Track shortest string in each among in analyser

This refactor eliminates duplicate code from the C and Ada generators,
and means this data is available to other generators that want to use
it.

compiler/analyser.c

@@ -1,4 +1,5 @@
 #include <assert.h>
+#include <limits.h>  /* for INT_MAX */
 #include <stdio.h>   /* printf etc */
 #include <stdlib.h>  /* exit */
 #include <string.h>  /* memmove */
@@ -760,6 +761,7 @@ static struct node * make_among(struct analyser * a, struct node * p, struct nod
     x->nocommand_count = 0;
     x->amongvar_needed = false;
     x->always_matches = false;
+    x->shortest_size = INT_MAX;
 
     if (q->type == c_bra) { starter = q; q = q->right; }
 
@@ -847,6 +849,8 @@ static struct node * make_among(struct analyser * a, struct node * p, struct nod
         int size = w0->size;
         struct amongvec * w;
 
+        if (size && size < x->shortest_size) x->shortest_size = size;
+
         for (w = w0 - 1; w >= v; w--) {
             if (w->size < size && memcmp(w->b, b, w->size * sizeof(symbol)) == 0) {
                 w0->i = w - v;  /* fill in index of longest substring */

compiler/generator.c

@@ -1,5 +1,4 @@
 #include <assert.h>
-#include <limits.h>  /* for INT_MAX */
 #include <stdio.h>   /* for fprintf etc */
 #include <stdlib.h>  /* for free etc */
 #include <string.h>  /* for strlen */
@@ -1460,7 +1459,7 @@ static void generate_substring(struct generator * g, struct node * p) {
     int empty_case = -1;
     int n_cases = 0;
     symbol cases[2];
-    int shortest_size = INT_MAX;
+    int shortest_size = x->shortest_size;
     int shown_comment = 0;
 
     g->S[0] = p->mode == m_forward ? "" : "_b";
@@ -1474,13 +1473,6 @@ static void generate_substring(struct generator * g, struct node * p) {
      * In backward mode, we can't match if there are fewer characters before
      * the current position than the minimum length.
      */
-    for (c = 0; c < x->literalstring_count; ++c) {
-        int size = among_cases[c].size;
-        if (size != 0 && size < shortest_size) {
-            shortest_size = size;
-        }
-    }
-
     for (c = 0; c < x->literalstring_count; ++c) {
         symbol ch;
         if (among_cases[c].size == 0) {

compiler/generator_ada.c

@@ -3,7 +3,6 @@
 #include <string.h> /* for strlen */
 #include <stdio.h> /* for fprintf etc */
 #include <ctype.h>
-#include <limits.h>
 #include "header.h"
 
 /* prototypes */
@@ -1164,7 +1163,7 @@ static void generate_substring(struct generator * g, struct node * p) {
     int empty_case = -1;
     int n_cases = 0;
     symbol cases[2];
-    int shortest_size = INT_MAX;
+    int shortest_size = x->shortest_size;
     int call_done = 0;
     int need_among_handler = (x->function_count > 0);
 
@@ -1180,13 +1179,6 @@ static void generate_substring(struct generator * g, struct node * p) {
      * In backward mode, we can't match if there are fewer characters before
      * the current position than the minimum length.
      */
-    for (c = 0; c < x->literalstring_count; ++c) {
-        int size = among_cases[c].size;
-        if (size != 0 && size < shortest_size) {
-            shortest_size = size;
-        }
-    }
-
     for (c = 0; c < x->literalstring_count; ++c) {
         symbol ch;
         if (among_cases[c].size == 0) {

compiler/header.h

@@ -242,6 +242,7 @@ struct among {
     int function_count;       /* in this among */
     int amongvar_needed;      /* do we need to set among_var? */
     int always_matches;       /* will this among always match? */
+    int shortest_size;        /* smallest non-zero string length in this among */
     struct node * substring;  /* i.e. substring ... among ( ... ) */
     struct node ** commands;  /* array with command_count entries */
 };