common/features: expose feature bitmap low-level functions.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/features.c

@@ -21,7 +21,7 @@ static const u32 our_globalfeatures[] = {
  *
  * All data fields are unsigned big-endian unless otherwise specified.
  */
-static void set_bit(u8 **ptr, u32 bit)
+void set_feature_bit(u8 **ptr, u32 bit)
 {
 	size_t len = tal_count(*ptr);
 	if (bit / 8 >= len) {
@@ -46,7 +46,7 @@ static u8 *mkfeatures(const tal_t *ctx, const u32 *arr, size_t n)
 	u8 *f = tal_arr(ctx, u8, 0);
 
 	for (size_t i = 0; i < n; i++)
-		set_bit(&f, arr[i]);
+		set_feature_bit(&f, arr[i]);
 	return f;
 }
 
@@ -62,7 +62,7 @@ u8 *get_offered_localfeatures(const tal_t *ctx)
 			  our_localfeatures, ARRAY_SIZE(our_localfeatures));
 }
 
-static bool feature_set(const u8 *features, size_t bit)
+bool feature_is_set(const u8 *features, size_t bit)
 {
 	size_t bytenum = bit / 8;
 
@@ -74,8 +74,8 @@ static bool feature_set(const u8 *features, size_t bit)
 
 bool feature_offered(const u8 *features, size_t f)
 {
-	return feature_set(features, COMPULSORY_FEATURE(f))
-		|| feature_set(features, OPTIONAL_FEATURE(f));
+	return feature_is_set(features, COMPULSORY_FEATURE(f))
+		|| feature_is_set(features, OPTIONAL_FEATURE(f));
 }
 
 static bool feature_supported(int feature_bit,
@@ -124,8 +124,8 @@ bool features_supported(const u8 *globalfeatures, const u8 *localfeatures)
 {
 	/* BIT 2 would logically be "compulsory initial_routing_sync", but
 	 * that does not exist, so we special case it. */
-	if (feature_set(localfeatures,
-			COMPULSORY_FEATURE(LOCAL_INITIAL_ROUTING_SYNC)))
+	if (feature_is_set(localfeatures,
+			   COMPULSORY_FEATURE(LOCAL_INITIAL_ROUTING_SYNC)))
 		return false;
 
 	return all_supported_features(globalfeatures,

common/features.h

@@ -21,6 +21,10 @@ bool global_feature_negotiated(const u8 *gfeatures, size_t f);
 /* Return a list of what features we advertize. */
 const char **list_supported_features(const tal_t *ctx);
 
+/* Low-level helpers to deal with big-endian bitfields. */
+bool feature_is_set(const u8 *features, size_t bit);
+void set_feature_bit(u8 **ptr, u32 bit);
+
 /* BOLT #9:
  *
  * Flags are numbered from the least-significant bit, at bit 0 (i.e. 0x1,

common/test/run-features.c

@@ -23,12 +23,12 @@ int main(void)
 
 	bits = tal_arr(tmpctx, u8, 0);
 	for (size_t i = 0; i < 100; i += 3)
-		set_bit(&bits, i);
+		set_feature_bit(&bits, i);
 	for (size_t i = 0; i < 100; i++)
 		assert(test_bit(bits, i / 8, i % 8) == ((i % 3) == 0));
 
 	for (size_t i = 0; i < 100; i++)
-		assert(feature_set(bits, i) == ((i % 3) == 0));
+		assert(feature_is_set(bits, i) == ((i % 3) == 0));
 
 	/* Simple test: single byte */
 	bits = tal_arr(tmpctx, u8, 1);
@@ -75,18 +75,18 @@ int main(void)
 	/* We can add random odd features, no problem. */
 	for (size_t i = 1; i < 16; i += 2) {
 		bits = tal_dup_arr(tmpctx, u8, lf, tal_count(lf), 0);
-		set_bit(&bits, i);
+		set_feature_bit(&bits, i);
 		assert(features_supported(gf, bits));
 
 		bits = tal_dup_arr(tmpctx, u8, gf, tal_count(gf), 0);
-		set_bit(&bits, i);
+		set_feature_bit(&bits, i);
 		assert(features_supported(bits, lf));
 	}
 
 	/* We can't add random even features. */
 	for (size_t i = 0; i < 16; i += 2) {
 		bits = tal_dup_arr(tmpctx, u8, lf, tal_count(lf), 0);
-		set_bit(&bits, i);
+		set_feature_bit(&bits, i);
 
 		/* Special case for missing compulsory feature */
 		if (i == 2) {
@@ -98,7 +98,7 @@ int main(void)
 		}
 
 		bits = tal_dup_arr(tmpctx, u8, gf, tal_count(gf), 0);
-		set_bit(&bits, i);
+		set_feature_bit(&bits, i);
 		assert(features_supported(bits, lf)
 		       == feature_supported(i, our_globalfeatures,
 					    ARRAY_SIZE(our_globalfeatures)));