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| author | Michael Brown <mcb30@ipxe.org> | 2024-11-26 12:53:01 +0000 |
|---|---|---|
| committer | Michael Brown <mcb30@ipxe.org> | 2024-11-26 12:55:13 +0000 |
| commit | 167a08f08928c7e469f50d5d364287abb784e99c (patch) | |
| tree | 039a60c76e5da50dfe17cffb41c4491087c2c74f /src/crypto/x25519.c | |
| parent | da6da6eb3b83fe92002e9c8e245933498ba19a48 (diff) | |
| download | ipxe-167a08f08928c7e469f50d5d364287abb784e99c.tar.gz | |
[crypto] Expose carry flag from big integer addition and subtraction
Expose the effective carry (or borrow) out flag from big integer
addition and subtraction, and use this to elide an explicit bit test
when performing x25519 reduction.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Diffstat (limited to 'src/crypto/x25519.c')
| -rw-r--r-- | src/crypto/x25519.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/src/crypto/x25519.c b/src/crypto/x25519.c index 19f9a2c02..ab5d2e8b0 100644 --- a/src/crypto/x25519.c +++ b/src/crypto/x25519.c @@ -564,6 +564,7 @@ void x25519_invert ( const union x25519_oct258 *invertend, */ static void x25519_reduce_by ( const x25519_t *subtrahend, x25519_t *value ) { x25519_t tmp; + int underflow; /* Conditionally subtract subtrahend * @@ -571,8 +572,8 @@ static void x25519_reduce_by ( const x25519_t *subtrahend, x25519_t *value ) { * time) if the subtraction underflows. */ bigint_copy ( value, &tmp ); - bigint_subtract ( subtrahend, value ); - bigint_swap ( value, &tmp, bigint_msb_is_set ( value ) ); + underflow = bigint_subtract ( subtrahend, value ); + bigint_swap ( value, &tmp, underflow ); } /** |