assign_lst Class Reference

#include <code_generation.h>

Public Member Functions
	assign_lst (const std::string &T, const std::string &temp_var_base_name)
	assign_lst (const std::string &T, const std::string &temp_var_base_name, const lst &lhs, const lst &rhs)
void	append (const ex &a, const ex &b)
void	prepend (const ex &a, const ex &b)
void	replace_common_subex (unsigned flag_type=subex_type::all)
void	split_large_subex (size_t nmax)
void	print (std::ostream &os) const
ex	get_temporary_variables () const

Private Member Functions
std::string	itos (int arg) const
bool	check_substitution_type (const ex &expr, unsigned flag_type) const
bool	check_large_subex (const ex &expr, size_t max_nops, lst &subexpr_lst) const
void	split_large_line (const ex &a, const ex &b, lst &new_lhs_lst, lst &new_rhs_lst, size_t max_nops)

Private Attributes
ex	lhs
	a list containing the l.h.s. of the assignment list
ex	rhs
	a list containing the r.h.s. of the assignment list
std::string	T
	string giving the data type in C of the expressions, usually something like "double" or "float".
std::string	temp_var_base_name
	string used as a base for labelling temporary variables.
std::vector< symbol >	temp_var
	vector holding intermediate variables, used internally.

Friends
std::ostream &	operator<< (std::ostream &os, const assign_lst &arg)

Detailed Description

A class which transforms a list of assignments into an equivalent list of assignments. The intention is that when these assignments are printed out as C code, the transformed ones will give "better" C code.

Methods to manipulate the assignment list are:

• replace_common_subex(unsigned flag), which replaces subexpressions, which occur syntactically more than once by temporary variables. The flag determines which classes from the set (add, mul, power, function) are considered for this substitution. The default is all of them.
• split_large_subex(size_t nmax), splits subexpressions with more than nmax operands into smaller pieces.

Data members: A list of assignments

 t0 = expr0;
 t1 = expr1;
  ...
 tn = exprn;

is stored in two lists

 lhs = lst(t0,t1,...,tn);
 rhs = lst(expr0,expr1,...,exprn);

T is a string giving the data type in C of the expressions, usually something like "double" or "float". When printing out the assignment list, T is printed in front of every assignment:

 T t0 = expr0;
 T t1 = expr1;
  ...

T can also be the empty string.

Intermediate variables obtain their names from temp_var_base_name, to which a serial number is attached, e.g. if temp_var_base_name=string("t"), the intermediate variables are labelled t0, t1, t2, etc..

temp_var is used only internally and is a vector holding the intermediate variables. A list of the additional intermediate variables can be obtained with the method get_temporary_variables().

Constructor & Destructor Documentation

assign_lst() [1/2]

assign_lst	(	const std::string &	arg_T,
		const std::string &	arg_temp_var_base_name
	)

Constructor.

T is initialised with arg_T, temp_var_base_name is initialised with arg_temp_var_base_name. lhs and rhs are empty.

assign_lst() [2/2]

assign_lst	(	const std::string &	arg_T,
		const std::string &	arg_temp_var_base_name,
		const lst &	arg_lhs,
		const lst &	arg_rhs
	)

Constructor.

T is initialised with arg_T, temp_var_base_name is initialised with arg_temp_var_base_name. lhs and rhs are initialised with arg_lhs and arg_rhs, respectively.

Member Function Documentation

append()

void append	(	const ex &	a,
		const ex &	b
	)

Appends the assignment a = b to the assignment list.

check_large_subex()

bool check_large_subex ( const ex &  expr, size_t  max_nops, lst &  subexpr_lst  ) const

private

Checks if expr contains large subexpressions of type add or mul with more than max_nops terms.

These large subexpressions are appended to subexpr_lst.

check_substitution_type()

bool check_substitution_type ( const ex &  expr, unsigned  flag_type  ) const

private

Checks if an expression can potentially be substituted.

The flag "flag_type" determines which classes from the set (add, mul, power, function) are considered for this substitution.

get_temporary_variables()

ex get_temporary_variables

(

)

const

Returns a list of the temporary variables.

itos()

std::string itos ( int  arg ) const

private

Helper function, which converts an integer into a string

prepend()

void prepend	(	const ex &	a,
		const ex &	b
	)

Prepends the assignment a = b to the assignment list.

print()

void print

(

std::ostream &

os

)

const

Print method: Prints the assignment list as C code.

replace_common_subex()

void replace_common_subex

(

unsigned

flag_type = subex_type::all

)

This function substitutes all subexpressions which occur syntactially more than once (in the sense of "subs") in the assignment list.

The function proceeds iteratively and substitutes first subexpressions, which are "closer" to the root of the expression tree. If these subexpressions in turn contain subsubexpressions, which occur multiple times, the latter are substituted in subsequent iterations.

split_large_line()

void split_large_line ( const ex &  a, const ex &  b, lst &  new_lhs_lst, lst &  new_rhs_lst, size_t  max_nops  )

private

Splits a single assignment into smaller pieces, if the right-hand-side contains a subexpression with more than max_nops operators.

The algorithm proceeds recursively, by introducing temporary variables for the first max_nops operands of the large subexpression and the remaining operands of the subexpression.

The assignments are appended to new_lhs_lst and new_rhs_lst. In the trivial case, where b does not contain any large subexpression, the method only appends a to new_lhs_lst and b to new_rhs_lst.

split_large_subex()

void split_large_subex

(

size_t

max_nops

)

This method splits subexpressions with more than max_nops operands into smaller pieces.

Friends And Related Function Documentation

operator<<

std::ostream & operator<< ( std::ostream &  os, const assign_lst &  arg  )

friend

Output operator. Prints the assignment list as C code.

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The documentation for this class was generated from the following files:

• code_generation.h
• code_generation.cc