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Backport of "ct: Use volatile "trick" in all fe/scalar cmov implementations" #224

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Apr 11, 2023
Merged

Backport of "ct: Use volatile "trick" in all fe/scalar cmov implementations" #224

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6 changes: 4 additions & 2 deletions src/field_10x26_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1132,8 +1132,9 @@ static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_fe *a) {

static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
uint32_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->n, sizeof(r->n));
mask0 = flag + ~((uint32_t)0);
mask0 = vflag + ~((uint32_t)0);
mask1 = ~mask0;
r->n[0] = (r->n[0] & mask0) | (a->n[0] & mask1);
r->n[1] = (r->n[1] & mask0) | (a->n[1] & mask1);
Expand Down Expand Up @@ -1231,8 +1232,9 @@ static SECP256K1_INLINE void secp256k1_fe_half(secp256k1_fe *r) {

static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r, const secp256k1_fe_storage *a, int flag) {
uint32_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->n, sizeof(r->n));
mask0 = flag + ~((uint32_t)0);
mask0 = vflag + ~((uint32_t)0);
mask1 = ~mask0;
r->n[0] = (r->n[0] & mask0) | (a->n[0] & mask1);
r->n[1] = (r->n[1] & mask0) | (a->n[1] & mask1);
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6 changes: 4 additions & 2 deletions src/field_5x52_impl.h
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Expand Up @@ -476,8 +476,9 @@ static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_fe *a) {

static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_fe *a, int flag) {
uint64_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->n, sizeof(r->n));
mask0 = flag + ~((uint64_t)0);
mask0 = vflag + ~((uint64_t)0);
mask1 = ~mask0;
r->n[0] = (r->n[0] & mask0) | (a->n[0] & mask1);
r->n[1] = (r->n[1] & mask0) | (a->n[1] & mask1);
Expand Down Expand Up @@ -559,8 +560,9 @@ static SECP256K1_INLINE void secp256k1_fe_half(secp256k1_fe *r) {

static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r, const secp256k1_fe_storage *a, int flag) {
uint64_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->n, sizeof(r->n));
mask0 = flag + ~((uint64_t)0);
mask0 = vflag + ~((uint64_t)0);
mask1 = ~mask0;
r->n[0] = (r->n[0] & mask0) | (a->n[0] & mask1);
r->n[1] = (r->n[1] & mask0) | (a->n[1] & mask1);
Expand Down
3 changes: 2 additions & 1 deletion src/scalar_4x64_impl.h
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Expand Up @@ -958,8 +958,9 @@ SECP256K1_INLINE static void secp256k1_scalar_mul_shift_var(secp256k1_scalar *r,

static SECP256K1_INLINE void secp256k1_scalar_cmov(secp256k1_scalar *r, const secp256k1_scalar *a, int flag) {
uint64_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->d, sizeof(r->d));
mask0 = flag + ~((uint64_t)0);
mask0 = vflag + ~((uint64_t)0);
mask1 = ~mask0;
r->d[0] = (r->d[0] & mask0) | (a->d[0] & mask1);
r->d[1] = (r->d[1] & mask0) | (a->d[1] & mask1);
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3 changes: 2 additions & 1 deletion src/scalar_8x32_impl.h
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Expand Up @@ -733,8 +733,9 @@ SECP256K1_INLINE static void secp256k1_scalar_mul_shift_var(secp256k1_scalar *r,

static SECP256K1_INLINE void secp256k1_scalar_cmov(secp256k1_scalar *r, const secp256k1_scalar *a, int flag) {
uint32_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r->d, sizeof(r->d));
mask0 = flag + ~((uint32_t)0);
mask0 = vflag + ~((uint32_t)0);
mask1 = ~mask0;
r->d[0] = (r->d[0] & mask0) | (a->d[0] & mask1);
r->d[1] = (r->d[1] & mask0) | (a->d[1] & mask1);
Expand Down
3 changes: 2 additions & 1 deletion src/scalar_low_impl.h
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Expand Up @@ -120,8 +120,9 @@ SECP256K1_INLINE static int secp256k1_scalar_eq(const secp256k1_scalar *a, const

static SECP256K1_INLINE void secp256k1_scalar_cmov(secp256k1_scalar *r, const secp256k1_scalar *a, int flag) {
uint32_t mask0, mask1;
volatile int vflag = flag;
VG_CHECK_VERIFY(r, sizeof(*r));
mask0 = flag + ~((uint32_t)0);
mask0 = vflag + ~((uint32_t)0);
mask1 = ~mask0;
*r = (*r & mask0) | (*a & mask1);
}
Expand Down