In view of difficulty of SHA2 hardware acceleration, a novel performance-improving scheme of SHA2 hardware accelerator is put forth with the following techniques adopted. 1) Using 4K bits Ping-Pong buffer storing padded message block, the Message Padding Unit and Hash Calculation Unit can work in parallel as two stages of two-stage pipeline. 2) In Hash Calculation Unit, computations which have no dependency on iterative computation are extracted from two folded rounds of hash transformation as pre-computation unit and can work concurrently with post-computation unit in the form of two-stage pipeline rather than pseudo-pipeline which was proposed in the previous researches. 3) 3:2/4:2 compressors without carry chain and fast adders are adopted in pre-computation unit and post-computation unit to shorten critical path greatly. The proposed scheme also supports double hash computation which directs digest result of source data to the entry of hash iteration unit to obtain final result of double hash of SHA2, improving the performance of SHA2 hardware accelerator.

Aiming at the problem that the Gauss-Newton (GN) method is sensitive to the initial information matrix in the Bundle Adjustment (BA) model, which leads to limited application scenarios, the paper proposes a novel method BFGS-GN using BFGS (Broyden-Fletcher-Goldfarb-Shanno) algorithm to improve the traditional Gauss-Newton method. When the information matrix of the Gauss-Newton method loses positive definiteness, BFGS algorithm can be used to modify the normal equations, which fundamentally eliminates the mathematical defect that the Gauss-Newton method is sensitive to initial values. Experimental results demonstrate that proposed method is robust to different types of initials. The same accuracy and the number of iterations as GN can be obtained when the initial values are good. As for bad inputs, GN-based BA method cannot work but BFGS-GN can converge to a minimum.