A Dramatic Improvement
Recall the signing exponent:
(define signing-exponent 447752992032402267076910172116657103267177314627974436056129069833930674788593416236170322948214322483305175278012793102392215895931470577163544613600143471679799876664686423606429437389098641670667)
With previous versions of mod-expt,
> (mod-expt 7 signing-exponent modulus)
took 10180 years. With the latest version:
> (time (mod-expt 7 signing-exponent modulus))
cpu time: 16 real time: 38 gc time: 0
480035845964198162695390316681675930971456410079031402406756095511842878159233308075425733350601517651799075703860544976987140327389318592927018823188539796676610861096122316733992286199077843346650