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[loong64] Replace broken big integer arithmetic implementations
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The slightly incomprehensible LoongArch64 implementation for
bigint_subtract() is observed to produce incorrect results for some
input values.

Replace the suspicious LoongArch64 implementations of bigint_add(),
bigint_subtract(), bigint_rol() and bigint_ror(), and add a test case
for a subtraction that was producing an incorrect result with the
previous implementation.

Signed-off-by: Michael Brown <[email protected]>
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@mcb30
mcb30 committed Jan 19, 2024
1 parent bac13ba commit 908174e
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Showing 2 changed files with 115 additions and 78 deletions.
184 changes: 106 additions & 78 deletions src/arch/loong64/include/bits/bigint.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -53,34 +53,37 @@ bigint_add_raw ( const uint64_t *addend0, uint64_t *value0,
uint64_t *discard_value;
uint64_t discard_addend_i;
uint64_t discard_value_i;
uint64_t discard_carry;
uint64_t discard_temp;
unsigned int discard_size;
__asm__ __volatile__ ( "move $t0, $zero\n"
"1:\n\t"
"ld.d %3, %0, 0\n\t"
"addi.d %0, %0, 8\n\t"
"ld.d %4, %1, 0\n\t"

"add.d %4, %4, $t0\n\t"
"sltu $t0, %4, $t0\n\t"

"add.d %4, %4, %3\n\t"
"sltu $t1, %4, %3\n\t"

"or $t0, $t0, $t1\n\t"
"st.d %4, %1, 0\n\t"
__asm__ __volatile__ ( "\n1:\n\t"
/* Load addend[i] and value[i] */
"ld.d %3, %0, 0\n\t"
"ld.d %4, %1, 0\n\t"
/* Add carry flag and addend */
"add.d %4, %4, %5\n\t"
"sltu %6, %4, %5\n\t"
"add.d %4, %4, %3\n\t"
"sltu %5, %4, %3\n\t"
"or %5, %5, %6\n\t"
/* Store value[i] */
"st.d %4, %1, 0\n\t"
/* Loop */
"addi.d %0, %0, 8\n\t"
"addi.d %1, %1, 8\n\t"
"addi.w %2, %2, -1\n\t"
"bnez %2, 1b"
"bnez %2, 1b\n\t"
: "=r" ( discard_addend ),
"=r" ( discard_value ),
"=r" ( discard_size ),
"=r" ( discard_addend_i ),
"=r" ( discard_value_i ),
"=r" ( discard_carry ),
"=r" ( discard_temp ),
"+m" ( *value )
: "0" ( addend0 ),
"1" ( value0 ),
"2" ( size )
: "t0", "t1" );
: "0" ( addend0 ), "1" ( value0 ),
"2" ( size ), "5" ( 0 ) );
}

/**
Expand All @@ -93,35 +96,43 @@ bigint_add_raw ( const uint64_t *addend0, uint64_t *value0,
static inline __attribute__ (( always_inline )) void
bigint_subtract_raw ( const uint64_t *subtrahend0, uint64_t *value0,
unsigned int size ) {
bigint_t ( size ) __attribute__ (( may_alias )) *value =
( ( void * ) value0 );
uint64_t *discard_subtrahend;
uint64_t *discard_value;
uint64_t discard_subtrahend_i;
uint64_t discard_value_i;
uint64_t discard_carry;
uint64_t discard_temp;
unsigned int discard_size;
unsigned int flag = 0;

discard_subtrahend = (uint64_t*) subtrahend0;
discard_value = value0;
discard_size = size;

do {
discard_subtrahend_i = *discard_subtrahend;
discard_subtrahend++;
discard_value_i = *discard_value;

discard_value_i = discard_value_i - discard_subtrahend_i - flag;

if ( *discard_value < (discard_subtrahend_i + flag)) {
flag = 1;
} else {
flag = 0;
}

*discard_value = discard_value_i;

discard_value++;
discard_size -= 1;
} while (discard_size != 0);
__asm__ __volatile__ ( "\n1:\n\t"
/* Load subtrahend[i] and value[i] */
"ld.d %3, %0, 0\n\t"
"ld.d %4, %1, 0\n\t"
/* Subtract carry flag and subtrahend */
"sltu %6, %4, %5\n\t"
"sub.d %4, %4, %5\n\t"
"sltu %5, %4, %3\n\t"
"sub.d %4, %4, %3\n\t"
"or %5, %5, %6\n\t"
/* Store value[i] */
"st.d %4, %1, 0\n\t"
/* Loop */
"addi.d %0, %0, 8\n\t"
"addi.d %1, %1, 8\n\t"
"addi.w %2, %2, -1\n\t"
"bnez %2, 1b\n\t"
: "=r" ( discard_subtrahend ),
"=r" ( discard_value ),
"=r" ( discard_size ),
"=r" ( discard_subtrahend_i ),
"=r" ( discard_value_i ),
"=r" ( discard_carry ),
"=r" ( discard_temp ),
"+m" ( *value )
: "0" ( subtrahend0 ), "1" ( value0 ),
"2" ( size ), "5" ( 0 ) );
}

/**
Expand All @@ -132,30 +143,37 @@ bigint_subtract_raw ( const uint64_t *subtrahend0, uint64_t *value0,
*/
static inline __attribute__ (( always_inline )) void
bigint_rol_raw ( uint64_t *value0, unsigned int size ) {
bigint_t ( size ) __attribute__ (( may_alias )) *value =
( ( void * ) value0 );
uint64_t *discard_value;
uint64_t discard_value_i;
uint64_t discard_carry;
uint64_t discard_temp;
unsigned int discard_size;
uint64_t current_value_i;
unsigned int flag = 0;

discard_value = value0;
discard_size = size;
do {
discard_value_i = *discard_value;
current_value_i = discard_value_i;

discard_value_i += discard_value_i + flag;

if (discard_value_i < current_value_i) {
flag = 1;
} else {
flag = 0;
}

*discard_value = discard_value_i;
discard_value++;
discard_size -= 1;
} while ( discard_size != 0 );
__asm__ __volatile__ ( "\n1:\n\t"
/* Load value[i] */
"ld.d %2, %0, 0\n\t"
/* Shift left */
"rotri.d %2, %2, 63\n\t"
"andi %4, %2, 1\n\t"
"xor %2, %2, %4\n\t"
"or %2, %2, %3\n\t"
"move %3, %4\n\t"
/* Store value[i] */
"st.d %2, %0, 0\n\t"
/* Loop */
"addi.d %0, %0, 8\n\t"
"addi.w %1, %1, -1\n\t"
"bnez %1, 1b\n\t"
: "=r" ( discard_value ),
"=r" ( discard_size ),
"=r" ( discard_value_i ),
"=r" ( discard_carry ),
"=r" ( discard_temp ),
"+m" ( *value )
: "0" ( value0 ), "1" ( size ), "3" ( 0 )
: "cc" );
}

/**
Expand All @@ -166,27 +184,37 @@ bigint_rol_raw ( uint64_t *value0, unsigned int size ) {
*/
static inline __attribute__ (( always_inline )) void
bigint_ror_raw ( uint64_t *value0, unsigned int size ) {
bigint_t ( size ) __attribute__ (( may_alias )) *value =
( ( void * ) value0 );
uint64_t *discard_value;
uint64_t discard_value_i;
uint64_t discard_value_j;
uint64_t discard_carry;
uint64_t discard_temp;
unsigned int discard_size;

discard_value = value0;
discard_size = size;

discard_value_j = 0;

do {
discard_size -= 1;

discard_value_i = *(discard_value + discard_size);

discard_value_j = (discard_value_j << 63) | (discard_value_i >> 1);

*(discard_value + discard_size) = discard_value_j;

discard_value_j = discard_value_i;
} while ( discard_size > 0 );
__asm__ __volatile__ ( "\n1:\n\t"
/* Load value[i] */
"ld.d %2, %0, -8\n\t"
/* Shift right */
"andi %4, %2, 1\n\t"
"xor %2, %2, %4\n\t"
"or %2, %2, %3\n\t"
"move %3, %4\n\t"
"rotri.d %2, %2, 1\n\t"
/* Store value[i] */
"st.d %2, %0, -8\n\t"
/* Loop */
"addi.d %0, %0, -8\n\t"
"addi.w %1, %1, -1\n\t"
"bnez %1, 1b\n\t"
: "=r" ( discard_value ),
"=r" ( discard_size ),
"=r" ( discard_value_i ),
"=r" ( discard_carry ),
"=r" ( discard_temp ),
"+m" ( *value )
: "0" ( value0 + size ), "1" ( size ), "3" ( 0 )
: "cc" );
}

/**
Expand Down
9 changes: 9 additions & 0 deletions src/tests/bigint_test.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -714,6 +714,15 @@ static void bigint_test_exec ( void ) {
bigint_subtract_ok ( BIGINT ( 0xbb, 0x77, 0x32, 0x5a ),
BIGINT ( 0x5a, 0xd5, 0xfe, 0x28 ),
BIGINT ( 0x9f, 0x5e, 0xcb, 0xce ) );
bigint_subtract_ok ( BIGINT ( 0x00, 0x00, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff ),
BIGINT ( 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x2a ),
BIGINT ( 0xff, 0xff, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
0x00, 0x00, 0x00, 0x00, 0x00, 0x2b ) );
bigint_subtract_ok ( BIGINT ( 0x7b, 0xaa, 0x16, 0xcf, 0x15, 0x87,
0xe0, 0x4f, 0x2c, 0xa3, 0xec, 0x2f,
0x46, 0xfb, 0x83, 0xc6, 0xe0, 0xee,
Expand Down

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