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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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36
src/arch/riscv/include/bits/bigint.h
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@@ -43,8 +43,9 @@ bigint_init_raw ( unsigned long *value0, unsigned int size,
* @v addend0 Element 0 of big integer to add
* @v value0 Element 0 of big integer to be added to
* @v size Number of elements
* @ret carry Carry out
*/
static inline __attribute__ (( always_inline )) void
static inline __attribute__ (( always_inline )) int
bigint_add_raw ( const unsigned long *addend0, unsigned long *value0,
unsigned int size ) {
bigint_t ( size ) __attribute__ (( may_alias )) *value =
@@ -54,19 +55,19 @@ bigint_add_raw ( const unsigned long *addend0, unsigned long *value0,
unsigned long *discard_value;
unsigned long discard_addend_i;
unsigned long discard_value_i;
unsigned long discard_carry;
unsigned long discard_temp;
unsigned long carry;
__asm__ __volatile__ ( "\n1:\n\t"
/* Load addend[i] and value[i] */
LOADN " %2, (%0)\n\t"
LOADN " %3, (%1)\n\t"
/* Add carry flag and addend */
"add %3, %3, %4\n\t"
"sltu %5, %3, %4\n\t"
"add %3, %3, %5\n\t"
"sltu %4, %3, %5\n\t"
"add %3, %3, %2\n\t"
"sltu %4, %3, %2\n\t"
"or %4, %4, %5\n\t"
"sltu %5, %3, %2\n\t"
"or %5, %4, %5\n\t"
/* Store value[i] */
STOREN " %3, (%1)\n\t"
/* Loop */
@@ -77,12 +78,13 @@ bigint_add_raw ( const unsigned long *addend0, unsigned long *value0,
"=&r" ( discard_value ),
"=&r" ( discard_addend_i ),
"=&r" ( discard_value_i ),
"=&r" ( discard_carry ),
"=&r" ( discard_temp ),
"=&r" ( carry ),
"+m" ( *value )
: "r" ( valueN ),
"i" ( sizeof ( unsigned long ) ),
"0" ( addend0 ), "1" ( value0 ), "4" ( 0 ) );
"0" ( addend0 ), "1" ( value0 ), "5" ( 0 ) );
return carry;
}
/**
@@ -91,8 +93,9 @@ bigint_add_raw ( const unsigned long *addend0, unsigned long *value0,
* @v subtrahend0 Element 0 of big integer to subtract
* @v value0 Element 0 of big integer to be subtracted from
* @v size Number of elements
* @ret borrow Borrow out
*/
static inline __attribute__ (( always_inline )) void
static inline __attribute__ (( always_inline )) int
bigint_subtract_raw ( const unsigned long *subtrahend0, unsigned long *value0,
unsigned int size ) {
bigint_t ( size ) __attribute__ (( may_alias )) *value =
@@ -102,19 +105,19 @@ bigint_subtract_raw ( const unsigned long *subtrahend0, unsigned long *value0,
unsigned long *discard_value;
unsigned long discard_subtrahend_i;
unsigned long discard_value_i;
unsigned long discard_carry;
unsigned long discard_temp;
unsigned long borrow;
__asm__ __volatile__ ( "\n1:\n\t"
/* Load subtrahend[i] and value[i] */
LOADN " %2, (%0)\n\t"
LOADN " %3, (%1)\n\t"
/* Subtract carry flag and subtrahend */
"sltu %5, %3, %4\n\t"
"sub %3, %3, %4\n\t"
"sltu %4, %3, %2\n\t"
"sltu %4, %3, %5\n\t"
"sub %3, %3, %5\n\t"
"sltu %5, %3, %2\n\t"
"sub %3, %3, %2\n\t"
"or %4, %4, %5\n\t"
"or %5, %5, %4\n\t"
/* Store value[i] */
STOREN " %3, (%1)\n\t"
/* Loop */
@@ -125,13 +128,14 @@ bigint_subtract_raw ( const unsigned long *subtrahend0, unsigned long *value0,
"=&r" ( discard_value ),
"=&r" ( discard_subtrahend_i ),
"=&r" ( discard_value_i ),
"=&r" ( discard_carry ),
"=&r" ( discard_temp ),
"=&r" ( borrow ),
"+m" ( *value )
: "r" ( valueN ),
"i" ( sizeof ( unsigned long ) ),
"0" ( subtrahend0 ), "1" ( value0 ),
"4" ( 0 ) );
"5" ( 0 ) );
return borrow;
}
/**