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     40 
     41 /*
     42 //
     43 //  Purpose:
     44 //     Cryptography Primitive. Modular Arithmetic Engine. General Functionality
     45 //
     46 //  Contents:
     47 //        gs_inv()
     48 //
     49 */
     50 
     51 #include "owndefs.h"
     52 #include "owncp.h"
     53 #include "pcpbnumisc.h"
     54 #include "pcpbnuarith.h"
     55 #include "gsmodstuff.h"
     56 
     57 //tbcd: temporary excluded: #include <assert.h>
     58 
     59 /*
     60 // returns r =1/a
     61 //    a in desidue domain
     62 //    r in desidue domain
     63 */
     64 BNU_CHUNK_T* gs_inv(BNU_CHUNK_T* pr, const BNU_CHUNK_T* pa, gsModEngine* pME, alm_inv alm_inversion)
     65 {
     66    int k = alm_inversion(pr, pa, pME);
     67 
     68    if(0==k)
     69       return NULL;
     70 
     71    {
     72       int mLen = MOD_LEN(pME);
     73       int m = mLen*BNU_CHUNK_BITS;
     74       mod_mul mon_mul = MOD_METHOD(pME)->mul;
     75 
     76       BNU_CHUNK_T* t = gsModPoolAlloc(pME, 1);
     77       //tbcd: temporary excluded: assert(NULL!=t);
     78 
     79       if(k>m) {
     80          ZEXPAND_BNU(t, 0, mLen);
     81          t[0] = 1;
     82          mon_mul(pr, pr, t, pME);
     83          k -= m;
     84       }
     85       ZEXPAND_BNU(t, 0, mLen);
     86       SET_BIT(t, m-k); /* t = 2^(m-k) */
     87       mon_mul(pr, pr, t, pME);
     88 
     89       gsModPoolFree(pME, 1);
     90 
     91       return pr;
     92    }
     93 }
     94