internal/ceres/expression_ref.cc

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2019 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
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// Author: darius.rueckert@fau.de (Darius Rueckert)

#include "ceres/codegen/internal/expression_ref.h"
#include "glog/logging.h"

namespace ceres {
namespace internal {

ExpressionRef ExpressionRef::Create(ExpressionId id) {
  ExpressionRef ref;
  ref.id = id;
  return ref;
}

ExpressionRef::ExpressionRef(double compile_time_constant) {
  id = Expression::CreateCompileTimeConstant(compile_time_constant);
}

ExpressionRef::ExpressionRef(const ExpressionRef& other) { *this = other; }

ExpressionRef& ExpressionRef::operator=(const ExpressionRef& other) {
  // Assigning an uninitialized variable to another variable is an error.
  CHECK(other.IsInitialized()) << "Uninitialized Assignment.";
  if (IsInitialized()) {
    // Create assignment from other -> this
    Expression::CreateAssignment(this->id, other.id);
  } else {
    // Create a new variable and
    // Create assignment from other -> this
    // Passing kInvalidExpressionId to CreateAssignment generates a new variable
    // name which we store in the id.
    id = Expression::CreateAssignment(kInvalidExpressionId, other.id);
  }
  return *this;
}

ExpressionRef::ExpressionRef(ExpressionRef&& other) {
  *this = std::move(other);
}

ExpressionRef& ExpressionRef::operator=(ExpressionRef&& other) {
  // Assigning an uninitialized variable to another variable is an error.
  CHECK(other.IsInitialized()) << "Uninitialized Assignment.";

  if (IsInitialized()) {
    // Create assignment from other -> this
    Expression::CreateAssignment(id, other.id);
  } else {
    // Special case: 'this' is uninitialized and other is an rvalue.
    //    -> Implement copy elision by only setting the reference
    // This reduces the number of generated expressions roughly by a factor
    // of 2. For example, in the following statement:
    //   T c = a + b;
    // The result of 'a + b' is an rvalue reference to ExpressionRef. Therefore,
    // the move constructor of 'c' is called. Since 'c' is also uninitialized,
    // this branch here is taken and the copy is removed. After this function
    // 'c' will just point to the temporary created by the 'a + b' expression.
    // This is valid, because we don't have any scoping information and
    // therefore assume global scope for all temporary variables. The generated
    // code for the single statement above, is:
    //   v_2 = v_0 + v_1;   // With c.id = 2
    // Without this move constructor the following two lines would be generated:
    //   v_2 = v_0 + v_1;
    //   v_3 = v_2;        // With c.id = 3
    id = other.id;
  }
  other.id = kInvalidExpressionId;
  return *this;
}

// Compound operators
ExpressionRef& ExpressionRef::operator+=(const ExpressionRef& x) {
  *this = *this + x;
  return *this;
}

ExpressionRef& ExpressionRef::operator-=(const ExpressionRef& x) {
  *this = *this - x;
  return *this;
}

ExpressionRef& ExpressionRef::operator*=(const ExpressionRef& x) {
  *this = *this * x;
  return *this;
}

ExpressionRef& ExpressionRef::operator/=(const ExpressionRef& x) {
  *this = *this / x;
  return *this;
}

// Arith. Operators
ExpressionRef operator-(const ExpressionRef& x) {
  return ExpressionRef::Create(Expression::CreateUnaryArithmetic("-", x.id));
}

ExpressionRef operator+(const ExpressionRef& x) {
  return ExpressionRef::Create(Expression::CreateUnaryArithmetic("+", x.id));
}

ExpressionRef operator+(const ExpressionRef& x, const ExpressionRef& y) {
  return ExpressionRef::Create(
      Expression::CreateBinaryArithmetic("+", x.id, y.id));
}

ExpressionRef operator-(const ExpressionRef& x, const ExpressionRef& y) {
  return ExpressionRef::Create(
      Expression::CreateBinaryArithmetic("-", x.id, y.id));
}

ExpressionRef operator/(const ExpressionRef& x, const ExpressionRef& y) {
  return ExpressionRef::Create(
      Expression::CreateBinaryArithmetic("/", x.id, y.id));
}

ExpressionRef operator*(const ExpressionRef& x, const ExpressionRef& y) {
  return ExpressionRef::Create(
      Expression::CreateBinaryArithmetic("*", x.id, y.id));
}

ExpressionRef Ternary(const ComparisonExpressionRef& c,
                      const ExpressionRef& x,
                      const ExpressionRef& y) {
  return ExpressionRef::Create(
      Expression::CreateFunctionCall("Ternary", {c.id, x.id, y.id}));
}

#define CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(op)         \
  ComparisonExpressionRef operator op(const ExpressionRef& x,   \
                                      const ExpressionRef& y) { \
    return ComparisonExpressionRef(ExpressionRef::Create(       \
        Expression::CreateBinaryCompare(#op, x.id, y.id)));     \
  }

#define CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(op)                      \
  ComparisonExpressionRef operator op(const ComparisonExpressionRef& x,   \
                                      const ComparisonExpressionRef& y) { \
    return ComparisonExpressionRef(ExpressionRef::Create(                 \
        Expression::CreateBinaryCompare(#op, x.id, y.id)));               \
  }

CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(<)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(<=)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(>)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(>=)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(==)
CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR(!=)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(&&)
CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR(||)
#undef CERES_DEFINE_EXPRESSION_COMPARISON_OPERATOR
#undef CERES_DEFINE_EXPRESSION_LOGICAL_OPERATOR

ComparisonExpressionRef operator!(const ComparisonExpressionRef& x) {
  return ComparisonExpressionRef(
      ExpressionRef::Create(Expression::CreateLogicalNegation(x.id)));
}

}  // namespace internal
}  // namespace ceres