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     40 
     41 /*
     42 //
     43 //  Purpose:
     44 //     Cryptography Primitive.
     45 //     Constant time Mask operations
     46 //
     47 //
     48 */
     49 
     50 #if !defined(_PCP_MASK_CT_H)
     51 #define _PCP_MASK_CT_H
     52 
     53 #include "owncp.h"
     54 #include "pcpbnuimpl.h"
     55 
     56 /*
     57 // The following functions test particular conditions
     58 // and returns either 0 or 0xffffffff.
     59 //
     60 // The result is suitable for boolean and masked operations.
     61 //
     62 // Inspite of operation below are using BNU_CHUNK_T operand(s) it can be applied to Ipp32u, Ipp32s, Ipp16u, Ipp16s, Ipp8u and Ipp8s too.
     63 // For example, if
     64 //    Ipp32u uns_int;
     65 //    Ipp32s sgn_int;
     66 //    Ipp8u  uns_char;
     67 //    Ipp8s  sgn_char;
     68 // then
     69 //    cpIs_msb_ct((Ipp32s)uns_int)     tests 31 bit of uns_int
     70 //    cpIs_msb_ct(        sgn_int)     tests 31 bit of sgn_int
     71 //    cpIs_msb_ct((Ipp8u)uns_char)     tests  7 bit of uns_char
     72 //    cpIs_msb_ct(       sgn_char)     tests  7 bit of sgn_char
     73 */
     74 
     75 /* tests if MSB(a)==1 */
     76 __INLINE BNU_CHUNK_T cpIsMsb_ct(BNU_CHUNK_T a)
     77 {
     78    return (BNU_CHUNK_T)0 - (a >> (sizeof(a) * 8 - 1));
     79 }
     80 
     81 /* tests if LSB(a)==1 */
     82 __INLINE BNU_CHUNK_T cpIsLsb_ct(BNU_CHUNK_T a)
     83 {
     84    return (BNU_CHUNK_T)0 - (a & 1);
     85 }
     86 
     87 /* tests if a is odd */
     88 __INLINE BNU_CHUNK_T cpIsOdd_ct(BNU_CHUNK_T a)
     89 {
     90    return cpIsLsb_ct(a);
     91 }
     92 
     93 /* tests if a is even */
     94 __INLINE BNU_CHUNK_T cpIsEven_ct(BNU_CHUNK_T a)
     95 {
     96    return ~cpIsLsb_ct(a);
     97 }
     98 
     99 /* tests if a==0 */
    100 __INLINE BNU_CHUNK_T cpIsZero_ct(BNU_CHUNK_T a)
    101 {
    102    return cpIsMsb_ct(~a & (a - 1));
    103 }
    104 
    105 /* tests if a==b */
    106 __INLINE BNU_CHUNK_T cpIsEqu_ct(BNU_CHUNK_T a, BNU_CHUNK_T b)
    107 {
    108    return cpIsZero_ct(a ^ b);
    109 }
    110 
    111 /* replace under mask: dst[] = replaceFlag? src[] : dst[] */
    112 __INLINE void cpMaskedReplace_ct(BNU_CHUNK_T* dst, const BNU_CHUNK_T* src, int len, BNU_CHUNK_T replaceMask)
    113 {
    114    BNU_CHUNK_T dstMask = ~replaceMask;
    115    int n;
    116    for(n=0; n<len; n++)
    117       dst[n] = (src[n] & replaceMask) ^  (dst[n] & dstMask);
    118 }
    119 
    120 /* copy under mask: dst[] = src1[] & mask) ^ src2[] & ~mask  */
    121 __INLINE void cpMaskedCopyBNU_ct(BNU_CHUNK_T* dst, BNU_CHUNK_T mask, const BNU_CHUNK_T* src1, const BNU_CHUNK_T* src2, int len)
    122 {
    123    int i;
    124    for(i=0; i<(len); i++)
    125       dst[i] = (src1[i] & mask) ^ (src2[i] & ~mask);
    126 }
    127 
    128 /* test if GF elmement is equal to x chunk */
    129 __INLINE BNU_CHUNK_T cpIsGFpElemEquChunk_ct(const BNU_CHUNK_T* pE, int nsE, BNU_CHUNK_T x)
    130 {
    131    int i;
    132    BNU_CHUNK_T accum = pE[0] ^ x;
    133    for (i = 1; i < nsE; i++) {
    134     accum |= pE[i];
    135    }
    136    return cpIsZero_ct(accum);
    137 }
    138 
    139 #define GFPE_IS_ZERO_CT(a,size)  cpIsGFpElemEquChunk_ct((a),(size), 0)
    140 
    141 #endif /* _PCP_MASK_CT_H */
    142