Add bitmap directory.

README.md

@@ -123,6 +123,15 @@ Linux installation and having to compile the Unix build of MicroPython.
 This describes ways of using the Pyboard to perform precision measurements of
 analog signals of up to around 50KHz. It is documented [here](./phase/README.md).
 
+# bitmap: bool arrays and sets of integers
+
+Classes for non-allocating handling of sets of small integers and small arrays
+of booleans. Legal member values for a set and array index values are
+constrained to 0 <= value <= max_value where max_value is a constructor arg.
+The set and the array are different ways of viewing a bitmap implemented as a
+bytearray: e.g. if max_value is 255 the bytearray occupies 32 bytes allocated by
+the constructor.
+
 # Pyboard D
 
 An unofficial guide to this board. When official docs emerge this will be

bitmap/bitmap.py

@@ -0,0 +1,137 @@
+# bitmap.py
+# Ideas for non-allocating classes based around a bitmap. Three classes are
+# presented:
+# IntSet: this is a set which is constrained to accept only integers in
+# a range 0 <= i <= maxval. Provides a minimal set of methods which can readily
+# be expanded.
+# SetByte: an even more minimal version of IntSet where the range is
+# 0 <= i <=255.
+# BoolList: A list of booleans. The list index is constrained to lie in range
+# 0 <= i <= maxval.
+
+class BitMap:
+    def __init__(self, maxval):
+        d, m = divmod(maxval, 8)
+        self._ba = bytearray(d + int(m > 0))
+        self._size = maxval
+
+    def _check(self, i):
+        if i < 0 or i >= self._size:
+            raise ValueError('Index out of range')
+
+    def _val(self, i):
+        self._check(i)
+        return (self._ba[i >> 3] & 1 << (i & 7)) > 0
+
+    def _set(self, i):
+        self._check(i)
+        self._ba[i >> 3] |= 1 << (i & 7)
+
+    def _clear(self, i):
+        self._check(i)
+        self._ba[i >> 3] &= ~(1 << (i &7))
+
+    # Iterate through an IntSet returning members
+    # Iterate through an IntList returning index value of True members
+    def __iter__(self):
+        for i in range(self._size):
+            if self._val(i):
+                yield i
+
+    # if MyIntSet:  True unless set is empty
+    # if MyBoolList: True if any element is True
+    def __bool__(self):
+        for x in self._ba:
+            if x:
+                return True
+        return False
+
+
+class IntSet(BitMap):
+    def __init__(self, maxval=256):
+        super().__init__(maxval)
+
+    # if n in MyIntSet:
+    def __contains__(self, i):
+        self._check(i)
+        return self._val(i)
+
+    # MyIntSet.discard(n)
+    def discard(self, i):
+        self._clear(i)
+
+    # MyIntSet.remove(n)
+    def remove(self, i):
+        if i in self:
+            self.discard(i)
+        else:
+            raise KeyError(i)
+
+    # MyIntSet.add(n)
+    def add(self, i):
+        self._set(i)
+
+    # Generator iterates through set intersection. Avoids allocation.
+    def intersec(self, other):
+        for i in other:
+            if i in self:
+                yield i
+
+class BoolList(BitMap):
+    def __init__(self, maxval=256):
+        super().__init__(maxval)
+
+    # MyBoolList[n] = True
+    def __setitem__(self, bit, val):
+        self._set(bit) if val else self._clear(bit)
+
+    # if MyBoolList[n]:
+    def __getitem__(self, bit):
+        return self._val(bit)
+
+    # if False in MyBoolList:
+    def __contains__(self, i):
+        if i:
+            for b in self._ba:
+                if b:
+                    return True
+        else:
+            for b in self._ba:
+                if not b:
+                    return True
+        return False
+
+
+# Minimal implementation of set for 0-255
+class SetByte:
+    def __init__(self):
+        self._ba = bytearray(32)
+
+    def __bool__(self):
+        for x in self._ba:
+            if x:
+                return True
+        return False
+
+    def __contains__(self, i):
+        return (self._ba[i >> 3] & 1 << (i & 7)) > 0
+
+    def discard(self, i):
+        self._ba[i >> 3] &= ~(1 << (i &7))
+
+    def add(self, i):
+        self._ba[i >> 3] |= 1 << (i & 7)
+
+# Test for set intersection
+bs = IntSet()
+bs.add(1)
+bs.add(2)
+1 in bs
+c = IntSet()
+c.add(1)
+c.add(4)
+c.add(5)
+g = bs.intersec(c)
+next(g)
+next(g)
+