[crypto] Eliminate temporary working space for bigint_mod_invert()

With a slight modification to the algorithm to ignore bits of the
residue that can never contribute to the result, it is possible to
reuse the as-yet uncalculated portions of the inverse to hold the
residue.  This removes the requirement for additional temporary
working space.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 5 insertions, 19 deletions

diff --git a/src/include/ipxe/bigint.h b/src/include/ipxe/bigint.h
index 330d7deec..e55c536c7 100644
--- a/src/include/ipxe/bigint.h
+++ b/src/include/ipxe/bigint.h
@@ -242,31 +242,18 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 	} while ( 0 )
 
 /**
- * Compute inverse of odd big integer modulo its own size
+ * Compute inverse of odd big integer modulo any power of two
  *
  * @v invertend		Odd big integer to be inverted
  * @v inverse		Big integer to hold result
- * @v tmp		Temporary working space
  */
-#define bigint_mod_invert( invertend, inverse, tmp ) do {		\
-	unsigned int size = bigint_size (invertend);			\
+#define bigint_mod_invert( invertend, inverse ) do {			\
+	unsigned int size = bigint_size ( invertend );			\
 	bigint_mod_invert_raw ( (invertend)->element,			\
-				(inverse)->element, size, tmp );	\
+				(inverse)->element, size );		\
 	} while ( 0 )
 
 /**
- * Calculate temporary working space required for modular inversion
- *
- * @v invertend		Odd big integer to be inverted
- * @ret len		Length of temporary working space
- */
-#define bigint_mod_invert_tmp_len( invertend ) ( {			\
-	unsigned int size = bigint_size (invertend);			\
-	sizeof ( struct {						\
-		bigint_t ( size ) temp_residue;				\
-	} ); } )
-
-/**
  * Perform modular multiplication of big integers
  *
  * @v multiplicand	Big integer to be multiplied
@@ -408,8 +395,7 @@ void bigint_multiply_raw ( const bigint_element_t *multiplicand0,
 void bigint_reduce_raw ( bigint_element_t *modulus0, bigint_element_t *value0,
 			 unsigned int size );
 void bigint_mod_invert_raw ( const bigint_element_t *invertend0,
-			     bigint_element_t *inverse0,
-			     unsigned int size, void *tmp );
+			     bigint_element_t *inverse0, unsigned int size );
 void bigint_mod_multiply_raw ( const bigint_element_t *multiplicand0,
 			       const bigint_element_t *multiplier0,
 			       const bigint_element_t *modulus0,