@@@ better tests

[mLib] / utils / control.h

/* -*-c-*-
 *
 * Control operators, after Simon Tatham
 *
 * (c) 2022 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Library General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 *
 * mLib is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with mLib.  If not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
 * USA.
 */

#ifndef MLIB_CONTROL_H
#define MLIB_CONTROL_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

#ifndef MLIB_MACROS_H
#  include "macros.h"
#endif

/*----- Macros provided ---------------------------------------------------*/

/* @MCTRL__LABEL(tag)@ *
 *
 * Expand to a plausibly unique label based on the current line number and
 * the @tag@.
 */
#define MCTRL__LABEL(tag) GLUE(_mctrl__##tag##__, __LINE__)

/* @FIRSTBRANCH(tag_0) stmt_0@
 * [@MIDBRANCH(tag_i) stmt_i ...@]
 * @LASTBRANCH(tag_n) stmt_n@
 * @GOBRANCH(tag);@
 *
 * If control enters at the top, then only <stmt_0> is executed, followed by
 * the statement after.  Following @GOBRANCH(tag)@, control continues
 * from the correspondingly tagged statement, and continues with the
 * following statement again.
 */
#define FIRSTBRANCH(tag)  if (1) { goto MCTRL__LABEL(tag); MCTRL__LABEL(tag):
#define MIDBRANCH(tag)    } else if (0) MCTRL__LABEL(tag): {
#define LASTBRANCH(tag)   } else MCTRL__LABEL(tag):
#define GOBRANCH(tag)     goto MCTRL__LABEL(tag)

/* @BEFORE(tag, stmt_0) stmt_1@
 *
 * Execute @stmt_0@ and then @stmt_1@.
 */
#define BEFORE(tag, stmt)						\
	if (1) { stmt goto MCTRL__LABEL(tag##__before_body); }		\
	else MCTRL__LABEL(tag##__before_body):

/* @AFTER(tag, stmt_0) stmt_1@
 *
 * Execute @stmt_1@ and then @stmt_0@.  If either statement invokes @break@
 * then control immediately transfers to the statement following @AFTER@.  If
 * either invokes @continue@, then control returns to @stmt_0@.
 */
#define AFTER(tag, stmt)						\
	if (1) goto MCTRL__LABEL(tag##__after_body);			\
	else if (1) { MCTRL__LABEL(tag##__after_end): stmt }		\
	else for (;;)							\
	  if (1) goto MCTRL__LABEL(tag##__after_end);			\
	  else MCTRL__LABEL(tag##__after_body):

/* @WRAP(tag, before, onend, onbreak) stmt@
 *
 * Execute the @before@ statement, followed by @stmt@.  If @stmt@ invokes
 * @break@, then @onbreak@ is immediately executed; if @stmt@ completes
 * normally, or invokes @continue@ then @onend@ is immediately executed.
 * Any @break@ and @continue@ in the @before@, @onend@, and @onbreak@
 * statements behave as one would expect from their context.
 */
#define WRAP(tag, before, onend, onbreak)				\
	if (1) { before goto MCTRL__LABEL(tag##__wrap_body); }		\
	else if (1) { MCTRL__LABEL(tag##__wrap_end): onend }		\
	else if (1) { MCTRL__LABEL(tag##__wrap_break): onbreak }	\
	else for (;;)							\
	  if (1) goto MCTRL__LABEL(tag##__wrap_break);			\
	  else for (;;)							\
	    if (1) goto MCTRL__LABEL(tag##__wrap_end);			\
	    else MCTRL__LABEL(tag##__wrap_body):

/* @ALLOWELSE(tag, before, onend, onbreak) stmt_0 [else stmt_1]@
 * @GOELSE(tag);@
 *
 * Execute the @before@ statement, followed by @stmt_0@.  If @stmt_0@
 * completes, or invokes @break@ or @continue@, then control continues with
 * the next statement.  If @GOELSE(tag)@ is invoked anywhere in the
 * function, then @before@ is executed, followed by @stmt_1@ (if present).
 * If @stmt_1@ invokes @break@ then control passes to @onbreak@; if @stmt_1@
 * ends normally then control passes to @onend@.  Any @break@ and @continue@
 * in the @before@, @onend@, and @onbreak@ statements behave as one would
 * expect from their context.
 */
#define ALLOWELSE(tag, before, onend, onbreak)				\
	if (1) goto MCTRL__LABEL(tag##__allowelse_body);		\
	else if (1) MCTRL__LABEL(tag##__allowelse_body_end): ;		\
	else if (1) { MCTRL__LABEL(tag##__allowelse_else_end): onend }	\
	else if (1) { MCTRL__LABEL(tag##__allowelse_else_break): onbreak } \
	else if (1) {							\
	MCTRL__LABEL(tag##__allowelse_before_else):			\
	  before goto MCTRL__LABEL(tag##__allowelse_else);		\
	} else for (;;)							\
	  if (1) goto MCTRL__LABEL(tag##__allowelse_else_break);	\
	  else for (;;)							\
	    if (1) goto MCTRL__LABEL(tag##__allowelse_else_end);	\
	    else MCTRL__LABEL(tag##__allowelse_else): if (0) for (;;)	\
	      if (1) goto MCTRL__LABEL(tag##__allowelse_body_end);	\
	      else MCTRL__LABEL(tag##__allowelse_body):
#define GOELSE(tag)							\
	goto MCTRL__LABEL(tag##__allowelse_before_else)

/* @DOWHILE(tag, cond) stmt@
 *
 * Repeatedly execute @stmt@ until @cond@ evaluates to zero.  Execute @stmt@
 * at least once.  The @break@ and @continue@ statements work within @stmt@
 * as one would expect.
 */
#define DOWHILE(tag, cond)						\
	if (1) goto MCTRL__LABEL(tag##__dowhile_body);			\
	else while (cond) MCTRL__LABEL(tag##__dowhile_body):

/* @DECL(tag, decl) stmt@
 *
 * Execute @stmt@ with @decl@ in scope.  If @stmt@ completes or invokes
 * @break@ or @continue@ then control continues with the statement following
 * @DECL@.  Internally, this uses @for@, so it only works in C99 or later, or
 * C++.
 */
#if __STDC_VERSION__ >= 199901 || defined(__cplusplus)
#  define DECL(tag, decl)						\
	for (decl;;)							\
	  if (1) goto MCTRL__LABEL(tag##__decl_body);			\
	  else if (1) MCTRL__LABEL(tag##__decl_exit): break;		\
	  else for (;;)							\
	    if (1) goto MCTRL__LABEL(tag##__decl_exit);			\
	    else MCTRL__LABEL(tag##__decl_body):
#endif

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif