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/* 
// 
//  Purpose:
//     Cryptography Primitive. Modular Arithmetic Engine. General Functionality
// 
//  Contents:
//        gs_inv()
//
*/

#include "owndefs.h"
#include "owncp.h"
#include "pcpbnumisc.h"
#include "pcpbnuarith.h"
#include "gsmodstuff.h"

//tbcd: temporary excluded: #include <assert.h>

/*
// returns r =1/a
//    a in desidue domain
//    r in desidue domain
*/
BNU_CHUNK_T* gs_inv(BNU_CHUNK_T* pr, const BNU_CHUNK_T* pa, gsModEngine* pME, alm_inv alm_inversion)
{
   int k = alm_inversion(pr, pa, pME);

   if(0==k)
      return NULL;

   {
      int mLen = MOD_LEN(pME);
      int m = mLen*BNU_CHUNK_BITS;
      mod_mul mon_mul = MOD_METHOD(pME)->mul;

      BNU_CHUNK_T* t = gsModPoolAlloc(pME, 1);
      //tbcd: temporary excluded: assert(NULL!=t);

      if(k>m) {
         ZEXPAND_BNU(t, 0, mLen);
         t[0] = 1;
         mon_mul(pr, pr, t, pME);
         k -= m;
      }
      ZEXPAND_BNU(t, 0, mLen);
      SET_BIT(t, m-k); /* t = 2^(m-k) */
      mon_mul(pr, pr, t, pME);

      gsModPoolFree(pME, 1);

      return pr;
   }
}