yes the suggestion was helpful. I've implemented the ECDSA signature verifying algorithm successfully with the BigDigits Library for multiprecision math. The performance is slower than the GMP functions (implemented in mini-gmp.c subset). Therefor I have to optimize the math functions which are written in standard c with assembly functions. Unfortunately the calling convention between C-Compiler (CW 10.2) and assembly functions I have found for this problem (using emac Hardware) is different, so if anyone has this problem too, alsp take a look at Problems with MAC and EMAC macros in ColdFire V1+