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/*
//     Intel(R) Integrated Performance Primitives. Cryptography Primitives.
// 
//     Context:
//        cpMontMultiExpInitArray()
//
*/

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

/* 
//               Intel(R) Integrated Performance Primitives
//                   Cryptographic Primitives (ippcp)
// 
// 
*/
/*
// Initialize multi-exponentiation computation
//    y = x[0]^e[0] * x[1]^e[1] *...* x[numItems-1]^e[numItems-1] mod M
//
// Output:
//    - table pTbl of precomuted values pTbl[i] = x[0]^i[0] * x[1]^i[1] *...* x[numItems-1]^i[numItems-1] mod M,
//      where i[0], i[1], ..., i[numItems-1] are bits of i value;
//
// Input:
//    - array of pointers to the BNU bases x[0], x[1],...,x[numItems-1]
//    - pointer to the Montgomery engine
*/
void cpMontMultiExpInitArray(BNU_CHUNK_T* pPrecomTbl,
              const BNU_CHUNK_T** ppX, cpSize xItemBitSize,
              cpSize numItems,
              gsModEngine* pModEngine)
{
   cpSize sizeM = MOD_LEN(pModEngine);

   cpSize i, base;
   cpSize sizeX = BITS_BNU_CHUNK(xItemBitSize);

   /* buff[0] = mont(1) */
   COPY_BNU(pPrecomTbl, MOD_MNT_R(pModEngine), sizeM);
   /* buff[1] = X[0] */
   ZEXPAND_COPY_BNU(pPrecomTbl+sizeM, sizeM, ppX[0], sizeX);

   for(i=1,base=2*sizeM; i<numItems; i++,base*=2) {
      /* buf[base] = X[i] */
      ZEXPAND_COPY_BNU(pPrecomTbl+base, sizeM, ppX[i], sizeX);

      {
         int nPasses = 1;
         int step = base/2;

         int k;
         for(k=i-1; k>=0; k--) {
            const BNU_CHUNK_T* pXterm = ppX[k];

            BNU_CHUNK_T* pBufferBase = pPrecomTbl+base;
            int n;
            for(n=1; n<=nPasses; n++, pBufferBase+=2*step) {
               cpMontMul_BNU_EX(pBufferBase+step,
                                pBufferBase,      sizeM,
                                pXterm,           sizeX,
                                pModEngine);
            }

            nPasses *= 2;
            step /= 2;
         }
      }
   }
}