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40 /******* FILE MODIFIED FROM ORIGINAL 2019u1 RELEASE TO AVOID WARNINGS *********/
41 /*
42 //
43 // Purpose:
44 // Cryptography Primitive. Modular Arithmetic Engine. General Functionality
45 //
46 // Contents:
47 // gs_mont_inv()
48 //
49 */
50
51 #include "owndefs.h"
52 #include "owncp.h"
53 #include "pcpbnumisc.h"
54 #include "pcpbnuarith.h"
55 #include "gsmodstuff.h"
56 #include "pcpmask_ct.h"
57
cpPow2_ct(int bit,BNU_CHUNK_T * dst,int len)58 __INLINE BNU_CHUNK_T* cpPow2_ct(int bit, BNU_CHUNK_T* dst, int len)
59 {
60 int slot = bit/BNU_CHUNK_BITS;
61 BNU_CHUNK_T value = (BNU_CHUNK_T)1 << (bit%BNU_CHUNK_BITS);
62
63 int i;
64 len -= (int)cpIsEqu_ct(slot, len);
65 for(i=0; i<len; i++) {
66 BNU_CHUNK_T mask = cpIsEqu_ct(slot, i);
67 dst[i] = value & mask;
68 }
69
70 return dst;
71 }
72
73 /*
74 // returns r = mont(a^-1)
75 // a in desidue domain
76 // r in Montgomery domain
77 */
gs_mont_inv(BNU_CHUNK_T * pr,const BNU_CHUNK_T * pa,gsModEngine * pME,alm_inv alm_inversion)78 BNU_CHUNK_T* gs_mont_inv(BNU_CHUNK_T* pr, const BNU_CHUNK_T* pa, gsModEngine* pME, alm_inv alm_inversion)
79 {
80 int k = alm_inversion(pr, pa, pME);
81
82 if(0==k)
83 return NULL;
84
85 {
86 int mLen = MOD_LEN(pME);
87 int m = mLen*BNU_CHUNK_BITS;
88 mod_mul mon_mul = MOD_METHOD(pME)->mul;
89
90 BNU_CHUNK_T* t = gsModPoolAlloc(pME, 1);
91 //tbcd: temporary excluded: assert(NULL!=t);
92
93 if(k<=m) {
94 mon_mul(pr, pr, MOD_MNT_R2(pME), pME);
95 k += m;
96 }
97
98 //ZEXPAND_BNU(t, 0, mLen);
99 //SET_BIT(t, 2*m-k); /* t = 2^(2*m-k) */
100 cpPow2_ct(2*m-k, t, mLen);
101 mon_mul(pr, pr, t, pME);
102
103 gsModPoolFree(pME, 1);
104
105 return pr;
106 }
107 }
108