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[crypto] Expose carry flag from big integer addition and subtraction

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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>
This commit is contained in:
Michael Brown
2024-11-26 12:53:01 +00:00
parent da6da6eb3b
commit 167a08f089
8 changed files with 140 additions and 85 deletions
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src/include/ipxe/bigint.h
+10 -8
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@@ -70,23 +70,25 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
*
* @v addend Big integer to add
* @v value Big integer to be added to
* @ret carry Carry out
*/
#define bigint_add( addend, value ) do { \
#define bigint_add( addend, value ) ( { \
unsigned int size = bigint_size (addend); \
bigint_add_raw ( (addend)->element, (value)->element, size ); \
} while ( 0 )
} )
/**
* Subtract big integers
*
* @v subtrahend Big integer to subtract
* @v value Big integer to be subtracted from
* @ret borrow Borrow out
*/
#define bigint_subtract( subtrahend, value ) do { \
#define bigint_subtract( subtrahend, value ) ( { \
unsigned int size = bigint_size (subtrahend); \
bigint_subtract_raw ( (subtrahend)->element, (value)->element, \
size ); \
} while ( 0 )
} )
/**
* Shift big integer left
@@ -389,10 +391,10 @@ void bigint_init_raw ( bigint_element_t *value0, unsigned int size,
const void *data, size_t len );
void bigint_done_raw ( const bigint_element_t *value0, unsigned int size,
void *out, size_t len );
void bigint_add_raw ( const bigint_element_t *addend0,
bigint_element_t *value0, unsigned int size );
void bigint_subtract_raw ( const bigint_element_t *subtrahend0,
bigint_element_t *value0, unsigned int size );
int bigint_add_raw ( const bigint_element_t *addend0,
bigint_element_t *value0, unsigned int size );
int bigint_subtract_raw ( const bigint_element_t *subtrahend0,
bigint_element_t *value0, unsigned int size );
void bigint_shl_raw ( bigint_element_t *value0, unsigned int size );
void bigint_shr_raw ( bigint_element_t *value0, unsigned int size );
int bigint_is_zero_raw ( const bigint_element_t *value0, unsigned int size );