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| |
| /* |
| // |
| // Purpose: |
| // Cryptography Primitive. Modular Arithmetic Engine. General Functionality |
| // |
| // Contents: |
| // gs_inv() |
| // |
| */ |
| |
| #include "owndefs.h" |
| #include "owncp.h" |
| #include "pcpbnumisc.h" |
| #include "pcpbnuarith.h" |
| #include "gsmodstuff.h" |
| |
| //tbcd: temporary excluded: #include <assert.h> |
| |
| /* |
| // 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, 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) { |
| 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; |
| } |
| } |