avrora.core.isdl.ast
Class BitRangeExpr

java.lang.Object
  avrora.core.isdl.ast.Expr
      avrora.core.isdl.ast.BitRangeExpr

public class BitRangeExpr

extends Expr

The BitRangeExpr class represents an expression whose value is the result of extracting a range of the bits from another expression. In the IR, ranges of bits can be specified for reading and writing, allowing cleaner expression of sub-byte fields. The bounds of these ranges are static: the endpoints must be constants.

Field Summary

int	high_bit The high_bit field represents the highest bit in the range to be extracted, inclusive.
int	low_bit The low_bit field represents the lowest bit in the range to be extracted, inclusive.
Expr	operand The operand field stores a reference to the expression that is the operand of the bit range expression, i.e. the value from which the range of bits will be extracted.

Fields inherited from class avrora.core.isdl.ast.Expr

PREC_A_ADD, PREC_A_AND, PREC_A_MUL, PREC_A_OR, PREC_A_SHIFT, PREC_A_XOR, PREC_L_AND, PREC_L_EQU, PREC_L_OR, PREC_L_REL, PREC_L_XOR, PREC_TERM, PREC_UN

Constructor Summary

BitRangeExpr(Expr o, int l, int h)
The constructor of the BitRangeExpr class simply initializes the references to the operands of the bit range expression.

BitRangeExpr(Expr o, Token l, Token h)
The constructor of the BitRangeExpr class simply initializes the references to the operands of the bit range expression.

Method Summary

Expr	accept(CodeRebuilder r) The accept() method implements one half of the visitor pattern for rebuilding of expressions.
void	accept(CodeVisitor v) The accept() method implements one half of the visitor pattern so that client visitors can traverse the syntax tree easily and in an extensible way.
void	accept(ExprVisitor v) The accept() method implements one half of the visitor pattern so that client visitors can traverse the syntax tree easily and in an extensible way.
int	getBitWidth() The getBitWidth() method gets the number of bits needed to represent this value.
int	getPrecedence() The getPrecedence() method gets the binding precedence for this expression.
boolean	isBitRangeExpr() The isBitRangeExpr() method tests whether the expression is an access of a range of bits.
boolean	isConstantExpr() The isConstantExpr() method tests whether this expression is a constant expression (i.e. it is reducable to a constant and has no references to variables, maps, etc).
java.lang.String	toString() The toString() method recursively converts this expression to a string.

Methods inherited from class avrora.core.isdl.ast.Expr

innerString, isLiteral, isMap, isVariable, tokenToBool, tokenToInt

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

operand

public final Expr operand

The operand field stores a reference to the expression that is the operand of the bit range expression, i.e. the value from which the range of bits will be extracted.

low_bit

public final int low_bit

The low_bit field represents the lowest bit in the range to be extracted, inclusive.

high_bit

public final int high_bit

The high_bit field represents the highest bit in the range to be extracted, inclusive.

Constructor Detail

BitRangeExpr

public BitRangeExpr(Expr o,
                    Token l,
                    Token h)

The constructor of the BitRangeExpr class simply initializes the references to the operands of the bit range expression.

Parameters:

o - a reference to the expression operand

l - the lowest bit in the range, inclusive

h - the highest bit in the range, inclusive

BitRangeExpr

public BitRangeExpr(Expr o,
                    int l,
                    int h)

The constructor of the BitRangeExpr class simply initializes the references to the operands of the bit range expression.

Parameters:

o - a reference to the expression operand

l - the lowest bit in the range, inclusive

h - the highest bit in the range, inclusive

Method Detail

getBitWidth

public int getBitWidth()

The getBitWidth() method gets the number of bits needed to represent this value. This is needed in the case of encoding formats, which need to compute the size of an instruction based on the width of its internal fields. For a BitRangeExpr, the number of bits required is statically known.

Overrides:

getBitWidth in class Expr

Returns:

the number of bits that this expression occupies

isConstantExpr

public boolean isConstantExpr()

The isConstantExpr() method tests whether this expression is a constant expression (i.e. it is reducable to a constant and has no references to variables, maps, etc).

Overrides:

isConstantExpr in class Expr

Returns:

true if this expression can be evaluated to a constant; false otherwise

isBitRangeExpr

public boolean isBitRangeExpr()

The isBitRangeExpr() method tests whether the expression is an access of a range of bits. This is used in pattern matching in some parts of the code.

Overrides:

isBitRangeExpr in class Expr

Returns:

true

accept

public void accept(ExprVisitor v)

The accept() method implements one half of the visitor pattern so that client visitors can traverse the syntax tree easily and in an extensible way.

Specified by:

accept in class Expr

Parameters:

v - the visitor to accept

accept

public void accept(CodeVisitor v)

The accept() method implements one half of the visitor pattern so that client visitors can traverse the syntax tree easily and in an extensible way.

Specified by:

accept in class Expr

Parameters:

v - the visitor to accept

accept

public Expr accept(CodeRebuilder r)

The accept() method implements one half of the visitor pattern for rebuilding of expressions. This visitor allows code to be slightly modified while only writing visit methods for the parts of the syntax tree affected.

Specified by:

accept in class Expr

Parameters:

r - the rebuilder to accept

Returns:

the result of calling the appropriate visit() method of the rebuilder

toString

public java.lang.String toString()

The toString() method recursively converts this expression to a string. For binary operations, inner expressions will be nested within parentheses if their precedence is lower than the precedence of the parent expression.

Returns:

a string representation of this expression

getPrecedence

public int getPrecedence()

The getPrecedence() method gets the binding precedence for this expression. This is used to compute when inner expressions must be nested within parentheses in order to preserve the implied order of evaluation.

Specified by:

getPrecedence in class Expr

Returns:

an integer representing the precedence of this expression; higher numbers are higher precedence