mdw@git.distorted.org.uk Git - mLib/blob - utils/control.h

   1 /* -*-c-*-
   2  *
   3  * Control operators, after Simon Tatham
   4  *
   5  * (c) 2022 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of the mLib utilities library.
  11  *
  12  * mLib is free software: you can redistribute it and/or modify it under
  13  * the terms of the GNU Library General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or (at
  15  * your option) any later version.
  16  *
  17  * mLib is distributed in the hope that it will be useful, but WITHOUT
  18  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
  20  * License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with mLib.  If not, write to the Free Software
  24  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  25  * USA.
  26  */
  27
  28 #ifndef MLIB_CONTROL_H
  29 #define MLIB_CONTROL_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #ifndef MLIB_MACROS_H
  38 #  include "macros.h"
  39 #endif
  40
  41 /*----- Macros provided ---------------------------------------------------*/
  42
  43 /* @MCTRL__LABEL(tag)@ *
  44  *
  45  * Expand to a plausibly unique label based on the current line number and
  46  * the @tag@.
  47  */
  48 #define MCTRL__LABEL(tag) GLUE(_mctrl__##tag##__, __LINE__)
  49
  50 /* @FIRSTBRANCH(tag_0) stmt_0@
  51  * [@MIDBRANCH(tag_i) stmt_i ...@]
  52  * @LASTBRANCH(tag_n) stmt_n@
  53  * @GOBRANCH(tag);@
  54  *
  55  * If control enters at the top, then only <stmt_0> is executed, followed by
  56  * the statement after.  Following @GOBRANCH(tag)@, control continues
  57  * from the correspondingly tagged statement, and continues with the
  58  * following statement again.
  59  */
  60 #define FIRSTBRANCH(tag)  if (1) { goto MCTRL__LABEL(tag); MCTRL__LABEL(tag):
  61 #define MIDBRANCH(tag)    } else if (0) MCTRL__LABEL(tag): {
  62 #define LASTBRANCH(tag)   } else MCTRL__LABEL(tag):
  63 #define GOBRANCH(tag)     goto MCTRL__LABEL(tag)
  64
  65 /* @BEFORE(tag, stmt_0) stmt_1@
  66  *
  67  * Execute @stmt_0@ and then @stmt_1@.
  68  */
  69 #define BEFORE(tag, stmt)                                               \
  70         if (1) { stmt goto MCTRL__LABEL(tag##__before_body); }          \
  71         else MCTRL__LABEL(tag##__before_body):
  72
  73 /* @AFTER(tag, stmt_0) stmt_1@
  74  *
  75  * Execute @stmt_1@ and then @stmt_0@.  If either statement invokes @break@
  76  * then control immediately transfers to the statement following @AFTER@.  If
  77  * either invokes @continue@, then control returns to @stmt_0@.
  78  */
  79 #define AFTER(tag, stmt)                                                \
  80         if (1) goto MCTRL__LABEL(tag##__after_body);                    \
  81         else if (1) { MCTRL__LABEL(tag##__after_end): stmt }            \
  82         else for (;;)                                                   \
  83           if (1) goto MCTRL__LABEL(tag##__after_end);                   \
  84           else MCTRL__LABEL(tag##__after_body):
  85
  86 /* @WRAP(tag, before, onend, onbreak) stmt@
  87  *
  88  * Execute the @before@ statement, followed by @stmt@.  If @stmt@ invokes
  89  * @break@, then @onbreak@ is immediately executed; if @stmt@ completes
  90  * normally, or invokes @continue@ then @onend@ is immediately executed.
  91  * Any @break@ and @continue@ in the @before@, @onend@, and @onbreak@
  92  * statements behave as one would expect from their context.
  93  */
  94 #define WRAP(tag, before, onend, onbreak)                               \
  95         if (1) { before goto MCTRL__LABEL(tag##__wrap_body); }          \
  96         else if (1) { MCTRL__LABEL(tag##__wrap_end): onend }            \
  97         else if (1) { MCTRL__LABEL(tag##__wrap_break): onbreak }        \
  98         else for (;;)                                                   \
  99           if (1) goto MCTRL__LABEL(tag##__wrap_break);                  \
 100           else for (;;)                                                 \
 101             if (1) goto MCTRL__LABEL(tag##__wrap_end);                  \
 102             else MCTRL__LABEL(tag##__wrap_body):
 103
 104 /* @ALLOWELSE(tag, before, onend, onbreak) stmt_0 [else stmt_1]@
 105  * @GOELSE(tag);@
 106  *
 107  * Execute the @before@ statement, followed by @stmt_0@.  If @stmt_0@
 108  * completes, or invokes @break@ or @continue@, then control continues with
 109  * the next statement.  If @GOELSE(tag)@ is invoked anywhere in the
 110  * function, then @before@ is executed, followed by @stmt_1@ (if present).
 111  * If @stmt_1@ invokes @break@ then control passes to @onbreak@; if @stmt_1@
 112  * ends normally then control passes to @onend@.  Any @break@ and @continue@
 113  * in the @before@, @onend@, and @onbreak@ statements behave as one would
 114  * expect from their context.
 115  */
 116 #define ALLOWELSE(tag, before, onend, onbreak)                          \
 117         if (1) goto MCTRL__LABEL(tag##__allowelse_body);                \
 118         else if (1) MCTRL__LABEL(tag##__allowelse_body_end): ;          \
 119         else if (1) { MCTRL__LABEL(tag##__allowelse_else_end): onend }  \
 120         else if (1) { MCTRL__LABEL(tag##__allowelse_else_break): onbreak } \
 121         else if (1) {                                                   \
 122         MCTRL__LABEL(tag##__allowelse_before_else):                     \
 123           before goto MCTRL__LABEL(tag##__allowelse_else);              \
 124         } else for (;;)                                                 \
 125           if (1) goto MCTRL__LABEL(tag##__allowelse_else_break);        \
 126           else for (;;)                                                 \
 127             if (1) goto MCTRL__LABEL(tag##__allowelse_else_end);        \
 128             else MCTRL__LABEL(tag##__allowelse_else): if (0) for (;;)   \
 129               if (1) goto MCTRL__LABEL(tag##__allowelse_body_end);      \
 130               else MCTRL__LABEL(tag##__allowelse_body):
 131 #define GOELSE(tag)                                                     \
 132         goto MCTRL__LABEL(tag##__allowelse_before_else)
 133
 134 /* @DOWHILE(tag, cond) stmt@
 135  *
 136  * Repeatedly execute @stmt@ until @cond@ evaluates to zero.  Execute @stmt@
 137  * at least once.  The @break@ and @continue@ statements work within @stmt@
 138  * as one would expect.
 139  */
 140 #define DOWHILE(tag, cond)                                              \
 141         if (1) goto MCTRL__LABEL(tag##__dowhile_body);                  \
 142         else while (cond) MCTRL__LABEL(tag##__dowhile_body):
 143
 144 /* @DECL(tag, decl) stmt@
 145  *
 146  * Execute @stmt@ with @decl@ in scope.  If @stmt@ completes or invokes
 147  * @break@ or @continue@ then control continues with the statement following
 148  * @DECL@.  Internally, this uses @for@, so it only works in C99 or later, or
 149  * C++.
 150  */
 151 #if __STDC_VERSION__ >= 199901 || defined(__cplusplus)
 152 #  define DECL(tag, decl)                                               \
 153         for (decl;;)                                                    \
 154           if (1) goto MCTRL__LABEL(tag##__decl_body);                   \
 155           else if (1) MCTRL__LABEL(tag##__decl_exit): break;            \
 156           else for (;;)                                                 \
 157             if (1) goto MCTRL__LABEL(tag##__decl_exit);                 \
 158             else MCTRL__LABEL(tag##__decl_body):
 159 #endif
 160
 161 /*----- That's all, folks -------------------------------------------------*/
 162
 163 #ifdef __cplusplus
 164   }
 165 #endif
 166
 167 #endif