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/******* FILE MODIFIED FROM ORIGINAL 2019u1 RELEASE TO AVOID WARNINGS *********/
/* 
// 
//  Purpose:
//     Cryptography Primitive. Modular Arithmetic Engine. General Functionality
// 
//  Contents:
//        gs_mont_inv()
//
*/

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

__INLINE BNU_CHUNK_T* cpPow2_ct(int bit, BNU_CHUNK_T* dst, int len)
{
   int slot = bit/BNU_CHUNK_BITS;
   BNU_CHUNK_T value = (BNU_CHUNK_T)1 << (bit%BNU_CHUNK_BITS);

   int i;
   len -= (int)cpIsEqu_ct(slot, len);
   for(i=0; i<len; i++) {
      BNU_CHUNK_T mask = cpIsEqu_ct(slot, i);
      dst[i] = value & mask;
   }

   return dst;
}

/*
// returns r = mont(a^-1)
//    a in desidue domain
//    r in Montgomery domain
*/
BNU_CHUNK_T* gs_mont_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) {
         mon_mul(pr, pr, MOD_MNT_R2(pME), pME);
         k += m;
      }

      //ZEXPAND_BNU(t, 0, mLen);
      //SET_BIT(t, 2*m-k); /* t = 2^(2*m-k) */
      cpPow2_ct(2*m-k, t, mLen);
      mon_mul(pr, pr, t, pME);

      gsModPoolFree(pME, 1);

      return pr;
   }
}