[PATCH] MPI helper of addition one limb, Least Leak Intended

[NIIBE Yutaka]

Hello,

This change introduces a function _gcry_mpih_add_1_lli for one limb
addition with least leak.

diff --git a/mpi/mpi-inline.h b/mpi/mpi-inline.h
index 090e8a94..6954affb 100644
--- a/mpi/mpi-inline.h
+++ b/mpi/mpi-inline.h
@@ -68,6 +68,28 @@ _gcry_mpih_add_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
 }
 
 
+/* Do same calculation as _gcry_mpih_add_1 does (under the condition
+   of RES_PTR == S1_PTR), Least Leak Intended.  */
+static inline mpi_limb_t
+_gcry_mpih_add_1_lli (mpi_ptr_t s1_ptr, mpi_size_t s1_size, mpi_limb_t s2_limb)
+{
+  mpi_limb_t x;
+  mpi_limb_t cy;
+
+  x = *s1_ptr;
+  s2_limb += x;
+  *s1_ptr++ = s2_limb;
+  cy = (s2_limb < x);
+  while ( --s1_size )
+    {
+      x = *s1_ptr + cy;
+      *s1_ptr++ = x;
+      cy = mpih_limb_is_zero (x) & mpih_limb_is_not_zero (cy);
+    }
+
+  return cy;
+}
+
 
 G10_MPI_INLINE_DECL mpi_limb_t
 _gcry_mpih_add(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
--