1 files changed, 60 insertions, 0 deletions
diff --git a/third_party/cachunker/src/cachunker.h b/third_party/cachunker/src/cachunker.h
new file mode 100644
index 0000000..a3714a8
--- /dev/null
+++ b/third_party/cachunker/src/cachunker.h
@@ -0,0 +1,60 @@
+/* SPDX-FileCopyrightText: Lennart Poettering <lennart@poettering.net> */
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#ifndef foochunkerhfoo
+#define foochunkerhfoo
+
+#include <inttypes.h>
+#include <sys/types.h>
+#include <stdbool.h>
+
+/* The default average chunk size */
+#define CA_CHUNK_SIZE_AVG_DEFAULT ((size_t) (64U*1024U))
+
+/* Our checksum window size */
+#define CA_CHUNKER_WINDOW_SIZE 48
+
+/* The chunk cut discriminator. In order to get an average chunk size of avg, we cut whenever for a hash value "h" at
+ * byte "i" given the descriminator "d(avg)": h(i) mod d(avg) == d(avg) - 1. Note that the discriminator
+ * calculated like this only yields correct results as long as the minimal chunk size is picked as avg/4, and the
+ * maximum chunk size as avg*4. If they are picked differently the result might be skewed into either direction. */
+#define CA_CHUNKER_DISCRIMINATOR_FROM_AVG(avg) ((size_t) (avg / (-1.42888852e-7 * avg + 1.33237515)))
+
+typedef struct CaChunker {
+        uint32_t h;
+
+        size_t window_size;
+        size_t chunk_size;
+
+        size_t chunk_size_min;
+        size_t chunk_size_max;
+        size_t chunk_size_avg;
+
+        size_t discriminator;
+
+        uint8_t window[CA_CHUNKER_WINDOW_SIZE];
+} CaChunker;
+
+/* The default initializer for the chunker. We pick an average chunk size equivalent to 64K */
+#define CA_CHUNKER_INIT                                                                        \
+        {                                                                                      \
+                .chunk_size_min = CA_CHUNK_SIZE_AVG_DEFAULT/4,                                 \
+                .chunk_size_avg = CA_CHUNK_SIZE_AVG_DEFAULT,                                   \
+                .chunk_size_max = CA_CHUNK_SIZE_AVG_DEFAULT*4,                                 \
+                .discriminator = CA_CHUNKER_DISCRIMINATOR_FROM_AVG(CA_CHUNK_SIZE_AVG_DEFAULT), \
+        }
+
+extern CaChunker ca_chunker_init;
+
+/* Set the min/avg/max chunk size. Each parameter may be 0, in which case a default is used. */
+int ca_chunker_set_size(CaChunker *c, size_t min_size, size_t avg_size, size_t max_size);
+
+/* Scans the specified data for a chunk border. Returns (size_t) -1 if none was found (and the function should be
+ * called with more data later on), or another value indicating the position of a border. */
+size_t ca_chunker_scan(CaChunker *c, const void* p, size_t n);
+
+/* Low-level buzhash functions. Only exported for testing purposes. */
+uint32_t ca_chunker_start(CaChunker *c, const void *p, size_t n);
+uint32_t ca_chunker_roll(CaChunker *c, uint8_t pop_byte, uint8_t push_byte);
+
+#endif