Fix some errors in brainpool rfc generation (4/7 RFC curves pass).

2 files changed, 26 insertions, 9 deletions

diff --git a/src/gen/gens.c b/src/gen/gens.c
index 2cffbc4..e2c624e 100644
--- a/src/gen/gens.c
+++ b/src/gen/gens.c
@@ -40,16 +40,25 @@ GENERATOR(gens_gen_one) {
 
 CHECK(gens_check_anomalous) {
 	if (cfg->field == FIELD_BINARY) return 1;
-	pari_sp ltop = avma;
 	for (size_t i = 0; i < curve->ngens; ++i) {
 		if (mpcmp(curve->field, curve->generators[i]->order) == 0) {
-			avma = ltop;
 			return -5;
 		}
 	}
 	return 1;
 }
 
+GEN gens_get_embedding(GEN prime, GEN order) {
+	pari_sp ltop = avma;
+	GEN power = gen_1;
+	GEN pm;
+	do {
+		power = mulii(power, prime);
+		pm = subii(power, gen_1);
+	} while (!dvdii(pm, order));
+	return gerepilecopy(ltop, power);
+}
+
 CHECK(gens_check_embedding) {
 	HAS_ARG(args);
 	if (cfg->field == FIELD_BINARY) return 1;
@@ -59,13 +68,8 @@ CHECK(gens_check_embedding) {
 	GEN mind = strtoi(min_degree);
 
 	for (size_t i = 0; i < curve->ngens; ++i) {
-		GEN power = gen_0;
-		GEN pm;
-		do {
-			power = addii(power, gen_1);
-			GEN ppow = powii(curve->field, power);
-			pm = subii(ppow, gen_1);
-		} while (!dvdii(pm, curve->generators[i]->order));
+		GEN power =
+		    gens_get_embedding(curve->field, curve->generators[i]->order);
 
 		if (mpcmp(power, mind) <= 0) {
 			avma = ltop;
diff --git a/src/gen/gens.h b/src/gen/gens.h
index 18c9815..11b349b 100644
--- a/src/gen/gens.h
+++ b/src/gen/gens.h
@@ -30,6 +30,7 @@ GENERATOR(gens_gen_any);
 GENERATOR(gens_gen_one);
 
 /**
+ * CHECK(check_f)
  *
  * @param curve
  * @param args
@@ -39,6 +40,18 @@ GENERATOR(gens_gen_one);
 CHECK(gens_check_anomalous);
 
 /**
+ * @brief Get the embedding degree of a subgroup of <code>order</code> in a
+ * power of F_prime.
+ *
+ * @param prime The order of the base field.
+ * @param order The order of the subgroup generator (in the curve group).
+ * @return The embedding degree 't' such that <code>order</code> divides
+ * 'prime^t - 1'.
+ */
+GEN gens_get_embedding(GEN prime, GEN order);
+
+/**
+ * CHECK(check_f)
  *
  * @param curve
  * @param args