[libgit2-glib] Add ggit_oid_has_prefix

[Jesse van den Kieboom <jessevdk src gnome org>]

commit a606c69fac05d4610163a970f200edec8bc46dc5
Author: Jesse van den Kieboom <jessevdk gmail com>
Date:   Mon Jan 5 21:09:46 2015 +0100

    Add ggit_oid_has_prefix

 libgit2-glib/ggit-oid.c |   78 +++++++++++++++++++++++++++++++++++++++++++++++
 libgit2-glib/ggit-oid.h |    3 ++
 2 files changed, 81 insertions(+), 0 deletions(-)
---
diff --git a/libgit2-glib/ggit-oid.c b/libgit2-glib/ggit-oid.c
index 303f2ed..c185eca 100644
--- a/libgit2-glib/ggit-oid.c
+++ b/libgit2-glib/ggit-oid.c
@@ -234,4 +234,82 @@ ggit_oid_is_zero (GgitOId const *oid)
        return git_oid_iszero (&oid->oid) == 1;
 }
 
+static gint
+c_to_h (gchar c)
+{
+       if (c >= '0' && c <= '9')
+       {
+               return c - '0';
+       }
+       else if (c >= 'A' && c <= 'F')
+       {
+               return 10 + (c - 'A');
+       }
+       else if (c >= 'a' && c <= 'f')
+       {
+               return 10 + (c - 'a');
+       }
+       else
+       {
+               return -1;
+       }
+}
+
+/**
+ * ggit_oid_has_prefix:
+ * @oid: a #GgitOId.
+ * @prefix: a prefix.
+ *
+ * Check whether the object id has a given prefix. Note that the prefix is
+ * specified in hexadecimal ASCII.
+ *
+ * Returns: %TRUE if the id has the given prefix, %FALSE otherwise.
+ */
+gboolean
+ggit_oid_has_prefix (GgitOId     *oid,
+                     const gchar *str)
+{
+       gint i;
+
+       for (i = 0; i < GIT_OID_RAWSZ; ++i)
+       {
+               gint v1;
+
+               if (*str == '\0')
+               {
+                       return TRUE;
+               }
+
+               v1 = c_to_h (*str++);
+
+               if (v1 == -1)
+               {
+                       return FALSE;
+               }
+
+               if (*str != '\0')
+               {
+                       gint v2;
+
+                       v2 = c_to_h (*str++);
+
+                       if (v2 == -1)
+                       {
+                               return FALSE;
+                       }
+
+                       if (oid->oid.id[i] != (v1 << 4) + v2)
+                       {
+                               return FALSE;
+                       }
+               }
+               else if (oid->oid.id[i] >> 4 != v1)
+               {
+                       return FALSE;
+               }
+       }
+
+       return *str == '\0';
+}
+
 /* ex:set ts=8 noet: */
diff --git a/libgit2-glib/ggit-oid.h b/libgit2-glib/ggit-oid.h
index b8e123c..aca417d 100644
--- a/libgit2-glib/ggit-oid.h
+++ b/libgit2-glib/ggit-oid.h
@@ -56,6 +56,9 @@ gboolean       ggit_oid_equal           (GgitOId const *a,
 
 gboolean       ggit_oid_is_zero         (GgitOId const *oid);
 
+gboolean       ggit_oid_has_prefix      (GgitOId       *oid,
+                                         const gchar   *prefix);
+
 G_END_DECLS
 
 #endif /* __GGIT_OID_H__ */