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Improve documentation of mbedtls_mpi_write_string()

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Hanno Becker 2019-02-04 09:45:07 +00:00 committed by Janos Follath
parent ae499753a2
commit c1fa6cdab6
1 changed files with 14 additions and 9 deletions
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23
library/bignum.c
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@ -582,15 +582,20 @@ int mbedtls_mpi_write_string( const mbedtls_mpi *X, int radix,
if( radix < 2 || radix > 16 ) if( radix < 2 || radix > 16 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA ); return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
n = mbedtls_mpi_bitlen( X ); n = mbedtls_mpi_bitlen( X ); /* Number of bits necessary to present `n`. */
if( radix >= 4 ) n >>= 1; if( radix >= 4 ) n >>= 1; /* Number of 4-adic digits necessary to present
if( radix >= 16 ) n >>= 1; * `n`. If radix > 4, this might be a strict
/* * overapproximation of the number of
* Round up the buffer length to an even value to ensure that there is * radix-adic digits needed to present `n`. */
* enough room for hexadecimal values that can be represented in an odd if( radix >= 16 ) n >>= 1; /* Number of hexadecimal digits necessary to
* number of digits. * present `n`. */
*/
n += 3 + ( ( n + 1 ) & 1 ); n += 1; /* NULL termination */
n += 1; /* Compensate for the divisions above, which round down `n`
* in case it's not even. */
n += 1; /* Potential '-'-sign. */
n += ( n & 1 ); /* Make n even to have enough space for hexadecimal writing,
* which always uses an even number of hex-digits. */
if( buflen < n ) if( buflen < n )
{ {