tommath/bn_mp_count_bits.c

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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
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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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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
#include <tommath.h>
/* returns the number of bits in an int */
int
mp_count_bits (mp_int * a)
{
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int r;
mp_digit q;
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/* shortcut */
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if (a->used == 0) {
return 0;
}
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/* get number of digits and add that */
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r = (a->used - 1) * DIGIT_BIT;
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/* take the last digit and count the bits in it */
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q = a->dp[a->used - 1];
while (q > ((mp_digit) 0)) {
++r;
q >>= ((mp_digit) 1);
}
return r;
}