Remove the unused prej allocations.

Author: roconnor-blockstream

src/ecmult_impl.h

@@ -77,10 +77,12 @@
 
 #define ECMULT_MAX_POINTS_PER_BATCH 5000000
 
-/** Fill a table 'prej' with precomputed odd multiples of a. Prej will contain
+/** Fill a table 'pre_a' with precomputed odd multiples of a. Pre_a will contain
  *  the values [1*a,3*a,...,(2*n-1)*a], so it space for n values. zr[0] will
- *  contain prej[0].z / a.z. The other zr[i] values = prej[i].z / prej[i-1].z.
- *  Prej's Z values are undefined, except for the last value.
+ *  contain pre_a[0].z / a.z. The other zr[i] values = pre_a[i].z / pre_a[i-1].z.
+ *  The a value will end up equal to pre_a[(2*n-1)].
+ *  The output pre_a array will have their z-coordinate omitted.
+ *  The omitted z-coordinate are implied by the final a value's z-coordinate and the zr array.
  */
 static void secp256k1_ecmult_odd_multiples_table(int n, secp256k1_ge *pre_a, secp256k1_fe *zr, secp256k1_gej *a) {
     secp256k1_gej d;
@@ -435,7 +437,6 @@ struct secp256k1_strauss_point_state {
 };
 
 struct secp256k1_strauss_state {
-    secp256k1_gej* prej;
     secp256k1_fe* zr;
     secp256k1_ge* pre_a;
     secp256k1_ge* pre_a_lam;
@@ -561,14 +562,12 @@ static void secp256k1_ecmult_strauss_wnaf(const secp256k1_ecmult_context *ctx, c
 }
 
 static void secp256k1_ecmult(const secp256k1_ecmult_context *ctx, secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_scalar *na, const secp256k1_scalar *ng) {
-    secp256k1_gej prej[ECMULT_TABLE_SIZE(WINDOW_A)];
     secp256k1_fe zr[ECMULT_TABLE_SIZE(WINDOW_A)];
     secp256k1_ge pre_a[ECMULT_TABLE_SIZE(WINDOW_A)];
     struct secp256k1_strauss_point_state ps[1];
     secp256k1_ge pre_a_lam[ECMULT_TABLE_SIZE(WINDOW_A)];
     struct secp256k1_strauss_state state;
 
-    state.prej = prej;
     state.zr = zr;
     state.pre_a = pre_a;
     state.pre_a_lam = pre_a_lam;
@@ -577,7 +576,7 @@ static void secp256k1_ecmult(const secp256k1_ecmult_context *ctx, secp256k1_gej
 }
 
 static size_t secp256k1_strauss_scratch_size(size_t n_points) {
-    static const size_t point_size = (2 * sizeof(secp256k1_ge) + sizeof(secp256k1_gej) + sizeof(secp256k1_fe)) * ECMULT_TABLE_SIZE(WINDOW_A) + sizeof(struct secp256k1_strauss_point_state) + sizeof(secp256k1_gej) + sizeof(secp256k1_scalar);
+    static const size_t point_size = (2 * sizeof(secp256k1_ge) + sizeof(secp256k1_fe)) * ECMULT_TABLE_SIZE(WINDOW_A) + sizeof(struct secp256k1_strauss_point_state) + sizeof(secp256k1_gej) + sizeof(secp256k1_scalar);
     return n_points*point_size;
 }
 
@@ -595,13 +594,12 @@ static int secp256k1_ecmult_strauss_batch(const secp256k1_callback* error_callba
 
     points = (secp256k1_gej*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(secp256k1_gej));
     scalars = (secp256k1_scalar*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(secp256k1_scalar));
-    state.prej = (secp256k1_gej*)secp256k1_scratch_alloc(error_callback, scratch, n_points * ECMULT_TABLE_SIZE(WINDOW_A) * sizeof(secp256k1_gej));
     state.zr = (secp256k1_fe*)secp256k1_scratch_alloc(error_callback, scratch, n_points * ECMULT_TABLE_SIZE(WINDOW_A) * sizeof(secp256k1_fe));
     state.pre_a = (secp256k1_ge*)secp256k1_scratch_alloc(error_callback, scratch, n_points * ECMULT_TABLE_SIZE(WINDOW_A) * sizeof(secp256k1_ge));
     state.pre_a_lam = (secp256k1_ge*)secp256k1_scratch_alloc(error_callback, scratch, n_points * ECMULT_TABLE_SIZE(WINDOW_A) * sizeof(secp256k1_ge));
     state.ps = (struct secp256k1_strauss_point_state*)secp256k1_scratch_alloc(error_callback, scratch, n_points * sizeof(struct secp256k1_strauss_point_state));
 
-    if (points == NULL || scalars == NULL || state.prej == NULL || state.zr == NULL || state.pre_a == NULL || state.pre_a_lam == NULL || state.ps == NULL) {
+    if (points == NULL || scalars == NULL || state.zr == NULL || state.pre_a == NULL || state.pre_a_lam == NULL || state.ps == NULL) {
         secp256k1_scratch_apply_checkpoint(error_callback, scratch, scratch_checkpoint);
         return 0;
     }