Mailing List Archive

* mpi/mpih-const-time.c (mpih_ct_limb_greater_than)
(mpih_ct_limb_less_than): New.
(_gcry_mpih_add_n_cond, _gcry_mpih_sub_n_cond, _gcry_mpih_abs_cond): Use
mpih_ct_limb_greater_than and mpih_ct_limb_less_than for comparisons.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
---
mpi/mpih-const-time.c | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c
index 4ebd072d..2300c666 100644
--- a/mpi/mpih-const-time.c
+++ b/mpi/mpih-const-time.c
@@ -23,6 +23,7 @@
#include "mpi-internal.h"
#include "g10lib.h"
#include "const-time.h"
+#include "longlong.h"

#define A_LIMB_1 ((mpi_limb_t)1)

@@ -31,6 +32,28 @@ DEFINE_CT_TYPE_GEN_MASK(limb, mpi_limb_t)
DEFINE_CT_TYPE_GEN_INV_MASK(limb, mpi_limb_t)


+/*
+ * Return 1 if X > Y and otherwise return 0.
+ */
+static mpi_limb_t
+mpih_ct_limb_greater_than (mpi_limb_t x, mpi_limb_t y)
+{
+ mpi_limb_t diff_hi, diff_lo;
+ sub_ddmmss (diff_hi, diff_lo, 0, y, 0, x);
+ return diff_hi >> (BITS_PER_MPI_LIMB - 1);
+}
+
+
+/*
+ * Return 1 if X < Y and otherwise return 0.
+ */
+static mpi_limb_t
+mpih_ct_limb_less_than (mpi_limb_t x, mpi_limb_t y)
+{
+ return mpih_ct_limb_greater_than (y, x);
+}
+
+
/*
* W = U when OP_ENABLED=1
* otherwise, W keeps old value
@@ -70,11 +93,11 @@ _gcry_mpih_add_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
{
mpi_limb_t u = up[i];
mpi_limb_t x = u + vp[i];
- mpi_limb_t cy1 = x < u;
+ mpi_limb_t cy1 = mpih_ct_limb_less_than(x, u);
mpi_limb_t cy2;

x = x + cy;
- cy2 = x < cy;
+ cy2 = mpih_ct_limb_less_than(x, cy);
cy = cy1 | cy2;
wp[i] = (u & mask2) | (x & mask1);
}
@@ -102,10 +125,10 @@ _gcry_mpih_sub_n_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_ptr_t vp,
{
mpi_limb_t u = up[i];
mpi_limb_t x = u - vp[i];
- mpi_limb_t cy1 = x > u;
+ mpi_limb_t cy1 = mpih_ct_limb_greater_than(x, u);
mpi_limb_t cy2;

- cy2 = x < cy;
+ cy2 = mpih_ct_limb_less_than(x, cy);
x = x - cy;
cy = cy1 | cy2;
wp[i] = (u & mask2) | (x & mask1);
@@ -157,7 +180,7 @@ _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize,
mpi_limb_t u = up[i];
mpi_limb_t x = ~u + cy;

- cy = (x < ~u);
+ cy = mpih_ct_limb_less_than(x, ~u);
wp[i] = (u & mask2) | (x & mask1);
}
}
--
2.40.1


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