contrib/visupng/cexcept.h - third_party/libpng - Git at Google

 /*===
 cexcept.h 2.0.1 (2008-Jul-19-Sat)
 http://www.nicemice.net/cexcept/
 Adam M. Costello
 http://www.nicemice.net/amc/

 An interface for exception-handling in ANSI C (C89 and subsequent ISO
 standards), developed jointly with Cosmin Truta.

     Copyright (c) 2000-2008 Adam M. Costello and Cosmin Truta.
     This software may be modified only if its author and version
     information is updated accurately, and may be redistributed
     only if accompanied by this unaltered notice.  Subject to those
     restrictions, permission is granted to anyone to do anything
     with this software.  The copyright holders make no guarantees
     regarding this software, and are not responsible for any damage
     resulting from its use.

 The cexcept interface is not compatible with and cannot interact
 with system exceptions (like division by zero or memory segmentation
 violation), compiler-generated exceptions (like C++ exceptions), or
 other exception-handling interfaces.

 When using this interface across multiple .c files, do not include
 this header file directly.  Instead, create a wrapper header file that
 includes this header file and then invokes the define_exception_type
 macro (see below).  The .c files should then include that header file.

 The interface consists of one type, one well-known name, and six macros.


 define_exception_type(type_name);

     This macro is used like an external declaration.  It specifies
     the type of object that gets copied from the exception thrower to
     the exception catcher.  The type_name can be any type that can be
     assigned to, that is, a non-constant arithmetic type, struct, union,
     or pointer.  Examples:

         define_exception_type(int);

         enum exception { out_of_memory, bad_arguments, disk_full };
         define_exception_type(enum exception);

         struct exception { int code; const char *msg; };
         define_exception_type(struct exception);

     Because throwing an exception causes the object to be copied (not
     just once, but twice), programmers may wish to consider size when
     choosing the exception type.


 struct exception_context;

     This type may be used after the define_exception_type() macro has
     been invoked.  A struct exception_context must be known to both
     the thrower and the catcher.  It is expected that there be one
     context for each thread that uses exceptions.  It would certainly
     be dangerous for multiple threads to access the same context.
     One thread can use multiple contexts, but that is likely to be
     confusing and not typically useful.  The application can allocate
     this structure in any way it pleases--automatic, static, or dynamic.
     The application programmer should pretend not to know the structure
     members, which are subject to change.


 struct exception_context *the_exception_context;

     The Try/Catch and Throw statements (described below) implicitly
     refer to a context, using the name the_exception_context.  It is
     the application's responsibility to make sure that this name yields
     the address of a mutable (non-constant) struct exception_context
     wherever those statements are used.  Subject to that constraint, the
     application may declare a variable of this name anywhere it likes
     (inside a function, in a parameter list, or externally), and may
     use whatever storage class specifiers (static, extern, etc) or type
     qualifiers (const, volatile, etc) it likes.  Examples:

         static struct exception_context
           * const the_exception_context = &foo;

         { struct exception_context *the_exception_context = bar; ... }

         int blah(struct exception_context *the_exception_context, ...);

         extern struct exception_context the_exception_context[1];

     The last example illustrates a trick that avoids creating a pointer
     object separate from the structure object.

     The name could even be a macro, for example:

         struct exception_context ec_array[numthreads];
         #define the_exception_context (ec_array + thread_id)

     Be aware that the_exception_context is used several times by the
     Try/Catch/Throw macros, so it shouldn't be expensive or have side
     effects.  The expansion must be a drop-in replacement for an
     identifier, so it's safest to put parentheses around it.


 void init_exception_context(struct exception_context *ec);

     For context structures allocated statically (by an external
     definition or using the "static" keyword), the implicit
     initialization to all zeros is sufficient, but contexts allocated
     by other means must be initialized using this macro before they
     are used by a Try/Catch statement.  It does no harm to initialize
     a context more than once (by using this macro on a statically
     allocated context, or using this macro twice on the same context),
     but a context must not be re-initialized after it has been used by a
     Try/Catch statement.


 Try statement
 Catch (expression) statement

     The Try/Catch/Throw macros are capitalized in order to avoid
     confusion with the C++ keywords, which have subtly different
     semantics.

     A Try/Catch statement has a syntax similar to an if/else statement,
     except that the parenthesized expression goes after the second
     keyword rather than the first.  As with if/else, there are two
     clauses, each of which may be a simple statement ending with a
     semicolon or a brace-enclosed compound statement.  But whereas
     the else clause is optional, the Catch clause is required.  The
     expression must be a modifiable lvalue (something capable of being
     assigned to) of the same type (disregarding type qualifiers) that
     was passed to define_exception_type().

     If a Throw that uses the same exception context as the Try/Catch is
     executed within the Try clause (typically within a function called
     by the Try clause), and the exception is not caught by a nested
     Try/Catch statement, then a copy of the exception will be assigned
     to the expression, and control will jump to the Catch clause.  If no
     such Throw is executed, then the assignment is not performed, and
     the Catch clause is not executed.

     The expression is not evaluated unless and until the exception is
     caught, which is significant if it has side effects, for example:

         Try foo();
         Catch (p[++i].e) { ... }

     IMPORTANT: Jumping into or out of a Try clause (for example via
     return, break, continue, goto, longjmp) is forbidden--the compiler
     will not complain, but bad things will happen at run-time.  Jumping
     into or out of a Catch clause is okay, and so is jumping around
     inside a Try clause.  In many cases where one is tempted to return
     from a Try clause, it will suffice to use Throw, and then return
     from the Catch clause.  Another option is to set a flag variable and
     use goto to jump to the end of the Try clause, then check the flag
     after the Try/Catch statement.

     IMPORTANT: The values of any non-volatile automatic variables
     changed within the Try clause are undefined after an exception is
     caught.  Therefore, variables modified inside the Try block whose
     values are needed later outside the Try block must either use static
     storage or be declared with the "volatile" type qualifier.


 Throw expression;

     A Throw statement is very much like a return statement, except that
     the expression is required.  Whereas return jumps back to the place
     where the current function was called, Throw jumps back to the Catch
     clause of the innermost enclosing Try clause.  The expression must
     be compatible with the type passed to define_exception_type().  The
     exception must be caught, otherwise the program may crash.

     Slight limitation:  If the expression is a comma-expression, it must
     be enclosed in parentheses.


 Try statement
 Catch_anonymous statement

     When the value of the exception is not needed, a Try/Catch statement
     can use Catch_anonymous instead of Catch (expression).


 Everything below this point is for the benefit of the compiler.  The
 application programmer should pretend not to know any of it, because it
 is subject to change.

 ===*/


 #ifndef CEXCEPT_H
 #define CEXCEPT_H


 #include <setjmp.h>

 #define define_exception_type(etype) \
 struct exception_context { \
   jmp_buf *penv; \
   int caught; \
   volatile struct { etype etmp; } v; \
 }

 /* etmp must be volatile because the application might use automatic */
 /* storage for the_exception_context, and etmp is modified between   */
 /* the calls to setjmp() and longjmp().  A wrapper struct is used to */
 /* avoid warnings about a duplicate volatile qualifier in case etype */
 /* already includes it.                                              */

 #define init_exception_context(ec) ((void)((ec)->penv = 0))

 #define Try \
   { \
     jmp_buf *exception__prev, exception__env; \
     exception__prev = the_exception_context->penv; \
     the_exception_context->penv = &exception__env; \
     if (setjmp(exception__env) == 0) { \
       do

 #define exception__catch(action) \
       while (the_exception_context->caught = 0, \
              the_exception_context->caught); \
     } \
     else { \
       the_exception_context->caught = 1; \
     } \
     the_exception_context->penv = exception__prev; \
   } \
   if (!the_exception_context->caught || action) { } \
   else

 #define Catch(e) exception__catch(((e) = the_exception_context->v.etmp, 0))
 #define Catch_anonymous exception__catch(0)

 /* Try ends with do, and Catch begins with while(0) and ends with     */
 /* else, to ensure that Try/Catch syntax is similar to if/else        */
 /* syntax.                                                            */
 /*                                                                    */
 /* The 0 in while(0) is expressed as x=0,x in order to appease        */
 /* compilers that warn about constant expressions inside while().     */
 /* Most compilers should still recognize that the condition is always */
 /* false and avoid generating code for it.                            */

 #define Throw \
   for (;; longjmp(*the_exception_context->penv, 1)) \
     the_exception_context->v.etmp =


 #endif /* CEXCEPT_H */
	/*===
	cexcept.h 2.0.1 (2008-Jul-19-Sat)
	http://www.nicemice.net/cexcept/
	Adam M. Costello
	http://www.nicemice.net/amc/

	An interface for exception-handling in ANSI C (C89 and subsequent ISO
	standards), developed jointly with Cosmin Truta.

	Copyright (c) 2000-2008 Adam M. Costello and Cosmin Truta.
	This software may be modified only if its author and version
	information is updated accurately, and may be redistributed
	only if accompanied by this unaltered notice. Subject to those
	restrictions, permission is granted to anyone to do anything
	with this software. The copyright holders make no guarantees
	regarding this software, and are not responsible for any damage
	resulting from its use.

	The cexcept interface is not compatible with and cannot interact
	with system exceptions (like division by zero or memory segmentation
	violation), compiler-generated exceptions (like C++ exceptions), or
	other exception-handling interfaces.

	When using this interface across multiple .c files, do not include
	this header file directly. Instead, create a wrapper header file that
	includes this header file and then invokes the define_exception_type
	macro (see below). The .c files should then include that header file.

	The interface consists of one type, one well-known name, and six macros.


	define_exception_type(type_name);

	This macro is used like an external declaration. It specifies
	the type of object that gets copied from the exception thrower to
	the exception catcher. The type_name can be any type that can be
	assigned to, that is, a non-constant arithmetic type, struct, union,
	or pointer. Examples:

	define_exception_type(int);

	enum exception { out_of_memory, bad_arguments, disk_full };
	define_exception_type(enum exception);

	struct exception { int code; const char *msg; };
	define_exception_type(struct exception);

	Because throwing an exception causes the object to be copied (not
	just once, but twice), programmers may wish to consider size when
	choosing the exception type.


	struct exception_context;

	This type may be used after the define_exception_type() macro has
	been invoked. A struct exception_context must be known to both
	the thrower and the catcher. It is expected that there be one
	context for each thread that uses exceptions. It would certainly
	be dangerous for multiple threads to access the same context.
	One thread can use multiple contexts, but that is likely to be
	confusing and not typically useful. The application can allocate
	this structure in any way it pleases--automatic, static, or dynamic.
	The application programmer should pretend not to know the structure
	members, which are subject to change.


	struct exception_context *the_exception_context;

	The Try/Catch and Throw statements (described below) implicitly
	refer to a context, using the name the_exception_context. It is
	the application's responsibility to make sure that this name yields
	the address of a mutable (non-constant) struct exception_context
	wherever those statements are used. Subject to that constraint, the
	application may declare a variable of this name anywhere it likes
	(inside a function, in a parameter list, or externally), and may
	use whatever storage class specifiers (static, extern, etc) or type
	qualifiers (const, volatile, etc) it likes. Examples:

	static struct exception_context
	* const the_exception_context = &foo;

	{ struct exception_context *the_exception_context = bar; ... }

	int blah(struct exception_context *the_exception_context, ...);

	extern struct exception_context the_exception_context[1];

	The last example illustrates a trick that avoids creating a pointer
	object separate from the structure object.

	The name could even be a macro, for example:

	struct exception_context ec_array[numthreads];
	#define the_exception_context (ec_array + thread_id)

	Be aware that the_exception_context is used several times by the
	Try/Catch/Throw macros, so it shouldn't be expensive or have side
	effects. The expansion must be a drop-in replacement for an
	identifier, so it's safest to put parentheses around it.


	void init_exception_context(struct exception_context *ec);

	For context structures allocated statically (by an external
	definition or using the "static" keyword), the implicit
	initialization to all zeros is sufficient, but contexts allocated
	by other means must be initialized using this macro before they
	are used by a Try/Catch statement. It does no harm to initialize
	a context more than once (by using this macro on a statically
	allocated context, or using this macro twice on the same context),
	but a context must not be re-initialized after it has been used by a
	Try/Catch statement.


	Try statement
	Catch (expression) statement

	The Try/Catch/Throw macros are capitalized in order to avoid
	confusion with the C++ keywords, which have subtly different
	semantics.

	A Try/Catch statement has a syntax similar to an if/else statement,
	except that the parenthesized expression goes after the second
	keyword rather than the first. As with if/else, there are two
	clauses, each of which may be a simple statement ending with a
	semicolon or a brace-enclosed compound statement. But whereas
	the else clause is optional, the Catch clause is required. The
	expression must be a modifiable lvalue (something capable of being
	assigned to) of the same type (disregarding type qualifiers) that
	was passed to define_exception_type().

	If a Throw that uses the same exception context as the Try/Catch is
	executed within the Try clause (typically within a function called
	by the Try clause), and the exception is not caught by a nested
	Try/Catch statement, then a copy of the exception will be assigned
	to the expression, and control will jump to the Catch clause. If no
	such Throw is executed, then the assignment is not performed, and
	the Catch clause is not executed.

	The expression is not evaluated unless and until the exception is
	caught, which is significant if it has side effects, for example:

	Try foo();
	Catch (p[++i].e) { ... }

	IMPORTANT: Jumping into or out of a Try clause (for example via
	return, break, continue, goto, longjmp) is forbidden--the compiler
	will not complain, but bad things will happen at run-time. Jumping
	into or out of a Catch clause is okay, and so is jumping around
	inside a Try clause. In many cases where one is tempted to return
	from a Try clause, it will suffice to use Throw, and then return
	from the Catch clause. Another option is to set a flag variable and
	use goto to jump to the end of the Try clause, then check the flag
	after the Try/Catch statement.

	IMPORTANT: The values of any non-volatile automatic variables
	changed within the Try clause are undefined after an exception is
	caught. Therefore, variables modified inside the Try block whose
	values are needed later outside the Try block must either use static
	storage or be declared with the "volatile" type qualifier.


	Throw expression;

	A Throw statement is very much like a return statement, except that
	the expression is required. Whereas return jumps back to the place
	where the current function was called, Throw jumps back to the Catch
	clause of the innermost enclosing Try clause. The expression must
	be compatible with the type passed to define_exception_type(). The
	exception must be caught, otherwise the program may crash.

	Slight limitation: If the expression is a comma-expression, it must
	be enclosed in parentheses.


	Try statement
	Catch_anonymous statement

	When the value of the exception is not needed, a Try/Catch statement
	can use Catch_anonymous instead of Catch (expression).


	Everything below this point is for the benefit of the compiler. The
	application programmer should pretend not to know any of it, because it
	is subject to change.

	===*/


	#ifndef CEXCEPT_H
	#define CEXCEPT_H


	#include <setjmp.h>

	#define define_exception_type(etype) \
	struct exception_context { \
	jmp_buf *penv; \
	int caught; \
	volatile struct { etype etmp; } v; \
	}

	/* etmp must be volatile because the application might use automatic */
	/* storage for the_exception_context, and etmp is modified between */
	/* the calls to setjmp() and longjmp(). A wrapper struct is used to */
	/* avoid warnings about a duplicate volatile qualifier in case etype */
	/* already includes it. */

	#define init_exception_context(ec) ((void)((ec)->penv = 0))

	#define Try \
	{ \
	jmp_buf *exception__prev, exception__env; \
	exception__prev = the_exception_context->penv; \
	the_exception_context->penv = &exception__env; \
	if (setjmp(exception__env) == 0) { \
	do

	#define exception__catch(action) \
	while (the_exception_context->caught = 0, \
	the_exception_context->caught); \
	} \
	else { \
	the_exception_context->caught = 1; \
	} \
	the_exception_context->penv = exception__prev; \
	} \
	if (!the_exception_context->caught \|\| action) { } \
	else

	#define Catch(e) exception__catch(((e) = the_exception_context->v.etmp, 0))
	#define Catch_anonymous exception__catch(0)

	/* Try ends with do, and Catch begins with while(0) and ends with */
	/* else, to ensure that Try/Catch syntax is similar to if/else */
	/* syntax. */
	/* */
	/* The 0 in while(0) is expressed as x=0,x in order to appease */
	/* compilers that warn about constant expressions inside while(). */
	/* Most compilers should still recognize that the condition is always */
	/* false and avoid generating code for it. */

	#define Throw \
	for (;; longjmp(*the_exception_context->penv, 1)) \
	the_exception_context->v.etmp =


	#endif /* CEXCEPT_H */