
+implementation detail that might change in the future.  Use these functions to
+work with those binary blobs of data.
+
+"""
+
+from coverage.backward import 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."""
+    nbytes = max(nums) // 8 + 1
+    b = bytearray(nbytes)
+    for num in nums:
+        b[num//8] |= 1 << num % 8
+    return bytes(b)
+
+@contract(numbits='bytes', returns='list[int]')
+def numbits_to_nums(numbits):
+    """Convert a numbits into a list of numbers."""
+    nums = []
+    for byte_i, byte in enumerate(bytes_to_ints(numbits)):
+        for bit_i in range(8):
+            if (byte & (1 << bit_i)):
+                nums.append(byte_i * 8 + bit_i)
+    return nums
+
+@contract(numbits1='bytes', numbits2='bytes', returns='bytes')
+def merge_numbits(numbits1, numbits2):
+    """Merge two numbits"""
+    byte_pairs = zip_longest(bytes_to_ints(numbits1), bytes_to_ints(numbits2), fillvalue=0)
+    return binary_bytes(b1 | b2 for b1, b2 in byte_pairs)