lib/mpi: mpi_read_buffer(): optimize skipping of leading zero limbs

Currently, if the number of leading zeros is greater than fits into a
complete limb, mpi_read_buffer() skips them by iterating over them
limb-wise.

Instead of skipping the high order zero limbs within the loop as shown
above, adjust the copying loop's bounds.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 8 insertions, 10 deletions

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 623439e4bad5..2fd8d418526c 100644
--- a/lib/mpi/mpicoder.c
+++ b/lib/mpi/mpicoder.c
@@ -184,7 +184,9 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
         p = buf;
         *nbytes = n - lzeros;
 
-        for (i = a->nlimbs - 1; i >= 0; i--) {
+        for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
+                        lzeros %= BYTES_PER_MPI_LIMB;
+                i >= 0; i--) {
                 alimb = a->d[i];
 #if BYTES_PER_MPI_LIMB == 4
                 *p++ = alimb >> 24;
@@ -205,15 +207,11 @@ int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 #endif
 
                 if (lzeros > 0) {
-                        if (lzeros >= sizeof(alimb)) {
-                                p -= sizeof(alimb);
-                        } else {
-                                mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
-                                mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
-                                                        + lzeros;
-                                *limb1 = *limb2;
-                                p -= lzeros;
-                        }
+                        mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
+                        mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
+                                + lzeros;
+                        *limb1 = *limb2;
+                        p -= lzeros;
                         lzeros -= sizeof(alimb);
                 }
         }