diff --git a/bntseq.c b/bntseq.c
index 15b369f..56df921 100644
--- a/bntseq.c
+++ b/bntseq.c
@@ -190,14 +190,14 @@ static void add1(const kseq_t *seq, bntseq_t *bns, FILE *fp, uint8_t *buf, int *
 				*q = bns->ambs + bns->n_holes;
 				(*q)->len = 1;
 				(*q)->offset = p->offset + i;
-				(*q)->amb = seq->seq.s[i];
+				(*q)->amb = 'N';
 				++p->n_ambs;
 				++bns->n_holes;
 			}
 		}
 		lasts = seq->seq.s[i];
 		{ // fill buffer
-			if (c >= 4) c = lrand48()&0x3;
+			if (c >= 4) c = c>>4;
 			if (*l_buf == 0x40000) {
 				fwrite(buf, 1, 0x10000, fp);
 				memset(buf, 0, 0x10000);
@@ -238,11 +238,16 @@ int64_t bns_fasta2bntseq(gzFile fp_fa, const char *prefix, int for_only)
 	memset(buf, 0, 0x10000);
 	// read sequences
 	while (kseq_read(seq) >= 0) {
-		for (i = 0; i < seq->seq.l; ++i) // convert to 2-bit encoding
+		for (i = 0; i < seq->seq.l; ++i) { // convert to 2-bit encoding
 			seq->seq.s[i] = nst_nt4_table[(int)seq->seq.s[i]];
+			if (seq->seq.s[i] > 3)
+				seq->seq.s[i] |= (lrand48()&3) << 4;
+		}
 		add1(seq, bns, fp, buf, &l_buf, &m_seqs, &m_holes, &q);
 		if (!for_only) {
-			seq_reverse(seq->seq.l, (uint8_t*)seq->seq.s, 1);
+			seq_reverse(seq->seq.l, (uint8_t*)seq->seq.s, 0); // reversed but not complemented
+			for (i = 0; i < seq->seq.l; ++i) // complement
+				seq->seq.s[i] = seq->seq.s[i] < 4? 3 - seq->seq.s[i] : ((3 - (seq->seq.s[i]>>4)) << 4 | 4);
 			add1(seq, bns, fp, buf, &l_buf, &m_seqs, &m_holes, &q);
 		}
 	}
diff --git a/bwt.c b/bwt.c
index e7da788..6f5eb67 100644
--- a/bwt.c
+++ b/bwt.c
@@ -282,9 +282,9 @@ int bwt_smem1(const bwt_t *bwt, int len, const uint8_t *q, int x, bwtintv_v *mem
 	prev = tmpvec[0]? tmpvec[0] : &a[0];
 	curr = tmpvec[1]? tmpvec[1] : &a[1];
 	bwt_set_intv(bwt, q[x], ik);
-
 	ik.info = x + 1;
-	for (i = x + 1; i < len; ++i) { // forward search
+
+	for (i = x + 1, curr->n = 0; i < len; ++i) { // forward search
 		if (q[i] > 3) break;
 		c = 3 - q[i];
 		bwt_extend(bwt, &ik, ok, 0);
@@ -298,6 +298,7 @@ int bwt_smem1(const bwt_t *bwt, int len, const uint8_t *q, int x, bwtintv_v *mem
 	ret = curr->a[0].info; // this will be the returned value
 	swap = curr; curr = prev; prev = swap;
 
+	if (x == 40) printf("[%lld,%lld,%lld]\n", prev->a[0].x[0], prev->a[0].x[1], prev->a[0].x[2]);
 	for (i = x - 1; i >= -1; --i) { // backward search for MEMs
 		if (q[i] > 3) break;
 		c = i < 0? 0 : q[i];
diff --git a/fastmap.c b/fastmap.c
index ee8e9b4..cf952b7 100644
--- a/fastmap.c
+++ b/fastmap.c
@@ -39,6 +39,27 @@ int main_fastmap(int argc, char *argv[])
 	while (kseq_read(seq) >= 0) {
 		for (i = 0; i < seq->seq.l; ++i)
 			seq->seq.s[i] = nst_nt4_table[(int)seq->seq.s[i]];
+		{
+			int beg = 98;
+			bwtintv_t ik, ok[4];
+			bwt_set_intv(bwt, seq->seq.s[seq->seq.l - 1], ik);
+			for (i = seq->seq.l - 2; i >= beg; --i) {
+				//printf("[%lld,%lld,%lld] @ %d\n", ik.x[0], ik.x[1], ik.x[2], i+1);
+				bwt_extend(bwt, &ik, ok, 1);
+				ik = ok[seq->seq.s[i]];
+				if (ik.x[2] == 0) break;
+			}
+			printf("[%lld,%lld,%lld] @ %d\n", ik.x[0], ik.x[1], ik.x[2], i+1);
+			printf("======================== %lld, [%lld,%lld,%lld,%lld]\n", bwt->primary, bwt->L2[1], bwt->L2[2]-bwt->L2[1], bwt->L2[3]-bwt->L2[2], bwt->L2[4]-bwt->L2[3]);
+			bwt_set_intv(bwt, seq->seq.s[beg], ik);
+			for (i = beg + 1; i < seq->seq.l; ++i) {
+				//printf("[%lld,%lld,%lld] @ %d\n", ik.x[0], ik.x[1], ik.x[2], i-1);
+				bwt_extend(bwt, &ik, ok, 0);
+				ik = ok[3-seq->seq.s[i]];
+				if (ik.x[2] == 0) break;
+			}
+			printf("[%lld,%lld,%lld] @ %d\n", ik.x[0], ik.x[1], ik.x[2], i-1);
+		}
 		bwt_smem(bwt, seq->seq.l, (uint8_t*)seq->seq.s, &mem, tvec);
 		printf(">%s\t%ld\n", seq->name.s, mem.n);
 		for (i = 0; i < mem.n; ++i) {