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[crypto] Add bigint_msb_is_set() to clarify code

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Add a dedicated bigint_msb_is_set() to reduce the amount of open
coding required in the common case of testing the sign of a two's
complement big integer.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2024-11-07 14:43:56 +00:00
parent e9a23a5b39
commit da6da6eb3b
3 changed files with 30 additions and 5 deletions
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src/crypto/x25519.c
+1 -2
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@@ -563,7 +563,6 @@ void x25519_invert ( const union x25519_oct258 *invertend,
* @v value Big integer to be subtracted from, if possible
*/
static void x25519_reduce_by ( const x25519_t *subtrahend, x25519_t *value ) {
unsigned int max_bit = ( ( 8 * sizeof ( *value ) ) - 1 );
x25519_t tmp;
/* Conditionally subtract subtrahend
@@ -573,7 +572,7 @@ static void x25519_reduce_by ( const x25519_t *subtrahend, x25519_t *value ) {
*/
bigint_copy ( value, &tmp );
bigint_subtract ( subtrahend, value );
bigint_swap ( value, &tmp, bigint_bit_is_set ( value, max_bit ) );
bigint_swap ( value, &tmp, bigint_msb_is_set ( value ) );
}
/**