bitcoin/tx, protobuf_convert: support BIP68 as implemented.

The format for both the nSequence field and the stack arg for
OP_CHECKSEQUENCEVERIFY is either:

  Time-relative:	[Bit 22 = 1] 00000 <time-shifted-by-9>
  Block-relative:	[Bit 22 = 0] 00000 <number of blocks>

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

bitcoin/tx.c

@@ -550,13 +550,10 @@ bool bitcoin_tx_write(int fd, const struct bitcoin_tx *tx)
 u32 bitcoin_nsequence(u32 locktime)
 {
 #ifdef HAS_BIP68
-	/* BIP66 style sequence numbers */
-	if (locktime >= 500000000)
-		/* A relative time.  Set bit 30, shift by 5. */
-		return 0x40000000 | ((locktime - 500000000) << 5);
-	else
-		/* A block height.  Shift by 14. */
-		return locktime << 14;
+	/* FIXME: return fail to caller. */
+	/* Can't set disable bit, or other bits except low 16 and bit 22 */
+	assert(!(locktime & ~((1 << 22) | 0xFFFF)));
+	return locktime;
 #else
 	/* Alpha uses the original proposal: simply invert the bits. */
 	return ~locktime;

protobuf_convert.c

@@ -128,7 +128,28 @@ static bool proto_to_locktime(const Locktime *l, uint32_t off,
 
 bool proto_to_rel_locktime(const Locktime *l, uint32_t *locktime)
 {
+	/* Original proposal from Elements Alpha was simply locktime. */
+#ifdef HAS_BIP68
+	switch (l->locktime_case) {
+	case LOCKTIME__LOCKTIME_SECONDS:
+		*locktime = (1 << 22) | (l->seconds / 512);
+		if (l->seconds / 512 > 0xFFFF)
+			return false;
+		break;
+	case LOCKTIME__LOCKTIME_BLOCKS:
+		*locktime = l->blocks;
+		if (l->blocks > 0xFFFF)
+			return false;
+		break;
+	default:
+		return false;
+	}
+	/* No other bits should be set. */
+	assert((*locktime & ~((1 << 22) | 0xFFFF)) == 0);
+	return true;
+#else
 	return proto_to_locktime(l, 500000000, locktime);
+#endif
 }
 
 bool proto_to_abs_locktime(const Locktime *l, uint32_t *locktime)