Add prefixes to arrays

4 files changed, 68 insertions, 8 deletions

diff --git a/Makefile.am b/Makefile.am
index 530e464..485385a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -25,13 +25,17 @@ libnul_la_LIBADD = @DEP_LIBS@ libffi/libffi_convenience.la
 
 libnul_la_LDFLAGS = -no-undefined
 
-noinst_PROGRAMS = example dbw-example
+noinst_PROGRAMS = example dbw-example prefix-test
+
 example_SOURCES = example.c
 example_LDADD = $(top_builddir)/libnul.la
 
 dbw_example_SOURCES = dbw-example.c
 dbw_example_LDADD = $(top_builddir)/libnul.la
 
+prefix_test_SOURCES = prefix-test.c
+prefix_test_LDADD = $(top_builddir)/libnul.la
+
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = libnul.pc
 
diff --git a/array.c b/array.c
index d436414..f8e9b82 100644
--- a/array.c
+++ b/array.c
@@ -39,6 +39,7 @@ struct array_t
     gssize     n_elements;	/* Number of elements in use, not including
 				 * the nul terminator
 				 */
+    gssize     n_prefix_bytes;	/* Number of data bytes used for the application prefix */
     align_t    data[1];
 };
 
@@ -65,7 +66,10 @@ array_free (void *data, const int *magic)
 static void
 nul_terminate (array_t *array)
 {
-    char *end = (char *)array->data + array->n_elements * array->element_size;
+    char *end = (char *)array->data;
+
+    end += array->n_prefix_bytes;
+    end += array->n_elements * array->element_size;
 
     memset (end, 0, array->element_size);
 }
@@ -78,6 +82,7 @@ realloc_array (array_t *array, int n_elements)
     /* FIXME: overflow? */
     n_bytes = NUL_STRUCT_OFFSET (array_t, data);
     n_bytes += (n_elements + 1) * array->element_size;
+    n_bytes += array->n_prefix_bytes;
     
     if (n_bytes > array->n_bytes)
     {
@@ -97,12 +102,13 @@ realloc_array (array_t *array, int n_elements)
 }
 
 static void *
-array_new (int element_size, const int *magic)
+array_new (int element_size, const int *magic, int n_prefix_bytes)
 {
     array_t *array = g_new (array_t, 1);
     
     array->magic = magic;
     array->element_size = element_size;
+    array->n_prefix_bytes = n_prefix_bytes;
     array->n_bytes = sizeof (array_t);
     array->n_elements = 0;
 
@@ -117,13 +123,16 @@ array_delete_head (void *data, const int *magic, gssize n_elements)
     array_t *array = get_array (data, magic);
     int n_bytes = n_elements * array->element_size;
     int n_total = array->n_elements * array->element_size;
+    char *first;
 
     if (n_elements < 0 || n_elements > array->n_elements)
 	n_bytes = n_total;
     
     /* FIXME: this should be done in constant time */
+
+    first = (char *)array->data + array->n_prefix_bytes;
     
-    memmove (array->data, (char *)array->data + n_bytes, n_total - n_bytes);
+    memmove (first, first + n_bytes, n_total - n_bytes);
     
     array->n_elements -= n_elements;
     
@@ -158,7 +167,7 @@ array_append_undefined (void *data,
     nul_terminate (array);
 
     if (tail)
-	*tail = (char *)array->data + array->element_size * (array->n_elements - n_elements);
+	*tail = (char *)array->data + array->n_prefix_bytes + array->element_size * (array->n_elements - n_elements);
 
     return array->data;
 }
@@ -205,7 +214,13 @@ static const int arr_t_magic;
 nul_ptr_t
 nul_array_new (int element_size)
 {
-    return array_new (element_size, &arr_t_magic);
+    return array_new (element_size, &arr_t_magic, 0);
+}
+
+nul_ptr_t
+nul_array_new_prefix (int element_size, int prefix_size)
+{
+    return array_new (element_size, &arr_t_magic, prefix_size);
 }
 
 nul_ptr_t
@@ -256,7 +271,7 @@ static const int parr_t_magic;
 void **
 nul_ptr_array_new (void)
 {
-    return array_new (sizeof (void *), &parr_t_magic);
+    return array_new (sizeof (void *), &parr_t_magic, 0);
 }
 
 void **
@@ -285,7 +300,7 @@ static const int string_t_magic;
 nul_string_t *
 nul_string_new (void)
 {
-    return array_new (sizeof (char), &string_t_magic);
+    return array_new (sizeof (char), &string_t_magic, 0);
 }
 
 void
diff --git a/libnul.h b/libnul.h
index f22acf7..3bf4106 100644
--- a/libnul.h
+++ b/libnul.h
@@ -53,6 +53,7 @@ typedef void * const nul_const_ptr_t;
  * Generic arrays
  */
 nul_ptr_t  nul_array_new        (int element_size) NUL_UR;
+nul_ptr_t  nul_array_new_prefix (int element_size, int prefix_size); NUL_UR;
 nul_ptr_t  nul_array_append     (nul_ptr_t array, nul_ptr_t element) NUL_UR;
 gsize      nul_array_len        (nul_ptr_t array);
 void       nul_array_free       (nul_ptr_t array);
diff --git a/prefix-test.c b/prefix-test.c
new file mode 100644
index 0000000..5c44562
--- /dev/null
+++ b/prefix-test.c
@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <libnul.h>
+
+typedef struct
+{
+    int a;
+    int b;
+    char *x;
+
+    int data[1];
+    
+} prefixed_t;
+
+
+int
+main (void)
+{
+    int i;
+    prefixed_t *prefixed = nul_array_new_prefix (
+	sizeof (int), NUL_STRUCT_OFFSET (prefixed_t, data));
+
+    prefixed->a = 0xaaaaaaaa;
+    prefixed->b = 0xbbbbbbbb;
+    prefixed->x = "HI!";
+
+    i = 0;
+    prefixed = nul_array_append (prefixed, &i); i++;
+    prefixed = nul_array_append (prefixed, &i); i++;
+    prefixed = nul_array_append (prefixed, &i); i++;
+    prefixed = nul_array_append (prefixed, &i); i++;
+    prefixed = nul_array_append (prefixed, &i); i++;
+    prefixed = nul_array_append (prefixed, &i); i++;
+
+    for (i = 0; i < nul_array_len (prefixed); ++i)
+    {
+	printf ("%d\n", prefixed->data[i]);
+    }
+
+    return 0;
+}