Add NHot function to expr module

pyeda/boolalg/expr.py

@@ -48,6 +48,7 @@
 
 * :func:`OneHot0`
 * :func:`OneHot`
+* :func:`NHot`
 * :func:`Majority`
 * :func:`AchillesHeel`
 * :func:`Mux`
@@ -495,6 +496,31 @@ def OneHot(*xs, simplify=True, conj=True):
     return _expr(y)
 
 
+def NHot(n, *xs, simplify=True):
+    """
+    Return an expression that means
+    "exactly N input functions are true".
+
+    If *simplify* is ``True``, return a simplified expression.
+    """
+    if not isinstance(n, int):
+        raise TypeError("expected n to be an int")
+    if not 0 <= n <= len(xs):
+        fstr = "expected 0 <= n <= {}, got {}"
+        raise ValueError(fstr.format(len(xs), n))
+
+    xs = {Expression.box(x).node for x in xs}
+    terms = list()
+    for hots in itertools.combinations(xs, n):
+        colds = xs - set(hots)
+        not_colds = tuple(map(exprnode.not_, colds))
+        terms.append(exprnode.and_(*(hots + not_colds)))
+    y = exprnode.or_(*terms)
+    if simplify:
+        y = y.simplify()
+    return _expr(y)
+
+
 def Majority(*xs, simplify=True, conj=False):
     """
     Return an expression that means

pyeda/inter.py

@@ -30,7 +30,7 @@
     exprvar, expr,
     ast2expr, expr2dimacscnf, expr2dimacssat, upoint2exprpoint,
     Not, Or, And, Nor, Nand, Xor, Xnor, Equal, Unequal, Implies, ITE,
-    Nor, Nand, OneHot0, OneHot, Majority, AchillesHeel,
+    Nor, Nand, OneHot0, OneHot, NHot, Majority, AchillesHeel,
     Mux, ForAll, Exists,
     Expression,
     NormalForm, DisjNormalForm, ConjNormalForm, DimacsCNF,