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[PATCH 6/8] lib/mpi: mpi_read_buffer(): optimize skipping of leading zero limbs

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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>
---
 lib/mpi/mpicoder.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
index 623439e..2fd8d41 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);
 		}
 	}
-- 
2.7.2

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[PATCH 0/8] lib/mpi: bug fixes and cleanup Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 8/8] lib/mpi: mpi_read_buffer(): fix buffer overflow Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 2/8] lib/mpi: mpi_write_sgl(): fix style issue with lzero decrement Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 5/8] lib/mpi: mpi_write_sgl(): replace open coded endian conversion Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 1/8] lib/mpi: mpi_write_sgl(): fix skipping of leading zero limbs Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 4/8] lib/mpi: mpi_write_sgl(): fix out-of-bounds stack access Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 3/8] lib/mpi: mpi_write_sgl(): purge redundant pointer arithmetic Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  [PATCH 6/8] lib/mpi: mpi_read_buffer(): optimize skipping of leading zero limbs Nicolai Stange <nicstange@gmail.com> - 2016-03-17 19:10 +0100
  Re: [PATCH 0/8] lib/mpi: bug fixes and cleanup Nicolai Stange <nicstange@gmail.com> - 2016-03-20 13:50 +0100

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