xfygogo/exprtk
1
0
Fork 0
mirror of https://github.com/ArashPartow/exprtk.git synced 2025-06-22 16:28:57 +00:00
Code Issues Packages Projects Releases Wiki Activity

C++ Mathematical Expression Library (ExprTk) https://www.partow.net/programming/exprtk/index.html

Browse Source
This commit is contained in:
ArashPartow
2023-01-01 02:18:35 +00:00
parent 806c519c91
commit f46bffcd69
26 changed files with 1235 additions and 787 deletions
Download Patch File Download Diff File Expand all files Collapse all files

166
readme.txt
View File

@ -115,7 +115,7 @@ Free use of the C++ Mathematical Expression Toolkit Library is
permitted under the guidelines and in accordance with the most current
version of the MIT License.
http://www.opensource.org/licenses/MIT
https://www.opensource.org/licenses/MIT
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@ -707,7 +707,7 @@ the expression instance and to also allow the expression to be
evaluated using the current value of the element.
Note: Any variable reference provided to a given symbol_table
instance, must have a life time at least as long as the life-time of
instance, must have a life-time at least as long as the life-time of
the symbol_table instance. In the event the variable reference is
invalidated before the symbol_table or any dependent expression
instances have been destructed, then any associated expression
@ -868,6 +868,66 @@ a false result due to one or more of the following reasons:
6. The symbol_table instance is in an invalid state
A further property of symbol tables is that they can be classified at
instantiation as either being mutable (by default) or immutable. The
following demonstrates construction of an immutable symbol table
instance:
symbol_table_t immutable_symbol_table
(symbol_table_t::symtab_mutability_type::e_immutable);
When a symbol table, that has been constructed as being immutable, is
registered with an expression, any statements in the expression string
that modify the variables that are managed by the immutable symbol
table will result in a compilation error. The operations that trigger
the mutability constraint are the following assignment operators:
1. Assignment: :=
2. Assign operation: +=, -=, *=, /= , %=
The main reason for this functionality is that, one may want the
immutability properties that come with constness of a variable such as
scalars, vectors and strings, but not necessarily the accompanying
compile time const-folding optimisations, that would result in the
value of the variables being retrieved only once at compile time,
causing external updates to the variables to not be part of the
expression evaluation.
symbol_table_t immutable_symbol_table
(symbol_table_t::symtab_mutability_type::e_immutable);
T x = 0.0;
const std::string expression_str = "x + (y + y)";
immutable_symbol_table.add_variable("x" , x );
immutable_symbol_table.add_constant("y" , 123.0);
expression_t expression;
expression.register_symbol_table(immutabile_symbol_table);
parser_t parser;
parser.compile(expression_str, expression)
for (; x < 10.0; ++x)
{
const auto expected_value = x + (123.0 + 123.0);
const auto result_value = expression.value();
assert(expression.value() != expected_value);
}
In the above example, there are two variables X and Y. Where Y is a
constant and X is a normal variable. Both are registered with a symbol
table that is immutable. The expression when compiled will result in
the "(y + y)" part being const-folded at compile time to the literal
value of 246. Whereas the current value of X, being updated via the
for-loop, externally to the expression and the symbol table will be
available to the expression upon each evaluation.
(2) Expression
A structure that holds an Abstract Syntax Tree or AST for a specified
expression and is used to evaluate said expression. Evaluation of the
@ -1020,7 +1080,7 @@ may include user defined variables or functions. These are embedded as
references into the expression's AST. When copying an expression, said
references need to also be copied. If the references are blindly
copied, it will then result in two or more identical expressions
utilizing the exact same references for variables. This obviously is
utilising the exact same references for variables. This obviously is
not the default assumed scenario and will give rise to non-obvious
behaviours when using the expressions in various contexts such as
multi-threading et al.
@ -1110,6 +1170,7 @@ enabled by default. The options and their explanations are as follows:
(5) Sequence Check
(6) Commutative Check
(7) Strength Reduction Check
(8) Stack And Node Depth Check
(1) Replacer (e_replacer)
@ -1218,6 +1279,43 @@ desired over the strength reduced form. In these situations it is best
to turn off strength reduction optimisations or to use a type with a
larger numerical bound.
(8) Stack And Node Depth Check
ExprTk incorporates a recursive descent parser. When parsing
expressions comprising inner sub-expressions, the recursive nature of
the parsing process causes the stack to grow. If the expression causes
the stack to grow beyond the stack size limit, this would lead to a
stackoverflow and its associated stack corruption and security
vulnerability issues.
Similarly to parsing, evaluating an expression may cause the stack to
grow. Such things like user defined functions, composite functions and
the general nature of the AST being evaluated can cause the stack to
grow, and may result in potential stackoverflow issues as denoted
above.
ExprTk provides a set of checks that prevent both of the above denoted
problems at compile time. These check rely on two specific limits
being set on the parser instance, these limits are:
1. max_stack_depth (default: 400)
2. max_node_depth (default: 10000)
The following demonstrates how these two parser parameters can be set:
parser_t parser;
parser.set_max_stack_depth(100);
parser.set_max_node_depth(200);
In the above code, during parsing if the stack depth reaches or
exceeds 100 levels, the parsing process will immediately halt and
return with a failure. Similarly, during synthesizing the AST nodes,
if the compilation process detects an AST tree depth exceeding 200
levels the parsing process will halt and return a parsing failure.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 12 - EXPRESSION STRUCTURES]
@ -1780,7 +1878,7 @@ value is not a vector but rather a single value.
sum(x > 0 and x < 5) == x[]
When utilizing external user defined vectors via the symbol table as
When utilising external user defined vectors via the symbol table as
opposed to expression local defined vectors, the typical 'add_vector'
method from the symbol table will register the entirety of the vector
that is passed. The following example attempts to evaluate the sum of
@ -3489,7 +3587,7 @@ ExprTk reserved words, the add_function call will fail.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 20 - EXPRESSION RETURN VALUES]
ExprTk expressions can return immediately from any point by utilizing
ExprTk expressions can return immediately from any point by utilising
the return call. Furthermore the return call can be used to transfer
out multiple return values from within the expression.
@ -4591,52 +4689,58 @@ part of a compiler command line switch or scoped around the include to
the ExprTk header. The defines are as follows:
(01) exprtk_enable_debugging
(02) exprtk_disable_comments
(03) exprtk_disable_break_continue
(04) exprtk_disable_sc_andor
(05) exprtk_disable_return_statement
(06) exprtk_disable_enhanced_features
(07) exprtk_disable_string_capabilities
(08) exprtk_disable_superscalar_unroll
(09) exprtk_disable_rtl_io_file
(10) exprtk_disable_rtl_vecops
(11) exprtk_disable_caseinsensitivity
(02) exprtk_disable_cardinal_pow_optimisation
(03) exprtk_disable_comments
(04) exprtk_disable_break_continue
(05) exprtk_disable_sc_andor
(06) exprtk_disable_return_statement
(07) exprtk_disable_enhanced_features
(08) exprtk_disable_string_capabilities
(09) exprtk_disable_superscalar_unroll
(10) exprtk_disable_rtl_io
(11) exprtk_disable_rtl_io_file
(12) exprtk_disable_rtl_vecops
(13) exprtk_disable_caseinsensitivity
(14) exprtk_enable_range_runtime_checks
(01) exprtk_enable_debugging
This define will enable printing of debug information to stdout during
the compilation process.
(02) exprtk_disable_comments
(02) exprtk_disable_cardinal_pow_optimisation
This define will disable the optimisation invoked when constant
integers are used as powers in exponentiation expressions (eg: x^7).
(03) exprtk_disable_comments
This define will disable the ability for expressions to have comments.
Expressions that have comments when parsed with a build that has this
option, will result in a compilation failure.
(03) exprtk_disable_break_continue
(04) exprtk_disable_break_continue
This define will disable the loop-wise 'break' and 'continue'
capabilities. Any expression that contains those keywords will result
in a compilation failure.
(04) exprtk_disable_sc_andor
(05) exprtk_disable_sc_andor
This define will disable the short-circuit '&' (and) and '|' (or)
operators
(05) exprtk_disable_return_statement
(06) exprtk_disable_return_statement
This define will disable use of return statements within expressions.
(06) exprtk_disable_enhanced_features
(07) exprtk_disable_enhanced_features
This define will disable all enhanced features such as strength
reduction and special function optimisations and expression specific
type instantiations. This feature will reduce compilation times and
binary sizes but will also result in massive performance degradation
of expression evaluations.
(07) exprtk_disable_string_capabilities
(08) exprtk_disable_string_capabilities
This define will disable all string processing capabilities. Any
expression that contains a string or string related syntax will result
in a compilation failure.
(08) exprtk_disable_superscalar_unroll
(09) exprtk_disable_superscalar_unroll
This define will set the loop unroll batch size to 4 operations per
loop instead of the default 8 operations. This define is used in
operations that involve vectors and aggregations over vectors. When
@ -4644,22 +4748,32 @@ targeting non-superscalar architectures, it may be recommended to
build using this particular option if efficiency of evaluations is of
concern.
(09) exprtk_disable_rtl_io_file
(10) exprtk_disable_rtl_io
This define will disable all of basic IO RTL package features. When
present, any attempt to register the basic IO RTL package with a given
symbol table will fail causing a compilation error.
(11) exprtk_disable_rtl_io_file
This define will disable the file I/O RTL package features. When
present, any attempts to register the file I/O package with a given
symbol table will fail causing a compilation error.
(10) exprtk_disable_rtl_vecops
(12) exprtk_disable_rtl_vecops
This define will disable the extended vector operations RTL package
features. When present, any attempts to register the vector operations
package with a given symbol table will fail causing a compilation
error.
(11) exprtk_disable_caseinsensitivity
(13) exprtk_disable_caseinsensitivity
This define will disable case-insensitivity when matching variables
and functions. Furthermore all reserved and keywords will only be
acknowledged when in all lower-case.
(14) exprtk_enable_range_runtime_checks
This define will enable run-time checks pertaining to vector indexing
operations used in any of the vector-to-vector and vector-to-scalar
operations.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[SECTION 28 - FILES]