Add diff-delta code from git.git

src/delta.h

+/*
+ * diff-delta code taken from git.git. See diff-delta.c for details.
+ *
+ */
+#ifndef INCLUDE_git_delta_h__
+#define INCLUDE_git_delta_h__
+
+#include "common.h"
+
+/* opaque object for delta index */
+struct git_delta_index;
+
+/*
+ * create_delta_index: compute index data from given buffer
+ *
+ * This returns a pointer to a struct delta_index that should be passed to
+ * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
+ * is returned on failure.  The given buffer must not be freed nor altered
+ * before free_delta_index() is called.  The returned pointer must be freed
+ * using free_delta_index().
+ */
+extern struct git_delta_index *
+git_delta_create_index(const void *buf, unsigned long bufsize);
+
+/*
+ * free_delta_index: free the index created by create_delta_index()
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
+ */
+extern void git_delta_free_index(struct git_delta_index *index);
+
+/*
+ * sizeof_delta_index: returns memory usage of delta index
+ *
+ * Given pointer must be what create_delta_index() returned, or NULL.
+ */
+extern unsigned long git_delta_sizeof_index(struct git_delta_index *index);
+
+/*
+ * create_delta: create a delta from given index for the given buffer
+ *
+ * This function may be called multiple times with different buffers using
+ * the same delta_index pointer.  If max_delta_size is non-zero and the
+ * resulting delta is to be larger than max_delta_size then NULL is returned.
+ * On success, a non-NULL pointer to the buffer with the delta data is
+ * returned and *delta_size is updated with its size.  The returned buffer
+ * must be freed by the caller.
+ */
+extern void *
+git_delta_create(const struct git_delta_index *index,
+		 const void *buf, unsigned long bufsize,
+		 unsigned long *delta_size,
+		 unsigned long max_delta_size);
+
+/*
+ * diff_delta: create a delta from source buffer to target buffer
+ *
+ * If max_delta_size is non-zero and the resulting delta is to be larger
+ * than max_delta_size then NULL is returned.  On success, a non-NULL
+ * pointer to the buffer with the delta data is returned and *delta_size is
+ * updated with its size.  The returned buffer must be freed by the caller.
+ */
+GIT_INLINE(void *)
+git_delta(const void *src_buf, unsigned long src_bufsize,
+	  const void *trg_buf, unsigned long trg_bufsize,
+	  unsigned long *delta_size, unsigned long max_delta_size)
+{
+	struct git_delta_index *index = git_delta_create_index(src_buf, src_bufsize);
+	if (index) {
+		void *delta = git_delta_create(index, trg_buf, trg_bufsize,
+					       delta_size, max_delta_size);
+		git_delta_free_index(index);
+		return delta;
+	}
+	return NULL;
+}
+
+/*
+ * patch_delta: recreate target buffer given source buffer and delta data
+ *
+ * On success, a non-NULL pointer to the target buffer is returned and
+ * *trg_bufsize is updated with its size.  On failure a NULL pointer is
+ * returned.  The returned buffer must be freed by the caller.
+ */
+extern void *git_delta_patch(const void *src_buf, unsigned long src_size,
+			     const void *delta_buf, unsigned long delta_size,
+			     unsigned long *dst_size);
+
+/* the smallest possible delta size is 4 bytes */
+#define GIT_DELTA_SIZE_MIN	4
+
+/*
+ * This must be called twice on the delta data buffer, first to get the
+ * expected source buffer size, and again to get the target buffer size.
+ */
+GIT_INLINE(unsigned long)
+git_delta_get_hdr_size(const unsigned char **datap,
+		       const unsigned char *top)
+{
+	const unsigned char *data = *datap;
+	unsigned long cmd, size = 0;
+	int i = 0;
+	do {
+		cmd = *data++;
+		size |= (cmd & 0x7f) << i;
+		i += 7;
+	} while (cmd & 0x80 && data < top);
+	*datap = data;
+	return size;
+}
+
+#endif