Merge pull request #9 from benjaminion/Nashatyrev-feature/add-fr-to-uints

Add fr_to_uints() function

src/bls12_381.c

@@ -104,7 +104,7 @@ void fr_from_scalar(fr_t *out, const scalar_t *a) {
  * @param out  The field element equivalent of @p n
  * @param vals The array of 64-bit integers to be converted, little-endian ordering of the 64-bit words
  */
-void fr_from_uint64s(fr_t *out, const uint64_t *vals) {
+void fr_from_uint64s(fr_t *out, const uint64_t vals[4]) {
     blst_fr_from_uint64(out, vals);
 }
 
@@ -121,6 +121,16 @@ void fr_from_uint64(fr_t *out, uint64_t n) {
     fr_from_uint64s(out, vals);
 }
 
+/**
+ * Convert a field element to an array of four 64-bit unsigned integers.
+ *
+ * @param out  Array for returned values, little-endian ordering of the 64-bit words
+ * @param vals The field element equivalent of @p n
+ */
+void fr_to_uint64s(uint64_t out[4], const fr_t *fr) {
+    blst_uint64_from_fr(out, fr);
+}
+
 /**
  * Test whether two field elements are equal.
  *

src/bls12_381.h

@@ -104,6 +104,7 @@ bool fr_is_null(const fr_t *p);
 void fr_from_scalar(fr_t *out, const scalar_t *a);
 void fr_from_uint64s(fr_t *out, const uint64_t *vals);
 void fr_from_uint64(fr_t *out, uint64_t n);
+void fr_to_uint64s(uint64_t out[4], const fr_t* fr);
 bool fr_equal(const fr_t *aa, const fr_t *bb);
 void fr_negate(fr_t *out, const fr_t *in);
 void fr_add(fr_t *out, const fr_t *a, const fr_t *b);

src/bls12_381_test.c

@@ -110,6 +110,20 @@ void fr_div_by_zero(void) {
     TEST_CHECK(fr_is_zero(&tmp));
 }
 
+void fr_uint64s_roundtrip(void) {
+    fr_t fr;
+    uint64_t expected[4] = {1, 2, 3, 4};
+    uint64_t actual[4];
+
+    fr_from_uint64s(&fr, expected);
+    fr_to_uint64s(actual, &fr);
+
+    TEST_CHECK(expected[0] == actual[0]);
+    TEST_CHECK(expected[1] == actual[1]);
+    TEST_CHECK(expected[2] == actual[2]);
+    TEST_CHECK(expected[3] == actual[3]);
+}
+
 void p1_mul_works(void) {
     fr_t minus1;
     g1_t res;
@@ -235,6 +249,7 @@ TEST_LIST = {
     {"fr_pow_works", fr_pow_works},
     {"fr_div_works", fr_div_works},
     {"fr_div_by_zero", fr_div_by_zero},
+    {"fr_uint64s_roundtrip", fr_uint64s_roundtrip},
     {"p1_mul_works", p1_mul_works},
     {"p1_sub_works", p1_sub_works},
     {"p2_mul_works", p2_mul_works},