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Alternative cmov implementation #457

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41 changes: 17 additions & 24 deletions src/field_10x26_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,21 @@
#include "num.h"
#include "field.h"

static SECP256K1_INLINE void secp256k1_fe_cmov_limbs(uint32_t *r, const uint32_t *a, int len, int flag) {
int i;
uint32_t diff, rest, r_i;
static const uint32_t half = 0x55555555UL;
VERIFY_CHECK(flag == 0 || flag == 1);
rest = half << flag;
for (i=0; i<len; i++) {
r_i = r[i];
diff = r_i ^ a[i];
r_i ^= (diff & half);
r_i ^= (diff & rest);
r[i] = r_i;
}
}

#ifdef VERIFY
static void secp256k1_fe_verify(const secp256k1_fe *a) {
const uint32_t *d = a->n;
Expand Down Expand Up @@ -1092,19 +1107,7 @@ 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;
mask0 = flag + ~((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);
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
r->n[5] = (r->n[5] & mask0) | (a->n[5] & mask1);
r->n[6] = (r->n[6] & mask0) | (a->n[6] & mask1);
r->n[7] = (r->n[7] & mask0) | (a->n[7] & mask1);
r->n[8] = (r->n[8] & mask0) | (a->n[8] & mask1);
r->n[9] = (r->n[9] & mask0) | (a->n[9] & mask1);
secp256k1_fe_cmov_limbs(r->n, a->n, 10, flag);
#ifdef VERIFY
if (a->magnitude > r->magnitude) {
r->magnitude = a->magnitude;
Expand All @@ -1114,17 +1117,7 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_
}

static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r, const secp256k1_fe_storage *a, int flag) {
uint32_t mask0, mask1;
mask0 = flag + ~((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);
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
r->n[5] = (r->n[5] & mask0) | (a->n[5] & mask1);
r->n[6] = (r->n[6] & mask0) | (a->n[6] & mask1);
r->n[7] = (r->n[7] & mask0) | (a->n[7] & mask1);
secp256k1_fe_cmov_limbs(r->n, a->n, 8, flag);
}

static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
Expand Down
32 changes: 17 additions & 15 deletions src/field_5x52_impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,21 @@
* output.
*/

static SECP256K1_INLINE void secp256k1_fe_cmov_limbs(uint64_t *r, const uint64_t *a, int len, int flag) {
int i;
uint64_t diff, rest, r_i;
static const uint64_t half = 0x5555555555555555ULL;
VERIFY_CHECK(flag == 0 || flag == 1);
rest = half << flag;
for (i=0; i<len; i++) {
r_i = r[i];
diff = r_i ^ a[i];
r_i ^= (diff & half);
r_i ^= (diff & rest);
r[i] = r_i;
}
}

#ifdef VERIFY
static void secp256k1_fe_verify(const secp256k1_fe *a) {
const uint64_t *d = a->n;
Expand Down Expand Up @@ -445,14 +460,7 @@ 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;
mask0 = flag + ~((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);
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
secp256k1_fe_cmov_limbs(r->n, a->n, 5, flag);
#ifdef VERIFY
if (a->magnitude > r->magnitude) {
r->magnitude = a->magnitude;
Expand All @@ -462,13 +470,7 @@ static SECP256K1_INLINE void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_
}

static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r, const secp256k1_fe_storage *a, int flag) {
uint64_t mask0, mask1;
mask0 = flag + ~((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);
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
secp256k1_fe_cmov_limbs(r->n, a->n, 4, flag);
}

static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
Expand Down