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mbedtls_mpi_lt_mpi_ct: Improve documentation

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This commit is contained in:
Janos Follath 2019-10-28 12:23:18 +00:00
parent 51ed14e20f
commit a2b9a96fb8
1 changed files with 4 additions and 3 deletions
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7
library/bignum.c
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@ -961,6 +961,7 @@ int mbedtls_mpi_lt_mpi_ct( const mbedtls_mpi *X, const mbedtls_mpi *Y,
unsigned *ret ) unsigned *ret )
{ {
size_t i; size_t i;
/* The value of any of these variables is either 0 or 1 at all times. */
unsigned cond, done, sign_X, sign_Y; unsigned cond, done, sign_X, sign_Y;
if( X->n != Y->n ) if( X->n != Y->n )
@ -975,14 +976,14 @@ int mbedtls_mpi_lt_mpi_ct( const mbedtls_mpi *X, const mbedtls_mpi *Y,
/* /*
* If the signs are different, then the positive operand is the bigger. * If the signs are different, then the positive operand is the bigger.
* That is if X is negative (sign bit 1), then X < Y is true and it is false * That is if X is negative (sign_X == 1), then X < Y is true and it is
* if X is positive (sign bit 0). * false if X is positive (sign_X == 0).
*/ */
cond = ( sign_X ^ sign_Y ); cond = ( sign_X ^ sign_Y );
*ret = cond & sign_X; *ret = cond & sign_X;
/* /*
* This is a constant time function, we might have the result, but we still * This is a constant-time function. We might have the result, but we still
* need to go through the loop. Record if we have the result already. * need to go through the loop. Record if we have the result already.
*/ */
done = cond; done = cond;