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) 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 for (;;)                                                   \
  82           if (1) { stmt break; }                                        \
  83           else MCTRL__LABEL(tag##__after_body):
  84
  85 /* @WRAP(tag, before, onend, onbreak) stmt@
  86  *
  87  * Execute the @before@ statement, followed by @stmt@.  If @stmt@ invokes
  88  * @break@, then @onbreak@ is immediately executed; if @stmt@ completes
  89  * normally, or invokes @continue@ then @onend@ is immediately executed.
  90  * Any @break@ and @continue@ in the @before@, @onend@, and @onbreak@
  91  * statements behave as one would expect from their context.
  92  */
  93 #define WRAP(tag, before, onend, onbreak)                               \
  94         if (1) { before goto MCTRL__LABEL(tag##__wrap_body); }          \
  95         else if (1) MCTRL__LABEL(tag##__wrap_end): onend                \
  96         else if (1) MCTRL__LABEL(tag##__wrap_break): onbreak            \
  97         else for (;;)                                                   \
  98           if (1) goto MCTRL__LABEL(tag##__wrap_break);                  \
  99           else for (;;)                                                 \
 100             if (1) goto MCTRL__LABEL(tag##__wrap_end);                  \
 101             else MCTRL__LABEL(tag##__wrap_body):
 102
 103 /* @ALLOWELSE(tag, before, onend, onbreak) stmt_0 [else stmt_1]@
 104  * @GOELSE(tag);@
 105  *
 106  * Execute the @before@ statement, followed by @stmt_0@.  If @stmt_0@
 107  * completes, or invokes @break@ or @continue@, then control continues with
 108  * the next statement.  If @GOELSE(tag)@ is invoked anywhere in the
 109  * function, then @before@ is executed, followed by @stmt_1@ (if present).
 110  * If @stmt_1@ invokes @break@ then control passes to @onbreak@; if @stmt_1@
 111  * ends normally then control passes to @onend@.  Any @break@ and @continue@
 112  * in the @before@, @onend@, and @onbreak@ statements behave as one would
 113  * expect from their context.
 114  */
 115 #define ALLOWELSE(tag, before, onend, onbreak)                          \
 116         if (1) goto MCTRL__LABEL(tag##__allowelse_body);                \
 117         else if (1) MCTRL__LABEL(tag##__allowelse_body_end): ;          \
 118         else if (1) MCTRL__LABEL(tag##__allowelse_else_end): onend      \
 119         else if (1) MCTRL__LABEL(tag##__allowelse_else_break): onbreak  \
 120         else if (1) MCTRL__LABEL(tag##__allowelse_before_else):         \
 121           { before goto MCTRL__LABEL(tag##__allowelse_else); }          \
 122         else for (;;)                                                   \
 123           if (1) goto MCTRL__LABEL(tag##__allowelse_else_break);        \
 124           else for (;;)                                                 \
 125             if (1) goto MCTRL__LABEL(tag##__allowelse_else_end);        \
 126             else MCTRL__LABEL(tag##__allowelse_else): if (0) for (;;)   \
 127               if (1) goto MCTRL__LABEL(tag##__allowelse_body_end);      \
 128               else MCTRL__LABEL(tag##__allowelse_body):
 129 #define GOELSE(tag)                                                     \
 130         goto MCTRL__LABEL(tag##__allowelse_before_else)
 131
 132 /* @DOWHILE(tag, cond) stmt@
 133  *
 134  * Repeatedly execute @stmt@ until @cond@ evaluates to zero.  Execute @stmt@
 135  * at least once.  The @break@ and @continue@ statements work within @stmt@
 136  * as one would expect.
 137  */
 138 #define DOWHILE(tag, cond)                                              \
 139         if (1) goto MCTRL__LABEL(tag##__dowhile_body);                  \
 140         else while (cond) MCTRL__LABEL(tag##__dowhile_body):
 141
 142 /* @DECL(tag, decl) stmt@
 143  *
 144  * Execute @stmt@ with @decl@ in scope.  If @stmt@ completes or invokes
 145  * @break@ or @continue@ then control continues with the statement following
 146  * @DECL@.  Internally, this uses @for@, so it only works in C99 or later, or
 147  * C++.
 148  */
 149 #if __STDC_VERSION__ >= 199901 || defined(__cplusplus)
 150 #  define DECL(tag, decl)                                               \
 151         for (decl;;)                                                    \
 152           if (1) goto MCTRL__LABEL(tag##__decl_body);                   \
 153           else if (1) MCTRL__LABEL(tag##__decl_exit): break;            \
 154           else for (;;)                                                 \
 155             if (1) goto MCTRL__LABEL(tag##__decl_exit);                 \
 156             else MCTRL__LABEL(tag##__decl_body):
 157 #endif
 158
 159 /*----- That's all, folks -------------------------------------------------*/
 160
 161 #ifdef __cplusplus
 162   }
 163 #endif
 164
 165 #endif