Sumador completo, suma: A XOR B XOR Cin
El bit de suma de un sumador completo, A XOR B XOR Cin, es la paridad impar de los dos bits de los operandos y el acarreo de entrada. Ocho filas, formas normales de cuatro términos, un mapa con cuatro unos aislados, 20 compuertas NAND.
Un sumador completo suma tres bits: los dos bits de los operandos, A y B, y el acarreo de entrada Cin de la etapa anterior. El bit de suma es 1 cuando un número impar de los tres es 1, así que es el XOR encadenado, y la lectura del motor dice exactamente eso: sum es verdadero cuando uno o tres de A, B y Cin son verdaderos. La tabla de verdad tiene ocho filas y la salida es verdadera en cuatro, Σm(1, 2, 4, 7).
Las comprobaciones: no es tautología, contraejemplo A = FALSO, B = FALSO, Cin = FALSO; es satisfacible, testigo A = FALSO, B = FALSO, Cin = VERDADERO. El simplificador no encontró ninguna ley que acorte la expresión de dos operadores. El conversor a formas normales, tras dos eliminaciones de XOR y dos distributividades, produce cuatro términos de tres literales en la FND, (A AND B AND Cin) OR (A AND NOT B AND NOT Cin) OR (NOT A AND B AND NOT Cin) OR (NOT A AND NOT B AND Cin), y cuatro cláusulas de tres literales en la FNC, doce literales cada una. El mapa de Karnaugh dibuja cuatro grupos de una celda, cuatro implicantes primos. Recuentos de compuertas: 20 NAND, 41 NOR.
Es la misma función que la página de paridad impar con otros nombres, y esa es la lección útil: la suma de un sumador es paridad. En hardware la cadena de dos XOR es el circuito de suma estándar, y la página del acarreo de salida aporta la otra salida. En software, un XOR de tres aparece en actualizaciones de sumas de comprobación y en el truco de intercambiar sin variable temporal. Lo que hay que vigilar es que ninguna reescritura AND-OR es más corta: cada término nombra las tres entradas, así que la forma XOR es la que conviene conservar en el código y en los diagramas.
sum := A XOR B XOR Cin · salida
Comprobaciones exactas
Tabla de verdad (8 filas)
| # | A | B | Cin | sum |
|---|---|---|---|---|
| 0 | FALSO | FALSO | FALSO | FALSO |
| 1 | FALSO | FALSO | VERDADERO | VERDADERO |
| 2 | FALSO | VERDADERO | FALSO | VERDADERO |
| 3 | FALSO | VERDADERO | VERDADERO | FALSO |
| 4 | VERDADERO | FALSO | FALSO | VERDADERO |
| 5 | VERDADERO | FALSO | VERDADERO | FALSO |
| 6 | VERDADERO | VERDADERO | FALSO | FALSO |
| 7 | VERDADERO | VERDADERO | VERDADERO | VERDADERO |
Lectura en lenguaje claro
Principiantesum es verdadero exactamente cuando un número impar entre A, B y Cin son verdaderos (1 o 3 de ellos).
En todos los demás casos, sum es falso.
Sobre los operadores:
- Una cadena de XOR es verdadera cuando un número impar de sus partes son verdaderas. Con tres partes, el caso en que las tres son verdaderas también cuenta: no significa «exactamente una».
Intermediosum es verdadero exactamente cuando un número impar entre A, B y Cin son verdaderos (1 o 3 de ellos).
En todos los demás casos, sum es falso.
Avanzadosum es verdadero exactamente cuando un número impar entre A, B y Cin son verdaderos (1 o 3 de ellos) [paridad: disyunción exclusiva n-aria ⊕].
En todos los demás casos, sum es falso.
Notación formal: A ⊕ B ⊕ Cin
Diagrama lógico
Simplificación paso a paso
El motor no encontró ninguna ley que acorte esta expresión; ya es tan corta como sus leyes de reescritura permiten.
A XOR B XOR Cin
Mapa de Karnaugh
- celdas m1
NOT A AND NOT B AND Cin - celdas m2
NOT A AND B AND NOT Cin - celdas m4
A AND NOT B AND NOT Cin - celdas m7
A AND B AND Cin
Mintérminos y maxtérminos
sum(A, B, Cin) = Σm(1, 2, 4, 7)sum(A, B, Cin) = ΠM(0, 3, 5, 6)Orden de variables: A, B, Cin · 8 filas
Formas normales
Forma normal conjuntiva (FNC)
(A OR B OR Cin) AND (A OR NOT B OR NOT Cin) AND (NOT A OR B OR NOT Cin) AND (NOT A OR NOT B OR Cin)4 cláusulas, 12 literales · complete · Eliminación de XOR ×2, Distributividad ×2
Forma normal disyuntiva (FND)
(A AND B AND Cin) OR (A AND NOT B AND NOT Cin) OR (NOT A AND B AND NOT Cin) OR (NOT A AND NOT B AND Cin)4 términos, 12 literales · complete · Eliminación de XOR ×2, Distributividad ×2
Solo NAND, solo NOR
Forma solo con NAND
NAND(NAND(NAND(NAND(A, NAND(B, B)), NAND(NAND(A, A), B)), NAND(Cin, Cin)), NAND(NAND(NAND(NAND(A, NAND(B, B)), NAND(NAND(A, A), B)), NAND(NAND(A, NAND(B, B)), NAND(NAND(A, A), B))), Cin))20 compuertas · equivalencia verificada en todas las filas
Forma solo con NOR
NOR(NOR(NOR(NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B))), Cin), NOR(NOR(NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B))), NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B)))), NOR(Cin, Cin))), NOR(NOR(NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B))), Cin), NOR(NOR(NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B))), NOR(NOR(NOR(A, A), B), NOR(A, NOR(B, B)))), NOR(Cin, Cin))))41 compuertas · equivalencia verificada en todas las filas
La misma regla como código
Python
# -*- coding: utf-8 -*-
# Generated by Tangibool (tangibool.python/1). Do not edit by hand; regenerate from the source revision.
# Model: not stated
# Source revision: reference
# Interpretation status: not stated
"""Tangibool evaluator (decision model).
Generated deterministically from the validated Boolean model; it evaluates exactly that
model. It does not establish that the model is a complete, legal, or safe statement of a
real-world rule, and evaluating examples does not verify the rule.
Source revision: reference
Interpretation status: not stated
Exporter: 1.0.0 (format tangibool.python/1; engine 1.0.0; semantics tangibool-semantics/1)
Logic digest: 8e6c62af347000f23fcb759e53e5bb3a263dc30c6fe85b4b32a23f8e6280dced
Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78
Inputs (dict keys, declared order) and generated parameter names:
'A' -> input_A
'B' -> input_B
'Cin' -> input_Cin
Outputs (declared order) and their functions:
'sum' -> output_sum(inputs)
Assumptions (the declared scope, checked by in_scope(inputs)):
none; every complete assignment is in scope.
Input contract:
Every required input must be exactly True or False (type(value) is bool). Missing
inputs, None, strings, integers (including 0 and 1), and keys that are not declared
inputs raise InputError before anything is evaluated, including inputs that a
short-circuiting operator would never read. Results are always bool.
Scope:
Decision functions raise OutOfScopeError when the inputs violate an assumption; an
out-of-scope assignment is never turned into a False result. Pass check_scope=False
to evaluate without the scope check, and use in_scope(inputs) to test it separately.
Usage:
import tangibool_model as model
model.evaluate({'A': False, 'B': False, 'Cin': False})
# -> {'sum': False}
model.output_sum({'A': False, 'B': False, 'Cin': False})
# -> False
model.evaluate({'A': 1, 'B': False, 'Cin': False})
# raises InputError: 1 is an int, not a bool
"""
import collections.abc as _abc
from typing import Dict, Mapping, Tuple
__all__ = [
"MODEL_INFO",
"IDENTIFIER_MAP",
"INPUT_NAMES",
"OUTPUT_NAMES",
"ASSUMPTIONS",
"InputError",
"OutOfScopeError",
"minterm_index",
"in_scope",
"evaluate",
"output_sum",
]
MODEL_INFO = {
"format": "tangibool.python/1",
"mode": "decision",
"model": None,
"revision": "reference",
"interpretation": None,
"exporter": "1.0.0",
"engine_version": "1.0.0",
"semantics_version": "tangibool-semantics/1",
"logic_digest": "8e6c62af347000f23fcb759e53e5bb3a263dc30c6fe85b4b32a23f8e6280dced",
"assumptions_digest": "d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78",
"primary_output": "sum",
"unused_inputs": (),
"subcircuits": (),
}
# Stable ID -> generated identifier (reversible mapping; names are exact, escaped strings).
IDENTIFIER_MAP = {
"v_702d37231f90": {"kind": "input", "name": "A", "identifier": "input_A"},
"v_244cf9fc1927": {"kind": "input", "name": "B", "identifier": "input_B"},
"v_8d0602f86684": {"kind": "input", "name": "Cin", "identifier": "input_Cin"},
"f_49fdbe6a7661": {"kind": "output", "name": "sum", "identifier": "output_sum"},
}
INPUT_NAMES = ("A", "B", "Cin")
OUTPUT_NAMES = ("sum",)
ASSUMPTIONS = ()
_DECLARED_INPUTS = frozenset(INPUT_NAMES)
_SCOPE_INPUTS = ()
_ASSUMPTION_FORMULAS = {entry["name"]: entry["formula"] for entry in ASSUMPTIONS}
class InputError(ValueError):
"""Raised when inputs are missing, undeclared, or not exactly True/False.
Every required input must satisfy type(value) is bool. Missing inputs, None, strings,
integers (including 0 and 1), and keys that are not declared inputs are rejected before
anything is evaluated. A missing input is never treated as False. The individual problems
are listed in the problems attribute.
"""
def __init__(self, problems):
self.problems = tuple(problems)
super().__init__("Invalid inputs: " + "; ".join(self.problems))
class OutOfScopeError(ValueError):
"""Raised when the inputs violate the model's assumptions (its declared scope).
Outside its assumptions the rule has no decision: this error is never a False result.
The names of the violated assumptions are in the violated attribute.
"""
def __init__(self, violated):
self.violated = tuple(violated)
details = ", ".join(name + " (" + _ASSUMPTION_FORMULAS.get(name, "?") + ")" for name in self.violated)
super().__init__(
"Out of scope: the inputs violate "
+ ("assumption " if len(self.violated) == 1 else "assumptions ")
+ details
+ ". The rule has no decision outside its assumptions; this is not a False result."
)
def _short_repr(value: object) -> str:
text = repr(value)
return text if len(text) <= 60 else text[:57] + "..."
def _checked_inputs(inputs: Mapping[str, bool], required: Tuple[str, ...], check_scope: bool) -> Dict[str, bool]:
"""Validate inputs strictly before anything is evaluated and return a plain copy."""
if type(check_scope) is not bool:
raise TypeError("check_scope must be True or False")
if not isinstance(inputs, _abc.Mapping):
raise InputError(["inputs must be a mapping from input names to True/False, got " + type(inputs).__name__])
problems = []
for key in inputs:
if type(key) is not str or key not in _DECLARED_INPUTS:
declared = ", ".join(repr(name) for name in INPUT_NAMES) or "none"
problems.append("undeclared input " + _short_repr(key) + " (declared inputs: " + declared + ")")
needed = tuple(required) + (_SCOPE_INPUTS if check_scope else ())
for name in needed:
if name not in inputs:
problems.append("missing required input " + repr(name))
for key, value in inputs.items():
if type(key) is str and key in _DECLARED_INPUTS and type(value) is not bool:
problems.append(
"input " + repr(key) + " must be True or False (type bool), got "
+ type(value).__name__ + " " + _short_repr(value)
)
if problems:
raise InputError(list(dict.fromkeys(problems)))
return dict(inputs.items())
def _require_bool_args(function: str, pairs: Tuple[Tuple[str, object], ...]) -> None:
problems = [
"argument " + repr(name) + " of " + function + " must be True or False (type bool), got "
+ type(value).__name__ + " " + _short_repr(value)
for name, value in pairs
if type(value) is not bool
]
if problems:
raise InputError(problems)
def minterm_index(*values: bool) -> int:
"""Row index of an assignment over a declared variable order.
The first value is the most significant bit, so all-False is row 0. Used for indexed
minterm (sum) and maxterm (product) forms.
"""
index = 0
for value in values:
if type(value) is not bool:
raise InputError(["minterm_index() takes True/False values, got " + type(value).__name__ + " " + _short_repr(value)])
index = index * 2 + (1 if value else 0)
return index
def _scope_values(values: Dict[str, bool]) -> Tuple[Tuple[str, bool], ...]:
"""Value of every enabled, confirmed assumption for validated inputs, in declared order."""
return ()
def _require_in_scope(values: Dict[str, bool]) -> None:
violated = tuple(name for name, holds in _scope_values(values) if not holds)
if violated:
raise OutOfScopeError(violated)
def in_scope(inputs: Mapping[str, bool]) -> bool:
"""True when the inputs satisfy every assumption (the model's declared scope).
Requires the inputs the assumptions read; raises InputError for invalid inputs.
"""
values = _checked_inputs(inputs, (), True)
return all(holds for _, holds in _scope_values(values))
# ---- Formula bodies (inputs are validated by the public functions below) ----
def _compute_output_sum(input_A: bool, input_B: bool, input_Cin: bool) -> bool:
"""Decision output 'sum': A XOR B XOR Cin"""
return (input_A != input_B) != input_Cin
# ---- Public API ----
def output_sum(inputs: Mapping[str, bool], *, check_scope: bool = True) -> bool:
"""Decision output 'sum' (stable ID f_49fdbe6a7661).
'sum' := A XOR B XOR Cin
Required inputs: 'A', 'B', 'Cin'.
Raises InputError for missing, undeclared, or non-bool inputs, and OutOfScopeError
when check_scope is True and the inputs violate an assumption.
"""
values = _checked_inputs(inputs, ("A", "B", "Cin"), check_scope)
if check_scope:
_require_in_scope(values)
output_sum_value = _compute_output_sum(values["A"], values["B"], values["Cin"])
return output_sum_value
def evaluate(inputs: Mapping[str, bool], *, check_scope: bool = True) -> Dict[str, bool]:
"""Evaluate every output (declared order); each output is computed once.
Required inputs: 'A', 'B', 'Cin'.
Raises InputError for missing, undeclared, or non-bool inputs, and OutOfScopeError
when check_scope is True and the inputs violate an assumption.
"""
values = _checked_inputs(inputs, ("A", "B", "Cin"), check_scope)
if check_scope:
_require_in_scope(values)
output_sum_value = _compute_output_sum(values["A"], values["B"], values["Cin"])
return {
"sum": output_sum_value,
}
PostgreSQL
-- Tangibool PostgreSQL export (tangibool.postgresql/1)
-- Target: PostgreSQL 16 or later with typed boolean inputs; tested with PostgreSQL 18.3 (PGlite 0.5.8).
-- Not a claim of compatibility with other SQL dialects.
-- Model: not stated
-- Source revision: reference
-- Interpretation status: not stated
-- Exporter: 1.0.0 (engine 1.0.0; semantics tangibool-semantics/1)
-- Logic digest: 8e6c62af347000f23fcb759e53e5bb3a263dc30c6fe85b4b32a23f8e6280dced
-- Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78
-- Mode: decision
--
-- Read-only: this file contains only WITH / VALUES / SELECT statements. No DDL, DML,
-- procedures, credentials, network access, or database changes. The expressions are pure
-- Boolean expressions, so their result does not depend on SQL evaluation order.
--
-- NON-NULL INPUT PRECONDITION: NULL is not a truth value of this rule. Every fragment below
-- is defined only when every input column it reads is a non-NULL boolean. The guard template
-- (section 2) marks any NULL input as 'invalid_input' and any row that violates the
-- assumptions as 'out_of_scope', and fills output columns only for 'ok' rows; a NULL in an
-- output column of another row is an envelope marker, not a third truth value. Never wrap
-- the fragments in COALESCE(..., FALSE) or otherwise choose a meaning for unknown inputs.
-- This evaluates the supplied model; it does not show that the model is a complete, legal,
-- or safe statement of a real-world rule.
--
-- Input columns (stable ID: name -> column):
-- v_702d37231f90: A -> "in_A"
-- v_244cf9fc1927: B -> "in_B"
-- v_8d0602f86684: Cin -> "in_Cin"
-- Output columns:
-- f_49fdbe6a7661: sum -> "out_sum"
-- Assumptions (scope K; exported separately and never folded into an output):
-- none; every complete input row is in scope.
-- ----------------------------------------------------------------------------------------------
-- 1. Expression fragments (parenthesised; non-NULL boolean inputs required)
-- ----------------------------------------------------------------------------------------------
--
-- [out_sum] output sum (stable ID f_49fdbe6a7661)
-- sum := A XOR B XOR Cin
-- PRECONDITION: "in_A", "in_B", "in_Cin" are non-NULL booleans.
-- (("in_A" <> "in_B") <> "in_Cin")
--
-- ----------------------------------------------------------------------------------------------
-- 2. Guard template (read-only SELECT over an inputs list)
-- ----------------------------------------------------------------------------------------------
-- Replace the example rows between the markers with your own rows, or replace the inputs
-- CTE with a SELECT that provides the boolean columns listed in the header. status is
-- 'invalid_input' when any input is NULL, 'out_of_scope' when the assumptions are false, and
-- 'ok' otherwise; output columns are filled only for 'ok' rows (NULL elsewhere is an
-- envelope marker). Assumption columns are shown for rows with complete inputs.
WITH inputs ("row_id", "in_A", "in_B", "in_Cin") AS (
-- tangibool:example-rows:begin
VALUES
(1, FALSE, FALSE, FALSE),
(2, FALSE, FALSE, TRUE),
(3, FALSE, TRUE, FALSE),
(4, FALSE, TRUE, TRUE),
(5, TRUE, FALSE, FALSE),
(6, TRUE, FALSE, TRUE),
(7, TRUE, TRUE, FALSE),
(8, TRUE, TRUE, TRUE),
(9, NULL::boolean, FALSE, FALSE)
-- tangibool:example-rows:end
),
checked AS (
SELECT
inputs.*,
CASE
WHEN "in_A" IS NULL OR "in_B" IS NULL OR "in_Cin" IS NULL THEN 'invalid_input'
ELSE 'ok'
END AS "status"
FROM inputs
)
SELECT
"row_id",
"in_A",
"in_B",
"in_Cin",
"status",
CASE WHEN "status" = 'ok' THEN (("in_A" <> "in_B") <> "in_Cin") END AS "out_sum"
FROM checked
ORDER BY "row_id";
SMT-LIB
; Tangibool SMT-LIB export (tangibool.smtlib/1) ; Profile: SMT-LIB 2.6 Boolean subset (QF_UF): Bool constants, define-fun, let, push/pop, assert, check-sat, echo. ; Tested with Z3 5.1.0 (z3-solver 5.2.0, WebAssembly build). ; Model: not stated ; Source revision: reference ; Interpretation status: not stated ; Exporter: 1.0.0 (engine 1.0.0; semantics tangibool-semantics/1) ; Logic digest: 8e6c62af347000f23fcb759e53e5bb3a263dc30c6fe85b4b32a23f8e6280dced ; Assumptions digest: d58ee1ad38e23e5093e4baa1047b5ae70d6972e08f555e34ac3fa16df63c4a78 ; Mode: decision ; ; Reading results: each query block states what sat and unsat mean for its question. A sat ; answer comes with a witness or counterexample (ask for it with (get-model) after sat only); ; unsat settles that scoped query and is solver-checked, not an independently checked proof ; certificate; unknown settles nothing. Blocks are scoped with push/pop, so assertions never ; accumulate across questions. This checks the supplied model, not whether it is a complete, ; legal, or safe statement of a real-world rule. ; ; Symbols (stable ID: name -> symbol): ; v_702d37231f90: A -> in_A ; v_244cf9fc1927: B -> in_B ; v_8d0602f86684: Cin -> in_Cin ; f_49fdbe6a7661: sum -> out_sum (set-option :produce-models true) (set-info :smt-lib-version 2.6) (set-logic QF_UF) ; ---- Inputs (declared order) (declare-const in_A Bool) ; A (declare-const in_B Bool) ; B (declare-const in_Cin Bool) ; Cin ; ---- Outputs (dependencies first) ; output sum (stable ID f_49fdbe6a7661): A XOR B XOR Cin (define-fun out_sum () Bool (xor (xor in_A in_B) in_Cin)) ; ---- Assumptions (the scope K; never folded into an output) ; K: conjunction of the enabled, confirmed assumptions (true when there are none) (define-fun K () Bool true) ; ---- Definitions only: nothing is asserted and no check is run. ; Add (assert ...) and (check-sat) inside (push 1) ... (pop 1) to ask a question.
LaTeX
sum = A \oplus B \oplus \mathit{Cin}El error habitual
Simplificar la suma a mano a una forma AND-OR esperando menos términos. El mapa muestra cuatro unos sin aristas compartidas, así que ningún par de mintérminos se fusiona, y la FND se queda en cuatro términos y doce literales. La forma de dos XOR ya es la más corta que las herramientas pueden mostrar.
Preguntas
¿Por qué el recuento NAND es 20 para dos compuertas XOR?
El conversor construye cada XOR con NAND y después construye el segundo XOR sobre el primero, duplicando subcircuitos como exige su construcción. Informa de 20 compuertas NAND y 41 NOR para esta expresión y vuelve a evaluar el resultado en las ocho filas antes de mostrarlo.
Relacionado
Operadores y compuertas
Herramientas
- Generador de tablas de verdad: cualquier expresión booleana, hasta 12 variables, con columnas intermedias
- Calculadora y simplificador de álgebra de Boole paso a paso (cada ley nombrada y verificada)
- Solucionador de mapas de Karnaugh: de 2 a 4 variables, agrupaciones, SOP y POS
Véase también
- Sumador completo, acarreo de salida: (A AND B) OR (Cin AND (A XOR B))
- Paridad impar de tres entradas: A XOR B XOR C
- Semisumador, suma: A XOR B
- Luz de escalera con tres interruptores: A XOR B XOR C
- Compuerta XOR: tabla de verdad de 2, 3 y 4 entradas (paridad impar)
- Lección 2: XOR: O exclusivo y paridad
Ejemplos resueltos
Generado a partir del motor de Tangibool, semántica tangibool-semantics/1, motor 1.0.0, compilación . Cada tabla, mapa, simplificación y veredicto de estas páginas lo calculó el motor de Tangibool al compilar el sitio, y cada afirmación la volvió a comprobar el mismo verificador exacto que usa la app. Los límites se indican donde aplican. © 2026 Foreranger LTD.