CBMC
string_constraint_generator.h File Reference

Generates string constraints to link results from string functions with their arguments. More...

#include <limits>
#include <solvers/strings/string_constraint.h>
#include <util/constexpr.def>
#include <util/deprecate.h>
#include <util/namespace.h>
#include <util/refined_string_type.h>
#include <util/replace_expr.h>
#include <util/string_expr.h>
#include "array_pool.h"
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Classes

struct  string_constraintst
 Collection of constraints of different types: existential formulas, universal formulas, and "not contains" (universal with one alternation). More...
 
class  string_constraint_generatort
 
struct  string_constraint_generatort::parseint_argumentst
 Argument block for parseInt and cousins, common to parseInt itself and CProverString.isValidInt. More...
 

Functions

void merge (string_constraintst &result, string_constraintst other)
 Merge two sets of constraints by appending to the first one. More...
 
exprt length_constraint_for_concat_char (const array_string_exprt &res, const array_string_exprt &s1, array_poolt &array_pool)
 Add axioms enforcing that the length of res is that of the concatenation of s1 with. More...
 
exprt length_constraint_for_concat (const array_string_exprt &res, const array_string_exprt &s1, const array_string_exprt &s2, array_poolt &array_pool)
 Add axioms enforcing that the length of res is that of the concatenation of s1 with s2 More...
 
exprt length_constraint_for_concat_substr (const array_string_exprt &res, const array_string_exprt &s1, const array_string_exprt &s2, const exprt &start, const exprt &end, array_poolt &array_pool)
 Add axioms enforcing that the length of res is that of the concatenation of s1 with the substring of s2 starting at index ‘start’ and ending at indexend'‘. More...
 
size_t max_printed_string_length (const typet &type, unsigned long ul_radix)
 Calculate the string length needed to represent any value of the given type using the given radix. More...
 
exprt is_positive (const exprt &x)
 
exprt minimum (const exprt &a, const exprt &b)
 
exprt maximum (const exprt &a, const exprt &b)
 
exprt sum_overflows (const plus_exprt &sum)
 
signedbv_typet get_return_code_type ()
 
exprt zero_if_negative (const exprt &expr)
 Returns a non-negative version of the argument. More...
 
exprt is_digit_with_radix (const exprt &chr, const bool strict_formatting, const exprt &radix_as_char, const unsigned long radix_ul)
 Check if a character is a digit with respect to the given radix, e.g. More...
 
exprt get_numeric_value_from_character (const exprt &chr, const typet &char_type, const typet &type, const bool strict_formatting, unsigned long radix_ul)
 Get the numeric value of a character, assuming that the radix is large enough. More...
 

Detailed Description

Generates string constraints to link results from string functions with their arguments.

This is inspired by the PASS paper at HVC'13: "PASS: String Solving with Parameterized Array and Interval Automaton" by Guodong Li and Indradeep Ghosh, which gives examples of constraints for several functions.

Definition in file string_constraint_generator.h.

Function Documentation

◆ get_numeric_value_from_character()

exprt get_numeric_value_from_character ( const exprt chr,
const typet char_type,
const typet type,
const bool  strict_formatting,
const unsigned long  radix_ul 
)

Get the numeric value of a character, assuming that the radix is large enough.

'+' and '-' yield 0.

Parameters
chrthe character to get the numeric value of
char_typethe type to use for characters
typethe type to use for the return value
strict_formattingif true, don't allow upper case characters
radix_ulthe radix, which should be between 2 and 36, or 0, in which case the return value will work for any radix
Returns
an integer expression of the given type with the numeric value of the char

There are four cases, which occur in ASCII in the following order: '+' and '-', digits, upper case letters, lower case letters

return char >= '0' ? (char - '0') : 0

return char >= 'a' ? (char - 'a' + 10) : char >= '0' ? (char - '0') : 0

return char >= 'a' ? (char - 'a' + 10) : char >= 'A' ? (char - 'A' + 10) : char >= '0' ? (char - '0') : 0

Definition at line 623 of file string_constraint_generator_valueof.cpp.

◆ get_return_code_type()

signedbv_typet get_return_code_type ( )

Definition at line 182 of file string_constraint_generator_main.cpp.

◆ is_digit_with_radix()

exprt is_digit_with_radix ( const exprt chr,
const bool  strict_formatting,
const exprt radix_as_char,
const unsigned long  radix_ul 
)

Check if a character is a digit with respect to the given radix, e.g.

if the radix is 10 then check if the character is in the range 0-9.

Parameters
chrthe character
strict_formattingif true, don't allow upper case characters
radix_as_charthe radix as an expression of the same type as chr
radix_ulthe radix, which should be between 2 and 36, or 0, in which case the return value will work for any radix
Returns
an expression for the condition

Definition at line 555 of file string_constraint_generator_valueof.cpp.

◆ is_positive()

exprt is_positive ( const exprt x)
Parameters
xan expression
Returns
a Boolean expression true exactly when x is positive

Definition at line 341 of file string_constraint_generator_main.cpp.

◆ length_constraint_for_concat()

exprt length_constraint_for_concat ( const array_string_exprt res,
const array_string_exprt s1,
const array_string_exprt s2,
array_poolt array_pool 
)

Add axioms enforcing that the length of res is that of the concatenation of s1 with s2

Definition at line 125 of file string_concatenation_builtin_function.cpp.

◆ length_constraint_for_concat_char()

exprt length_constraint_for_concat_char ( const array_string_exprt res,
const array_string_exprt s1,
array_poolt array_pool 
)

Add axioms enforcing that the length of res is that of the concatenation of s1 with.

Definition at line 140 of file string_concatenation_builtin_function.cpp.

◆ length_constraint_for_concat_substr()

exprt length_constraint_for_concat_substr ( const array_string_exprt res,
const array_string_exprt s1,
const array_string_exprt s2,
const exprt start,
const exprt end,
array_poolt array_pool 
)

Add axioms enforcing that the length of res is that of the concatenation of s1 with the substring of s2 starting at index ‘start’ and ending at indexend'‘.

Where start_index’ is max(0, start) and end' is max(min(end, s2.length), start')

Definition at line 102 of file string_concatenation_builtin_function.cpp.

◆ max_printed_string_length()

size_t max_printed_string_length ( const typet type,
unsigned long  radix_ul 
)

Calculate the string length needed to represent any value of the given type using the given radix.

Due to floating point rounding errors we sometimes return a value 1 larger than needed, which is fine for our purposes.

Parameters
typethe type that we are considering values of
radix_ulthe radix we are using, or 0, in which case the return value will work for any radix
Returns
the maximum string length

We want to calculate max, the maximum number of characters needed to represent any value of the given type.

For signed types, the longest string will be for -2^(n_bits-1), so max = 1 + min{k: 2^(n_bits-1) < radix^k} (the 1 is for the minus sign) = 1 + min{k: n_bits-1 < k log_2(radix)} = 1 + min{k: k > (n_bits-1) / log_2(radix)} = 1 + min{k: k > floor((n_bits-1) / log_2(radix))} = 1 + (1 + floor((n_bits-1) / log_2(radix))) = 2 + floor((n_bits-1) / log_2(radix))

For unsigned types, the longest string will be for (2^n_bits)-1, so max = min{k: (2^n_bits)-1 < radix^k} = min{k: 2^n_bits <= radix^k} = min{k: n_bits <= k log_2(radix)} = min{k: k >= n_bits / log_2(radix)} = min{k: k >= ceil(n_bits / log_2(radix))} = ceil(n_bits / log_2(radix))

Definition at line 697 of file string_constraint_generator_valueof.cpp.

◆ maximum()

exprt maximum ( const exprt a,
const exprt b 
)
Returns
expression representing the maximum of two expressions

Definition at line 404 of file string_constraint_generator_main.cpp.

◆ merge()

void merge ( string_constraintst result,
string_constraintst  other 
)

Merge two sets of constraints by appending to the first one.

Definition at line 101 of file string_constraint_generator_main.cpp.

◆ minimum()

exprt minimum ( const exprt a,
const exprt b 
)
Returns
expression representing the minimum of two expressions

Definition at line 399 of file string_constraint_generator_main.cpp.

◆ sum_overflows()

exprt sum_overflows ( const plus_exprt sum)
Returns
Boolean true when the sum of the two expressions overflows

Definition at line 40 of file string_constraint_generator_main.cpp.

◆ zero_if_negative()

exprt zero_if_negative ( const exprt expr)

Returns a non-negative version of the argument.

Parameters
exprexpression of which we want a non-negative version
Returns
max(0, expr)

Definition at line 412 of file string_constraint_generator_main.cpp.