diff --git a/Makefile b/Makefile
index b39bd27..6f388f2 100644
--- a/Makefile
+++ b/Makefile
@@ -5,10 +5,10 @@ CXXFLAGS=	$(CFLAGS)
 AR=			ar
 DFLAGS=		-DHAVE_PTHREAD #-D_NO_SSE2 #-D_FILE_OFFSET_BITS=64
 LOBJS=		bwa.o bamlite.o utils.o bwt.o bwtio.o bwtaln.o bwtgap.o bntseq.o stdaln.o \
-			bwaseqio.o
+			bwaseqio.o bwase.o kstring.o
 AOBJS=		QSufSort.o bwt_gen.o \
 			is.o bwtmisc.o bwtindex.o ksw.o simple_dp.o \
-			bwase.o bwape.o kstring.o cs2nt.o \
+			bwape.o cs2nt.o \
 			bwtsw2_core.o bwtsw2_main.o bwtsw2_aux.o bwt_lite.o \
 			bwtsw2_chain.o fastmap.o bwtsw2_pair.o
 PROG=		bwa
diff --git a/bwa.c b/bwa.c
index 3c6fbfd..6f3dbd4 100644
--- a/bwa.c
+++ b/bwa.c
@@ -11,6 +11,7 @@
 #endif
 
 extern unsigned char nst_nt4_table[256];
+extern void seq_reverse(int len, uint8_t *seq, int is_comp);
 
 bwa_opt_t bwa_def_opt = { 11, 4, -1, 1, 6, 32, 2, 0.04 };
 
@@ -92,7 +93,6 @@ void bwa_aux_destroy(bwa_aux_t *p)
 bwa_alnpre_t *bwa_aln_pre(const bwa_idx_t *idx, bwa_aux_t *aux, const char *seq, int *n_aln)
 {
 	extern int bwt_cal_width(const bwt_t *bwt, int len, const ubyte_t *str, bwt_width_t *width);
-	extern void seq_reverse(int len, uint8_t *seq, int is_comp);
 	int i, seq_len, buf_len;
 	bwt_width_t *w, *seed_w;
 	uint8_t *s;
@@ -124,25 +124,76 @@ bwa_alnpre_t *bwa_aln_pre(const bwa_idx_t *idx, bwa_aux_t *aux, const char *seq,
 		s[i] = s[i] > 3? 4 : 3 - s[i];
 	return (bwa_alnpre_t*)bwt_match_gap(idx->bwt, seq_len, s, w, seq_len <= aux->opt->seed_len? 0 : seed_w, &opt2, n_aln, aux->stack);
 }
-/*
+
+static void compute_NM(const uint8_t *pac, uint64_t l_pac, uint8_t *seq, int64_t pos, int n_cigar, uint32_t *cigar, int *n_mm, int *n_gaps)
+{
+	uint64_t x = pos, z;
+	int k, y = 0;
+	*n_mm = *n_gaps = 0;
+	for (k = 0; k < n_cigar; ++k) {
+		int l = cigar[k]>>4;
+		int op = cigar[k]&0xf;
+		if (op == 0) { // match/mismatch
+			for (z = 0; z < l && x + z < l_pac; ++z) {
+				int c = pac[(x+z)>>2] >> ((~(x+z)&3)<<1) & 3;
+				if (c > 3 || seq[y+z] > 3 || c != seq[y+z]) ++(*n_mm);
+			}
+		}
+		if (op == 1 || op == 2) (*n_gaps) += l;
+		if (op == 0 || op == 2) x += l;
+		if (op == 0 || op == 1 || op == 4) y += l;
+	}
+}
+
 bwa_aln_t bwa_sa2aln(const bwa_idx_t *idx, bwa_aux_t *aux, const char *seq, uint64_t sa, int n_gaps)
 {
 	extern bwtint_t bwa_sa2pos(const bntseq_t *bns, const bwt_t *bwt, bwtint_t sapos, int len, int *strand);
 	extern bwa_cigar_t *bwa_refine_gapped_core(bwtint_t l_pac, const ubyte_t *pacseq, int len, const uint8_t *seq, bwtint_t *_pos, int ext, int *n_cigar, int is_end_correct);
-	int strand, seq_len, n_cigar;
-	uint64_t pos;
+	int strand, seq_len, i, n_gap, n_mm;
+	uint64_t pos3;
 	uint8_t *s[2];
 	bwa_aln_t aln;
-	bwa_cigar_t *cigar16;
 
+	memset(&aln, 0, sizeof(bwa_aln_t));
 	seq_len = strlen(seq);
 	if (seq_len<<1 > aux->max_buf) {
 		aux->max_buf = seq_len<<1;
 		kroundup32(aux->max_buf);
 		aux->buf = realloc(aux->buf, aux->max_buf);
 	}
-	pos = bwa_sa2pos(idx->bns, idx->bwt, sa, seq_len, &strand);
-	cigar16 = bwa_refine_gapped_core(idx->bns->l_pac, idx->pac, len, s[strand], &pos, strand? n_gaps : -n_gaps, &n_cigar, 1);
+	s[0] = aux->buf;
+	s[1] = s[0] + seq_len;
+	for (i = 0; i < seq_len; ++i)
+		s[0][i] = s[1][i] = nst_nt4_table[(int)seq[i]];
+	seq_reverse(seq_len, s[1], 1);
+	aln.pac_pos = bwa_sa2pos(idx->bns, idx->bwt, sa, seq_len, &strand);
+	if (strand) aln.flag |= 16;
+	if (n_gaps) { // only for gapped alignment
+		int n_cigar;
+		bwa_cigar_t *cigar16;
+		cigar16 = bwa_refine_gapped_core(idx->bns->l_pac, idx->pac, seq_len, s[strand], &aln.pac_pos, strand? n_gaps : -n_gaps, &n_cigar, 1);
+		aln.n_cigar = n_cigar;
+		aln.cigar = malloc(n_cigar * 4);
+		for (i = 0, pos3 = aln.pac_pos; i < n_cigar; ++i) {
+			int op = cigar16[i]>>14;
+			int len = cigar16[i]&0x3fff;
+			if (op == 3) op = 4; // the 16-bit CIGAR is different from the 32-bit CIGAR
+			aln.cigar[i] = len<<4 | op;
+			if (op == 0 || op == 2) pos3 += len;
+		}
+		free(cigar16);
+	} else { // ungapped
+		aln.n_cigar = 1;
+		aln.cigar = malloc(4);
+		aln.cigar[0] = seq_len<<4 | 0;
+		pos3 = aln.pac_pos + seq_len;
+	}
+	aln.n_n = bns_cnt_ambi(idx->bns, aln.pac_pos, pos3 - aln.pac_pos, &aln.ref_id);
+	aln.offset = aln.pac_pos - idx->bns->anns[aln.ref_id].offset;
+	if (pos3 - idx->bns->anns[aln.ref_id].offset > idx->bns->anns[aln.ref_id].len) // read mapped beyond the end of a sequence
+		aln.flag |= 4; // read unmapped
+	compute_NM(idx->pac, idx->bns->l_pac, s[strand], aln.pac_pos, aln.n_cigar, aln.cigar, &n_mm, &n_gap);
+	aln.n_mm = n_mm;
+	aln.n_gap = n_gap;
 	return aln;
 }
-*/
diff --git a/bwa.h b/bwa.h
index 01eddcf..303c983 100644
--- a/bwa.h
+++ b/bwa.h
@@ -26,9 +26,11 @@ typedef struct {
 } bwa_alnpre_t;
 
 typedef struct {
-	uint32_t n_cigar:15, gap:8, mm:8, strand:1;
-	uint32_t ref_id;
-	uint64_t offset;
+	uint32_t n_n:8, n_gap:12, n_mm:12;
+	int32_t ref_id;
+	uint32_t offset;
+	uint32_t n_cigar:16, flag:16;
+	uint64_t pac_pos;
 	uint32_t *cigar;
 } bwa_aln_t;
 
@@ -43,6 +45,7 @@ extern "C" {
 	bwa_aux_t *bwa_aux_init(const bwa_opt_t *opt, int max_score);
 	void bwa_aux_destroy(bwa_aux_t *p);
 	bwa_alnpre_t *bwa_aln_pre(const bwa_idx_t *idx, bwa_aux_t *aux, const char *seq, int *n_aln);
+	bwa_aln_t bwa_sa2aln(const bwa_idx_t *idx, bwa_aux_t *aux, const char *seq, uint64_t sa, int n_gaps);
 
 #ifdef __cplusplus
 }
diff --git a/bwase.c b/bwase.c
index c88cae5..35744e7 100644
--- a/bwase.c
+++ b/bwase.c
@@ -328,7 +328,7 @@ void bwa_refine_gapped(const bntseq_t *bns, int n_seqs, bwa_seq_t *seqs, ubyte_t
 		s->cigar = bwa_refine_gapped_core(bns->l_pac, pacseq, s->len, s->strand? s->rseq : s->seq, &s->pos,
 									  (s->strand? 1 : -1) * (s->n_gapo + s->n_gape), &s->n_cigar, 1);
 	}
-
+#if 0
 	if (ntbns) { // in color space
 		for (i = 0; i < n_seqs; ++i) {
 			bwa_seq_t *s = seqs + i;
@@ -349,7 +349,7 @@ void bwa_refine_gapped(const bntseq_t *bns, int n_seqs, bwa_seq_t *seqs, ubyte_t
 			}
 		}
 	}
-
+#endif
 	// generate MD tag
 	str = (kstring_t*)calloc(1, sizeof(kstring_t));
 	for (i = 0; i != n_seqs; ++i) {
@@ -602,7 +602,7 @@ void bwa_sai2sam_se_core(const char *prefix, const char *fn_sa, const char *fn_f
 	if (!(opt.mode & BWA_MODE_COMPREAD)) // in color space; initialize ntpac
 		ntbns = bwa_open_nt(prefix);
 	bwa_print_sam_SQ(bns);
-	bwa_print_sam_PG();
+	//bwa_print_sam_PG();
 	// set ks
 	ks = bwa_open_reads(opt.mode, fn_fa);
 	// core loop