Contents

class xform_expr_mode

Enumeration class: the evaluation mode for an xform_expr .

Note that constants a, b, and c cannot be modified by a tranformation, so the value of an xform_expr representing an expression of the form (ax+b)/c can only change if x changes. There are two possible cases:

  • The memory location for which attribute x is extracted has changed. This can occur if the contents of locations along the access path (including the base symbol ) have changed.
  • The memory location is the same, but the value of attribute x is modified by the transformation.

Example:

int *p;
void f(){
    if( *p == 1 ){
        int i = 2;
        int j = 3;
        j = 4;
        *p = 5;
        *p = 6;
        p = &i;
        p = &j;
        return;
    }
}

If you were to query the value of *p using the step_xform covering the path from the start of the function to the return statement in these various modes, the results would be as follows.

xform_expr_mode Members

Constructors none
Static Method from_integer()
Methods __cmp__(), __eq__(), __ge__(), __gt__(), __hash__(), __le__(), __lt__(), __ne__(), __repr__(), __str__(), as_integer(), name()
Attributes POST, POST_DEREFS_PRE, POST_DEREFS_PRE_STRICT, POST_STRICT, PRE

xform_expr_mode Details

class cs.xform_expr_mode

Enumeration class: the evaluation mode for an xform_expr .

static from_integer(_inner)

Construct an instance from an integer representation.

Parameters:_inner (int) – The integer representation, as returned by xform_expr_mode.as_integer().
Return type:xform_expr_mode
Raises:result.ERROR_INVALID_ARGUMENT if _inner is not a valid integer representation for a xform_expr_mode instance.

Invariant: For xform_expr_mode x, xform_expr_mode.from_integer(x.as_integer()) == x

>>> xem = xform_expr_mode.POST_DEREFS_PRE_STRICT.as_integer()
>>> xem
4
>>> xform_expr_mode.from_integer(xem)
<cs.xform_expr_mode post_derefs_pre_strict>
__cmp__(other)

Comparison function for xform_expr_mode , with respect to a stable overall ordering.

Parameters:other (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:int
Returns:An integer N such that:
  • N==0 if the two objects compare equal
  • N<0 if self < other
  • N>0 if self > other
 
>>> xform_expr_mode.POST.__cmp__(xform_expr_mode.POST_DEREFS_PRE)
-1
__eq__(b)

Equality operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:True if self and b compare equal, False otherwise. 
>>> xform_expr_mode.POST_DEREFS_PRE_STRICT == xform_expr_mode.PRE
False
__ge__(b)

Greater-than-or-equal operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:True if self >= b , False otherwise. 
>>> xform_expr_mode.POST_STRICT >= xform_expr_mode.POST_DEREFS_PRE
True
__gt__(b)

Greater-than operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:True if self > b , False otherwise. 
>>> xform_expr_mode.POST_DEREFS_PRE_STRICT > xform_expr_mode.POST
True
__hash__()

Hash function for xform_expr_mode .

Return type:int 
>>> hash(xform_expr_mode.PRE)
0
__le__(b)

Less-than-or-equal operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:True if self <= b , False otherwise. 
>>> xform_expr_mode.POST_STRICT <= xform_expr_mode.POST_DEREFS_PRE
False
__lt__(b)

Less-than operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:True if self < b , False otherwise. 
>>> xform_expr_mode.PRE < xform_expr_mode.POST
True
__ne__(b)

Inequality operator for xform_expr_mode .

Parameters:b (xform_expr_mode) – The xform_expr_mode object to compare against.
Return type:bool
Returns:False if self and b compare equal, True otherwise. 
>>> xform_expr_mode.POST_DEREFS_PRE_STRICT != xform_expr_mode.POST
True
__repr__()

Get a representation of a xform_expr_mode object that includes information useful for debugging.

Return type:str
Returns:The string representation. 
>>> repr(xform_expr_mode.PRE)
'<cs.xform_expr_mode pre>'
__str__()

Get a simple string representation of a xform_expr_mode object.

Return type:str
Returns:The string representation. 
>>> str(xform_expr_mode.POST_STRICT)
'post_strict'
as_integer()

Get an integer representation of self.

Return type:int
Returns:An integer suitable for use with xform_expr_mode.from_integer().

Invariant: For xform_expr_mode x, xform_expr_mode.from_integer(x.as_integer()) == x

>>> xem = xform_expr_mode.POST_DEREFS_PRE_STRICT.as_integer()
>>> xem
4
>>> xform_expr_mode.from_integer(xem)
<cs.xform_expr_mode post_derefs_pre_strict>
name()

Get the name of a xform_expr_mode object.

Return type:str
Returns:The name. 
>>> xform_expr_mode.POST_DEREFS_PRE.name()
'post_derefs_pre'
POST

The expression should be evaluated using values of variables at the end of the transformation.

If the value of the expression is not modified in the transformation, the evaluated expression will be the same as it would have been with xform_expr_mode.PRE.

>>> xform_expr_mode.POST
<cs.xform_expr_mode post>
POST_DEREFS_PRE

The expression is evaluated as follows.

Let A be the memory location whose attribute x is used in the expression.

  • Address A is computed using the values of variables at the beginning of the transformation.
  • The expression is evaluated by taking the value of attribute x at address A at the end of the transformation.

If the value of the expression is not modified in the transformation, the evaluated expression will be the same as it would have been with xform_expr_mode.PRE.

>>> xform_expr_mode.POST_DEREFS_PRE
<cs.xform_expr_mode post_derefs_pre>
POST_DEREFS_PRE_STRICT

The expression is evaluated as specified for xform_expr_mode.POST_DEREFS_PRE.

If the value of the expression is not modified in the transformation, the query fails (as distinct from xform_expr_mode.POST_DEREFS_PRE, where the query proceeds).

>>> xform_expr_mode.POST_DEREFS_PRE_STRICT
<cs.xform_expr_mode post_derefs_pre_strict>
POST_STRICT

The expression should be evaluated using values of variables at the end of the transformation.

If the value of the expression is not modified in the transformation, the query fails (as distinct from xform_expr_mode.POST, where the query proceeds).

>>> xform_expr_mode.POST_STRICT
<cs.xform_expr_mode post_strict>
PRE

The expression should be evaluated using values of variables at the beginning of the transformation.

This can be useful for reasoning about constraints imposed on the original values later in the path (implied by ‘if’ statements for example).

(C API only: This is the recommended setting for constant-valued xform_expr (ax+b)/c with a==0.)

>>> xform_expr_mode.PRE
<cs.xform_expr_mode pre>