[loong64] Replace broken big integer arithmetic implementations

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 <mcb30@ipxe.org>

2 files changed, 115 insertions, 78 deletions

diff --git a/src/arch/loong64/include/bits/bigint.h b/src/arch/loong64/include/bits/bigint.h
index a37ac73..bec748b 100644
--- a/src/arch/loong64/include/bits/bigint.h
+++ b/src/arch/loong64/include/bits/bigint.h
@@ -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 ) );
 }
 
 /**
@@ -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 ) );
 }
 
 /**
@@ -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" );
 }
 
 /**
@@ -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" );
 }
 
 /**
diff --git a/src/tests/bigint_test.c b/src/tests/bigint_test.c
index f09d7c7..76aca10 100644
--- a/src/tests/bigint_test.c
+++ b/src/tests/bigint_test.c
@@ -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,