51 lines
1.2 KiB
C
51 lines
1.2 KiB
C
#include "tommath_private.h"
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#ifdef BN_MP_GET_BIT_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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/* Checks the bit at position b and returns MP_YES
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if the bit is 1, MP_NO if it is 0 and MP_VAL
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in case of error */
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int mp_get_bit(const mp_int *a, int b)
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{
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int limb;
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mp_digit bit, isset;
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if (b < 0) {
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return MP_VAL;
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}
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limb = b / DIGIT_BIT;
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/*
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* Zero is a special value with the member "used" set to zero.
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* Needs to be tested before the check for the upper boundary
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* otherwise (limb >= a->used) would be true for a = 0
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*/
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if(mp_iszero(a)) {
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return MP_NO;
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}
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if (limb >= a->used) {
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return MP_VAL;
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}
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bit = (mp_digit)1 << ((mp_digit)b % DIGIT_BIT);
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isset = a->dp[limb] & bit;
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return (isset != 0) ? MP_YES : MP_NO;
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}
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#endif
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