This is an implementation Content Defined Chunking based on Rabin Footprint .It is extracted from the source code of seafile project.
You can build this project by running make.
#define CDC_MIN_BLOCK_SIZE (6 * (1 << 20)) /* 6MB */
#define CDC_MAX_BLOCK_SIZE (10 * (1 << 20)) /* 10MB */
If you need the block to be larger or smaller,just change these macros in cdc.c to the value you need.