diff --git a/pkg/obialign/fastlcs.go b/pkg/obialign/fastlcs.go
new file mode 100644
index 0000000..86770ca
--- /dev/null
+++ b/pkg/obialign/fastlcs.go
@@ -0,0 +1,216 @@
+package obialign
+
+import (
+	"log"
+
+	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiseq"
+)
+
+// Out values are always the smallest
+// Among in values, they rank according to their score
+// For equal score the shortest path is the best
+func _encodeValues(score, length int, out bool) uint64 {
+	const mask = uint64(1<<16) - 1
+	us := uint64(score)
+	fo := (us << 16) | (uint64((^length)-1) & mask)
+	if !out {
+		fo |= (uint64(1) << 32)
+	}
+	return fo
+}
+
+func _decodeValues(value uint64) (int, int, bool) {
+	const mask = uint64(1<<16) - 1
+	score := int((value >> 16) & mask)
+	length := int(((value + 1) ^ mask) & mask)
+	out := (value & (1 << 32)) == 0
+	return score, length, out
+}
+
+func _incpath(value uint64) uint64 {
+	return value - 1
+}
+
+func _incscore(value uint64) uint64 {
+	const incr = uint64(1) << 16
+	return value + incr
+}
+
+func _setout(value uint64) uint64 {
+	const outmask = uint64(1) << 32
+	return value | outmask
+}
+
+func _isout(value uint64) bool {
+	const outmask = uint64(1) << 32
+	return (value & outmask) == 0
+}
+
+var _empty = _encodeValues(0, 0, false)
+var _out = _encodeValues(0, 3000, true)
+
+func FastLCSScore(seqA, seqB *obiseq.BioSequence, maxError int) (int, int) {
+
+	// x:=_encodeValues(12,0,false)
+	// xs,xl,xo := _decodeValues(x)
+	// log.Println(x,xs,xl,xo)
+	// x=_encodeValues(12,1,false)
+	// xs,xl,xo = _decodeValues(x)
+	// log.Println(x,xs,xl,xo)
+	// x=_encodeValues(12,2,false)
+	// xs,xl,xo = _decodeValues(x)
+	// log.Println(x,xs,xl,xo)
+
+	lA := seqA.Length()
+	lB := seqB.Length()
+
+	// Ensure that A is the longest
+	if lA < lB {
+		seqA, seqB = seqB, seqA
+		lA, lB = lB, lA
+	}
+
+	delta := lA - lB
+
+	// The difference of length is larger the maximum allowed errors
+	if delta > maxError {
+		//	log.Println("Too large difference of length")
+		return -1, -1
+	}
+
+	// Doit-on vraiment diviser par deux ??? pas certain
+	extra := ((maxError - delta) / 2) + 1
+
+	even := 1 + delta + 2*extra
+	width := 2*even - 1
+
+	previous := make([]uint64, width)
+	current := make([]uint64, width)
+
+	// Initialise the first line
+
+	for j := 0; j < width; j++ {
+		if (j == extra+even) || (j == extra+even-1) {
+			previous[j] = _encodeValues(0, 1, false)
+		} else {
+			previous[j] = _empty
+		}
+	}
+
+	N := lB + ((delta) >> 1)
+	X := width
+
+	// log.Println("N = ", N)
+
+	for y := 1; y <= N; y++ {
+		// in_matrix := false
+		for x := 0; x < width; x++ {
+			X = y * width + x
+			modulo := X % width
+			begin := X - modulo
+			quotien := begin / width
+
+			i := quotien + extra - modulo
+			j := quotien - extra + modulo
+
+			if x >= even {
+				i += even
+				j += 1 - even
+			}
+
+			//log.Println(X, i, j, i < 0 || j < 0 || i > lB || j > lA)
+
+			// We are out of tha alignement matrix
+			if i < 0 || j < 0 || i > lB || j > lA {
+				X++
+				continue
+			}
+
+			var Sdiag, Sleft, Sup uint64
+
+			switch {
+
+			case i == 0:
+				Sup = _encodeValues(0, 30000, false)
+				Sdiag = _encodeValues(0, 30000, false)
+				Sleft = _encodeValues(0, j-1, false)
+			case j == 0:
+				Sup = _encodeValues(0, i-1, false)
+				Sdiag = _encodeValues(0, 30000, false)
+				Sleft = _encodeValues(0, 30000, false)
+			default:
+				Sdiag = previous[x]
+				if x >= even {
+					Sleft = current[x-even]
+					Sup = current[x-even+1]
+				} else {
+					if x < (even - 1) {
+						Sup = previous[x+even]
+					} else {
+						Sup = _out
+					}
+					if x > 0 {
+						Sleft = previous[x+even-1]
+					} else {
+						Sleft = _out
+					}
+				}
+			}
+
+			// log.Println("scores @",i,j,": ",Sdiag,Sup,Sleft)
+			// ds,dl,ol := _decodeValues(Sdiag)
+			// log.Println(ds,dl,ol)
+			// ds,dl,ol = _decodeValues(Sup)
+			// log.Println(ds,dl,ol)
+			// ds,dl,ol = _decodeValues(Sleft)
+			// log.Println(ds,dl,ol)
+			var score uint64
+			switch {
+			case Sdiag >= Sup && Sdiag >= Sleft:
+				score = Sdiag
+				if seqA.Sequence()[j-1] == seqB.Sequence()[i-1] {
+					score = _incscore(score)
+				}
+			case Sup >= Sleft:
+				score = Sup
+			default:
+				score = Sleft
+			}
+
+			if _isout(Sdiag) || _isout(Sup) || _isout(Sleft) {
+				score = _setout(score)
+			}
+
+			// if i < 5 && j < 5 {
+			// 	ds, dl, ol := _decodeValues(_incpath(score))
+			// 	log.Println("@", i, j,":", ds, dl, ol)
+			// }
+
+			current[x] = _incpath(score)
+
+			// if i == lB && j == lA {
+			// 	s, l, o := _decodeValues(current[x])
+			// 	log.Println("Results in ", x, y, "(", i, j, ") values : ", s, l, o)
+			// }
+
+			X++
+		}
+		// if !in_matrix {
+		// 	log.Fatalln("Never entred in the matrix", y, "/", N)
+		// }
+		previous, current = current, previous
+
+	}
+
+	s, l, o := _decodeValues(previous[(delta%2)*even+extra+(delta>>1)])
+
+	if o {
+		log.Println("Too much error", s, l, (lA%2)*even+(lA-lB), lA, lB, width, even, N)
+		return -1, -1
+	}
+
+	return s, l
+}
+
+// width * j + modulo + width * extra - width * modulo= X
+// i = (X - modulo)/width  - modulo + extra