[gtk/input-tweaks: 3/7] composetable: Add a prefix api

[Matthias Clasen <matthiasc src gnome org>]

commit 914edb1472b322c7bfe081e34671398f715476d4
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jul 29 08:23:40 2021 -0400

    composetable: Add a prefix api
    
    Add a function that computes the longest prefix
    of a buffer for which a compose table has matches.

 gtk/gtkcomposetable.c | 41 +++++++++++++++++++++++++++++++++++++++++
 gtk/gtkcomposetable.h |  5 +++++
 2 files changed, 46 insertions(+)
---
diff --git a/gtk/gtkcomposetable.c b/gtk/gtkcomposetable.c
index 40dd8b6e41..0d9488c214 100644
--- a/gtk/gtkcomposetable.c
+++ b/gtk/gtkcomposetable.c
@@ -1352,6 +1352,47 @@ gtk_compose_table_check (const GtkComposeTable *table,
   return FALSE;
 }
 
+void
+gtk_compose_table_get_prefix (const GtkComposeTable *table,
+                              const guint16         *compose_buffer,
+                              int                    n_compose,
+                              int                   *prefix)
+{
+  int index_stride = table->max_seq_len + 1;
+  int p = 0;
+
+  for (int idx = 0; idx < table->n_index_size; idx++)
+    {
+      const guint16 *seq_index = table->data + (idx * index_stride);
+
+      if (seq_index[0] == compose_buffer[0])
+        {
+          p = 1;
+
+          for (int i = 1; i < table->max_seq_len; i++)
+            {
+              int len = i + 1;
+
+              for (int j = seq_index[i]; j < seq_index[i + 1]; j += len)
+                {
+                  int k;
+
+                  for (k = 0; k < MIN (len, n_compose) - 1; k++)
+                    {
+                      if (compose_buffer[k + 1] != (gunichar) table->data[j + k])
+                        break;
+                    }
+                  p = MAX (p, k + 1);
+                }
+            }
+
+          break;
+        }
+    }
+
+  *prefix = p;
+}
+
 void
 gtk_compose_table_foreach (const GtkComposeTable      *table,
                            GtkComposeSequenceCallback  callback,
diff --git a/gtk/gtkcomposetable.h b/gtk/gtkcomposetable.h
index 1398559a66..e9adc50150 100644
--- a/gtk/gtkcomposetable.h
+++ b/gtk/gtkcomposetable.h
@@ -80,6 +80,11 @@ gboolean          gtk_compose_table_check   (const GtkComposeTable *table,
                                              gboolean              *compose_match,
                                              GString               *output);
 
+void              gtk_compose_table_get_prefix (const GtkComposeTable *table,
+                                                const guint16         *compose_buffer,
+                                                int                    n_compose,
+                                                int                   *prefix);
+
 gboolean          gtk_check_algorithmically (const guint16         *compose_buffer,
                                              int                    n_compose,
                                              gunichar              *output);