tools/src/cnf/optimize.go

// Copyright 2023 The Dawn & Tint Authors
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package cnf

import (
	"dawn.googlesource.com/dawn/tools/src/container"
)

// Optimize returns the expression with all duplicate unary expressions in the ORs removed, and
// with clauses that are supersets of other clauses removed (aka the Absorption Law).
// The returned expression is sorted.
func Optimize(e Expr) Expr {
	m := container.NewMap[Key, Ors]()
	for _, o := range e {
		b := unique(o)
		m.Add(b.Key(), b)
	}
	clauses := m.Values()

	var result Expr
	for i, a := range clauses {
		superset := false
		for j, b := range clauses {
			if i != j && isSubset(b, a) {
				superset = true
				break
			}
		}
		if !superset {
			result = append(result, a)
		}
	}
	return result
}

// isSubset returns true if all unary expressions in a are present in b.
func isSubset(a, b Ors) bool {
	if len(a) > len(b) {
		return false
	}
	m := make(map[Key]bool, len(b))
	for _, u := range b {
		m[u.Key()] = true
	}
	for _, u := range a {
		if !m[u.Key()] {
			return false
		}
	}
	return true
}

// unique returns the o with all duplicate unary expressions removed
// The returned OR expression list is sorted.
func unique(o Ors) Ors {
	m := container.NewMap[Key, Unary]()
	for _, u := range o {
		m.Add(u.Key(), u)
	}
	return m.Values()
}