[src/trunk]: src/usr.bin/indent indent: extract reduce_stmt from reduce

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/5fee4675873f
branches:  trunk
changeset: 960158:5fee4675873f
user:      rillig <rillig%NetBSD.org@localhost>
date:      Tue Mar 09 18:21:01 2021 +0000

description:
indent: extract reduce_stmt from reduce

This refactoring reduces the indentation of the code, as well as
removing any ambiguity as to which 'switch' statement a 'break' belongs,
as there are no more nested 'switch' statements.

No functional change.

diffstat:

 usr.bin/indent/parse.c |  168 ++++++++++++++++++------------------------------
 1 files changed, 65 insertions(+), 103 deletions(-)

diffs (190 lines):

diff -r 460da241cf37 -r 5fee4675873f usr.bin/indent/parse.c
--- a/usr.bin/indent/parse.c    Tue Mar 09 16:48:28 2021 +0000
+++ b/usr.bin/indent/parse.c    Tue Mar 09 18:21:01 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: parse.c,v 1.15 2021/03/09 16:48:28 rillig Exp $        */
+/*     $NetBSD: parse.c,v 1.16 2021/03/09 18:21:01 rillig Exp $        */
 
 /*-
  * SPDX-License-Identifier: BSD-4-Clause
@@ -232,116 +232,78 @@
 #endif
 }
 
+/*----------------------------------------------*\
+|   REDUCTION PHASE                             |
+\*----------------------------------------------*/
+
 /*
- * NAME: reduce
- *
- * FUNCTION: Implements the reduce part of the parsing algorithm
- *
- * ALGORITHM: The following reductions are done.  Reductions are repeated
- *     until no more are possible.
- *
- * Old TOS             New TOS
- * <stmt> <stmt>       <stmtl>
- * <stmtl> <stmt>      <stmtl>
- * do <stmt>           "dostmt"
- * if <stmt>           "ifstmt"
- * switch <stmt>       <stmt>
- * decl <stmt>         <stmt>
- * "ifelse" <stmt>     <stmt>
- * for <stmt>          <stmt>
- * while <stmt>                <stmt>
- * "dostmt" while      <stmt>
+ * Try to combine the statement on the top of the parse stack with the symbol
+ * directly below it, replacing these two symbols with a single symbol.
+ */
+static int
+reduce_stmt(void)
+{
+    switch (ps.p_stack[ps.tos - 1]) {
+
+    case stmt:         /* stmt stmt */
+    case stmtl:                /* stmtl stmt */
+       ps.p_stack[--ps.tos] = stmtl;
+       return true;
+
+    case dolit:                /* do <stmt> */
+       ps.p_stack[--ps.tos] = dohead;
+       ps.i_l_follow = ps.il[ps.tos];
+       return true;
+
+    case ifstmt:       /* if (<expr>) <stmt> */
+       ps.p_stack[--ps.tos] = ifhead;
+       int i = ps.tos - 1;
+       while (ps.p_stack[i] != stmt &&
+              ps.p_stack[i] != stmtl &&
+              ps.p_stack[i] != lbrace)
+           --i;
+       ps.i_l_follow = ps.il[i];
+       /*
+        * for the time being, we will assume that there is no else on
+        * this if, and set the indentation level accordingly. If an
+        * else is scanned, it will be fixed up later
+        */
+       return true;
+
+    case swstmt:       /* switch (<expr>) <stmt> */
+       case_ind = ps.cstk[ps.tos - 1];
+       /* FALLTHROUGH */
+    case decl:         /* finish of a declaration */
+    case elsehead:     /* if (<expr>) <stmt> else <stmt> */
+    case forstmt:      /* for (<...>) <stmt> */
+    case whilestmt:    /* while (<expr>) <stmt> */
+       ps.p_stack[--ps.tos] = stmt;
+       ps.i_l_follow = ps.il[ps.tos];
+       return true;
+
+    default:           /* <anything else> <stmt> */
+       return false;
+    }
+}
+
+/*
+ * Repeatedly try to reduce the top two symbols on the parse stack to a
+ * single symbol, until no more reductions are possible.
  *
  * On each reduction, ps.i_l_follow (the indentation for the following line)
  * is set to the indentation level associated with the old TOS.
- *
- * PARAMETERS: None
- *
- * RETURNS: Nothing
- *
- * GLOBALS: ps.cstk ps.i_l_follow = ps.il ps.p_stack = ps.tos =
- *
- * CALLS: None
- *
- * CALLED BY: parse
- *
- * HISTORY: initial coding     November 1976   D A Willcox of CAC
- *
  */
-/*----------------------------------------------*\
-|   REDUCTION PHASE                             |
-\*----------------------------------------------*/
 static void
 reduce(void)
 {
-    int i;
-
-    for (;;) {                 /* keep looping until there is nothing left to
-                                * reduce */
-
-       switch (ps.p_stack[ps.tos]) {
-
-       case stmt:
-           switch (ps.p_stack[ps.tos - 1]) {
-
-           case stmt:          /* stmt stmt */
-           case stmtl:         /* stmtl stmt */
-               ps.p_stack[--ps.tos] = stmtl;
-               break;
-
-           case dolit:         /* <do> <stmt> */
-               ps.p_stack[--ps.tos] = dohead;
-               ps.i_l_follow = ps.il[ps.tos];
-               break;
-
-           case ifstmt:        /* <if> <stmt> */
-               ps.p_stack[--ps.tos] = ifhead;
-               for (i = ps.tos - 1;
-                       (
-                        ps.p_stack[i] != stmt
-                        &&
-                        ps.p_stack[i] != stmtl
-                        &&
-                        ps.p_stack[i] != lbrace
-                        );
-                       --i);
-               ps.i_l_follow = ps.il[i];
-               /*
-                * for the time being, we will assume that there is no else on
-                * this if, and set the indentation level accordingly. If an
-                * else is scanned, it will be fixed up later
-                */
-               break;
-
-           case swstmt:        /* <switch> <stmt> */
-               case_ind = ps.cstk[ps.tos - 1];
-               /* FALLTHROUGH */
-           case decl:          /* finish of a declaration */
-           case elsehead:      /* <if> <stmt> else> <stmt> */
-           case forstmt:       /* <for> <stmt> */
-           case whilestmt:     /* <while> <stmt> */
-               ps.p_stack[--ps.tos] = stmt;
-               ps.i_l_follow = ps.il[ps.tos];
-               break;
-
-           default:            /* <anything else> <stmt> */
-               return;
-
-           }                   /* end of section for <stmt> on top of stack */
-           break;
-
-       case whilestmt:         /* while (...) on top */
-           if (ps.p_stack[ps.tos - 1] == dohead) {
-               /* it is termination of a do while */
-               ps.tos -= 2;
-               break;
-           }
-           else
-               return;
-
-       default:                /* anything else on top */
-           return;
-
+again:
+    if (ps.p_stack[ps.tos] == stmt) {
+       if (reduce_stmt())
+           goto again;
+    } else if (ps.p_stack[ps.tos] == whilestmt) {
+       if (ps.p_stack[ps.tos - 1] == dohead) {
+           ps.tos -= 2;
+           goto again;
        }
     }
 }