Fix #309: gdImageGd2() writes wrong chunk sizes on boundaries

src/gd_gd2.c

@@ -938,8 +938,8 @@ _gdImageGd2 (gdImagePtr im, gdIOCtx * out, int cs, int fmt)
 	};
 
 	/* Work out number of chunks. */
-	ncx = im->sx / cs + 1;
-	ncy = im->sy / cs + 1;
+	ncx = (im->sx + cs - 1) / cs;
+	ncy = (im->sy + cs - 1) / cs;
 
 	/* Write the standard header. */
 	_gd2PutHeader (im, out, cs, fmt, ncx, ncy);

tests/gd2/.gitignore

@@ -1,4 +1,5 @@
 /bug_289
+/bug00309
 /gd2_empty_file
 /gd2_im2im
 /gd2_null

tests/gd2/CMakeLists.txt

@@ -1,5 +1,6 @@
 LIST(APPEND TESTS_FILES
 	bug_289
+	bug00309
 	gd2_empty_file
 	gd2_im2im
 	gd2_null

tests/gd2/Makemodule.am

@@ -1,5 +1,6 @@
 libgd_test_programs += \
 	gd2/bug_289 \
+	gd2/bug00309 \
 	gd2/gd2_empty_file \
 	gd2/php_bug_72339 \
 	gd2/gd2_read_corrupt

tests/gd2/bug00309.c

@@ -0,0 +1,37 @@
+/**
+ * Regression test for <https://github.com/libgd/libgd/issues/309>.
+ *
+ * We test that an image with 64x64 pixels reports only a single chunk in the
+ * GD2 image header when the chunk size is 64.
+ */
+
+
+#include "gd.h"
+#include "gdtest.h"
+
+
+int main()
+{
+    gdImagePtr im;
+    unsigned char *buf;
+    int size, word;
+
+    im = gdImageCreate(64, 64);
+    gdImageColorAllocate(im, 0, 0, 0);
+
+    buf = gdImageGd2Ptr(im, 64, 1, &size);
+
+    gdImageDestroy(im);
+
+    word = buf[10] << 8 | buf[11];
+    gdTestAssertMsg(word == 64, "chunk size is %d, but expected 64\n", word);
+    word = buf[14] << 8 | buf[15];
+    gdTestAssertMsg(word == 1, "x chunk count is %d, but expected 1\n", word);
+    word = buf[16] << 8 | buf[17];
+    gdTestAssertMsg(word == 1, "y chunk count is %d, but expected 1\n", word);
+    gdTestAssertMsg(size == 5145, "file size is %d, but expected 5145\n", size);
+
+    gdFree(buf);
+
+    return gdNumFailures();
+}