Changed the various functions searching for tags in ExifTagTable[]

to use a binary search. This single change increases the speed of
a run through the libexif-testsuite by 7%

diff --git a/ChangeLog b/ChangeLog
index d99700f..82a3d15 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2009-10-14  Dan Fandrich <dan@coneharvesters.com>
+
+       * Changed the various functions searching for tags in ExifTagTable[]
+         to use a binary search. This single change increases the speed of
+         a run through the libexif-testsuite by 7%
+
 2009-10-13  Dan Fandrich <dan@coneharvesters.com>
 
        * po/sv.po: Updated Swedish translation by Daniel Nylander

diff --git a/NEWS b/NEWS
index 573b8ce..113659d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,5 @@
 libexif-0.6.x:
+  * Now using a binary search to make searching through the tag table faster
 
 
 libexif-0.6.18 (2009-10-09):

diff --git a/libexif/exif-tag.c b/libexif/exif-tag.c
index 3f113aa..a78bbf9 100644 (file)
--- a/libexif/exif-tag.c
+++ b/libexif/exif-tag.c
@@ -47,7 +47,7 @@
  * The entries MUST be sorted in tag order.
  * The name and title are mandatory, but the description may be NULL.
  */
-static const struct {
+static const struct TagEntry {
        /*! Tag ID. There may be duplicate tags when the same number is used for
         * different meanings in different IFDs. */
        ExifTag tag;
@@ -877,12 +877,57 @@ exif_tag_table_get_name (unsigned int n)
        return (n < exif_tag_table_count ()) ? ExifTagTable[n].name : NULL;
 }
 
+/*!
+ * Return the number of entries in the EXIF tag table, including the
+ * terminating NULL entry.
+ */
 unsigned int
 exif_tag_table_count (void)
 {
        return sizeof (ExifTagTable) / sizeof (ExifTagTable[0]);
 }
 
+
+/*!
+ * Compares the tag with that in entry.
+ * \param[in] tag pointer to integer tag value
+ * \param[in] entry pointer to a struct TagEntry
+ * \return 0 if tags are equal, <0 if tag < entry, >0 if tag > entry
+ */
+static int
+match_tag(const void *tag, const void *entry)
+{
+       return *(int*)tag - ((struct TagEntry *)entry)->tag;
+}
+
+
+/*!
+ * Finds the first entry in the EXIF tag table with the given tag number
+ * using a binary search.
+ * \param[in] tag to find
+ * \return index into table, or -1 if not found
+ */
+static int
+exif_tag_table_first(ExifTag tag)
+{
+       int i;
+       struct TagEntry *entry = bsearch(&tag, ExifTagTable,
+                       exif_tag_table_count()-1, sizeof(struct TagEntry), match_tag);
+       if (!entry)
+                       return -1;      /* Not found */
+
+       /* Calculate index of found entry */
+       i = entry - ExifTagTable;
+
+       /* There may be other entries with the same tag number, so search
+        * backwards to find the first
+        */
+       while ((i > 0) && (ExifTagTable[i-1].tag == tag)) {
+               --i;
+       }
+       return i;
+}
+
 #define RECORDED \
 ((ExifTagTable[i].esl[ifd][EXIF_DATA_TYPE_UNCOMPRESSED_CHUNKY] != EXIF_SUPPORT_LEVEL_NOT_RECORDED) || \
  (ExifTagTable[i].esl[ifd][EXIF_DATA_TYPE_UNCOMPRESSED_PLANAR] != EXIF_SUPPORT_LEVEL_NOT_RECORDED) || \
@@ -893,9 +938,14 @@ const char *
 exif_tag_get_name_in_ifd (ExifTag tag, ExifIfd ifd)
 {
        unsigned int i;
+       int first;
 
-       if (ifd >= EXIF_IFD_COUNT) return NULL;
-       for (i = 0; ExifTagTable[i].name; i++)
+       if (ifd >= EXIF_IFD_COUNT)
+               return NULL;
+       first = exif_tag_table_first(tag);
+       if (first < 0)
+               return NULL;
+       for (i = first; ExifTagTable[i].name; i++)
                if ((ExifTagTable[i].tag == tag) && RECORDED) break;
        return ExifTagTable[i].name;
 }
@@ -904,6 +954,7 @@ const char *
 exif_tag_get_title_in_ifd (ExifTag tag, ExifIfd ifd)
 {
        unsigned int i;
+       int first;
 
        /* FIXME: This belongs to somewhere else. */
        /* libexif should use the default system locale.
@@ -913,8 +964,12 @@ exif_tag_get_title_in_ifd (ExifTag tag, ExifIfd ifd)
         * bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
         */
        bindtextdomain (GETTEXT_PACKAGE, LOCALEDIR);
-       if (ifd >= EXIF_IFD_COUNT) return NULL;
-       for (i = 0; ExifTagTable[i].title; i++)
+       if (ifd >= EXIF_IFD_COUNT)
+               return NULL;
+       first = exif_tag_table_first(tag);
+       if (first < 0)
+               return NULL;
+       for (i = first; ExifTagTable[i].title; i++)
                if ((ExifTagTable[i].tag == tag) && RECORDED) break;
        return _(ExifTagTable[i].title);
 }
@@ -923,6 +978,7 @@ const char *
 exif_tag_get_description_in_ifd (ExifTag tag, ExifIfd ifd)
 {
        unsigned int i;
+       int first;
 
        /* libexif should use the default system locale.
         * If an application specifically requires UTF-8, then we
@@ -932,7 +988,11 @@ exif_tag_get_description_in_ifd (ExifTag tag, ExifIfd ifd)
         */
        bindtextdomain (GETTEXT_PACKAGE, LOCALEDIR);
 
-       if (ifd >= EXIF_IFD_COUNT) return NULL;
+       if (ifd >= EXIF_IFD_COUNT)
+               return NULL;
+       first = exif_tag_table_first(tag);
+       if (first < 0)
+               return NULL;
        for (i = 0; ExifTagTable[i].description; i++)
                if ((ExifTagTable[i].tag == tag) && RECORDED) {
                        /* GNU gettext acts strangely when given an empty string */
@@ -987,7 +1047,7 @@ exif_tag_get_title (ExifTag tag)
 const char *
 exif_tag_get_description (ExifTag tag)
 {
-       return exif_tag_get_stuff (tag, exif_tag_get_description_in_ifd);
+       return exif_tag_get_stuff(tag, exif_tag_get_description_in_ifd);
 }
 
 
@@ -1021,12 +1081,17 @@ static inline ExifSupportLevel
 get_support_level_in_ifd (ExifTag tag, ExifIfd ifd, ExifDataType t)
 {
        unsigned int i;
-       for (i = 0; ExifTagTable[i].description; i++) {
+       int first = exif_tag_table_first(tag);
+       if (first < 0)
+               return EXIF_SUPPORT_LEVEL_NOT_RECORDED;
+       for (i = first; ExifTagTable[i].name; i++) {
                if (ExifTagTable[i].tag == tag) {
                        const ExifSupportLevel supp = ExifTagTable[i].esl[ifd][t];
                        if (supp != EXIF_SUPPORT_LEVEL_NOT_RECORDED)
                                return supp;
                        /* Try looking for another entry */
+               } else {
+                       break; /* We've reached the end of the matching tags */
                }
        }
        return EXIF_SUPPORT_LEVEL_NOT_RECORDED;
@@ -1045,7 +1110,11 @@ static inline ExifSupportLevel
 get_support_level_any_type (ExifTag tag, ExifIfd ifd)
 {
        unsigned int i;
-       for (i = 0; ExifTagTable[i].description; i++) {
+       int first = exif_tag_table_first(tag);
+       if (first < 0)
+               return EXIF_SUPPORT_LEVEL_UNKNOWN;
+
+       for (i = first; ExifTagTable[i].name; i++) {
                if (ExifTagTable[i].tag == tag) {
                        /*
                         * Check whether the support level is the same for all possible
@@ -1064,6 +1133,8 @@ get_support_level_any_type (ExifTag tag, ExifIfd ifd)
                                        return supp;
                        }
                        /* Keep searching the table for another tag for our IFD */
+               } else {
+                       break; /* We've reached the end of the matching tags */
                }
        }
        return EXIF_SUPPORT_LEVEL_UNKNOWN;