Make sure that we don't compute a block size larger than MAX_BLOCK_SIZE.

generator.c

@@ -146,9 +146,11 @@ static void sum_sizes_sqroot(struct sum_struct *sum, uint64 len)
 	else {
 		int32 c;
 		uint64 l;
-		for (c = 1, l = len; l >>= 2; c <<= 1) {
-		    assert(c > 0);
-		}
+		int cnt;
+		for (c = 1, l = len, cnt = 0; l >>= 2; c <<= 1, cnt++) {}
+		if (cnt >= 31 || c >= MAX_BLOCK_SIZE)
+			blength = MAX_BLOCK_SIZE;
+		else {
 		    blength = 0;
 		    do {
 			    blength |= c;
@@ -158,6 +160,7 @@ static void sum_sizes_sqroot(struct sum_struct *sum, uint64 len)
 		    } while (c >= 8);	/* round to multiple of 8 */
 		    blength = MAX(blength, BLOCK_SIZE);
 		}
+	}
 
 	if (protocol_version < 27) {
 		s2length = csum_length;