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/* 
//               Intel(R) Integrated Performance Primitives
//                   Cryptographic Primitives (ippcp)
// 
//  Contents:
//        cpMontSet()
//
*/

#include "owndefs.h"
#include "owncp.h"
#include "pcpbn.h"
#include "pcpmontgomery.h"
#include "pcptool.h"


/* Auxilirary function */
__INLINE int cpGetBitSize(Ipp32u offset, Ipp32u val)
{
    int bitSize = 32;
    if (val == 0) return 0;
    while ((val & (1 << bitSize)) == 0) bitSize--;
    return offset + bitSize;
}

/*F*
// Name: cpMontSet
//
// Purpose: Setup modulus value
//
// Returns:                   Reason:
//    ippStsBadModulusErr        (pModulus[0] & 1) == 0
//    ippStsOutOfRangeErr        ((Ipp32u)MNT_ROOM(pMont) < INTERNAL_BNU_LENGTH(len32))
//    ippStsLengthErr            len32<1
//    ippStsNoErr                no errors
//
// Parameters:
//    pModulus    pointer to the modulus buffer
//    len32       length of the  modulus (in Ipp32u chunks).
//    pMont       pointer to the context
*F*/

IppStatus cpMontSet(const Ipp32u* pModulus, cpSize len32, IppsMontState* pMont)
{
   IPP_BADARG_RET(len32<1, ippStsLengthErr);

   /* modulus is not an odd number */
   IPP_BADARG_RET((pModulus[0] & 1) == 0, ippStsBadModulusErr);
   IPP_BADARG_RET(MNT_ROOM(pMont)<(int)(INTERNAL_BNU_LENGTH(len32)), ippStsOutOfRangeErr);

   {
      const int poolLen  = MOD_MAXPOOL(MNT_ENGINE(pMont));
      int modulusBitSize = cpGetBitSize((len32 - 1) << 5, pModulus[len32-1]);

      gsModEngineInit(MNT_ENGINE(pMont), pModulus, modulusBitSize, poolLen, gsModArithMont());

      return ippStsNoErr;
   }
}