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/*############################################################################
# Copyright 1999-2018 Intel Corporation
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
############################################################################*/
#include "owndefs.h"
#include "owncp.h"
#include "pcpbnumisc.h"
#include "pcpbnuarith.h"
#include "gsmodstuff.h"
//gres: temporary excluded: #include <assert.h>
/* almost Montgomery Inverse
//
// returns (k,r), r = (1/a)^k mod m
//
// requires buffer with size 4 * modLen
*/
int alm_mont_inv(BNU_CHUNK_T* pr, const BNU_CHUNK_T* pa, gsModEngine* pME)
{
const BNU_CHUNK_T* pm = MOD_MODULUS(pME);
int mLen = MOD_LEN(pME);
const int polLength = 4;
BNU_CHUNK_T* pBuffer = gsModPoolAlloc(pME, polLength);
BNU_CHUNK_T* pu = pBuffer;
BNU_CHUNK_T* ps = pu+mLen;
BNU_CHUNK_T* pv = ps+mLen;
BNU_CHUNK_T* pt = pv+mLen;
int k = 0;
BNU_CHUNK_T ext = 0;
//gres: temporary excluded: assert(NULL!=pBuffer);
// u=modulus, v=a, t=0, s=1
COPY_BNU(pu, pm, mLen);
ZEXPAND_BNU(ps, 0, mLen); ps[0] = 1;
COPY_BNU(pv, pa, mLen);
ZEXPAND_BNU(pt, 0, mLen);
while(!cpEqu_BNU_CHUNK(pv, mLen, 0)) { // while(v>0) {
if(0==(pu[0]&1)) { // if(isEven(u)) {
cpLSR_BNU(pu, pu, mLen, 1); // u = u/2;
cpAdd_BNU(ps, ps, ps, mLen); // s = 2*s;
} // }
else if(0==(pv[0]&1)) { // else if(isEven(v)) {
cpLSR_BNU(pv, pv, mLen, 1); // v = v/2;
/*ext +=*/ cpAdd_BNU(pt, pt, pt, mLen); // t = 2*t;
} // }
else {
int cmpRes = cpCmp_BNU(pu, mLen, pv, mLen);
if(cmpRes>0) { // else if (u>v) {
cpSub_BNU(pu, pu, pv, mLen); // u = (u-v);
cpLSR_BNU(pu, pu, mLen, 1); // u = u/2;
/*ext +=*/ cpAdd_BNU(pt, pt, ps, mLen); // t = t+s;
cpAdd_BNU(ps, ps, ps, mLen); // s = 2*s;
} // }
else { // else if(v>=u) {
cpSub_BNU(pv, pv, pu, mLen); // v = (v-u);
cpLSR_BNU(pv, pv, mLen, 1); // v = v/2;
cpAdd_BNU(ps, ps, pt, mLen); // s = s+t;
ext += cpAdd_BNU(pt, pt, pt, mLen); // t = 2*t;
} // }
}
k++; // k += 1;
} // }
// test
if(1!=cpEqu_BNU_CHUNK(pu, mLen, 1)) {
k = 0; /* inversion not found */
}
else {
ext -= cpSub_BNU(pr, pt, pm, mLen); // if(t>mod) r = t-mod;
cpMaskMove_gs(pr, pt, mLen, cpIsNonZero(ext)); // else r = t;
cpSub_BNU(pr, pm, pr, mLen); // return r= (mod - r) and k
}
gsModPoolFree(pME, polLength);
return k;
}
/*
// 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)
{
int k = alm_mont_inv(pr, pa, pME);
if(0==k)
pr = NULL;
else {
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);
//gres: 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) */
mon_mul(pr, pr, t, pME);
gsModPoolFree(pME, 1);
}
return pr;
}
/*
// 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)
{
int k = alm_mont_inv(pr, pa, pME);
if(0==k)
pr = NULL;
else {
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);
//gres: 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;
}
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