Uboot is an open-source bootloader, licensed to Ubiquiti under the GNU General Public License. Despite the terms of that license, Ubiquiti refuses to release the corresponding source code for their modified version.
Ubiquiti has distributed firmware on and for their hardware. This table provides sizes and hashes of the u-boot embedded in a subset of their firmwares. These are organized by device type and chronologically within device type, keeping common hashes together.
The hashes were computed by first extracting the u-boot. In general, the hashes will vary from what can be read using dd if=/dev/mtdblock0 because of padding out the 256k partition and trailing garbage. The extraction was made using something like this:
3a8082e126