rename bitmanip_inlines -> bitmanip

diff --git a/cldivrem.py b/cldivrem.py
new file mode 100644 (file)
index 0000000..5bf49b1
--- /dev/null
+++ b/cldivrem.py
@@ -0,0 +1,34 @@
+def cldivrem(n, d, width):
+    """ Carry-less Division and Remainder.
+        `n` and `d` are integers, `width` is the number of bits needed to hold
+        each input/output.
+        Returns a tuple `q, r` of the quotient and remainder.
+    """
+    assert d != 0, "TODO: decide what happens on division by zero"
+    assert 0 <= n < 1 << width, f"bad n (doesn't fit in {width}-bit uint)"
+    assert 0 <= d < 1 << width, f"bad d (doesn't fit in {width}-bit uint)"
+    r = n
+    q = 0
+    r_shift = 0
+    d_shift = 0
+    msb = 1 << (width - 1)
+    for _ in range(width):
+        if r & msb:
+            if d & msb:
+                r ^= d
+                q |= 1
+            else:
+                d <<= 1
+                d_shift += 1
+        else:
+            if d & msb:
+                r <<= 1
+                q <<= 1
+                r_shift += 1
+            else:
+                r <<= 1
+                r_shift += 1
+                d <<= 1
+                d_shift += 1
+    r >>= r_shift
+    return q, r