finished aztec code generator.

fixes #10

utils/bitlist.go

@@ -76,7 +76,7 @@ func (bl *BitList) AddByte(b byte) {
 
 // AddBits appends the last (LSB) 'count' bits of 'b' the the end of the list
 func (bl *BitList) AddBits(b int, count byte) {
-	for i := int(count - 1); i >= 0; i-- {
+	for i := int(count) - 1; i >= 0; i-- {
 		bl.AddBit(((b >> uint(i)) & 1) == 1)
 	}
 }

utils/galoisfield.go

@@ -2,28 +2,31 @@ package utils
 
 // GaloisField encapsulates galois field arithmetics
 type GaloisField struct {
+	Size    int
+	Base    int
 	ALogTbl []int
 	LogTbl  []int
 }
 
-// NewGaloisField creates a new falois field
-func NewGaloisField(pp int) *GaloisField {
+// NewGaloisField creates a new galois field
+func NewGaloisField(pp, fieldSize, b int) *GaloisField {
 	result := new(GaloisField)
-	fldSize := 256
 
-	result.ALogTbl = make([]int, fldSize)
-	result.LogTbl = make([]int, fldSize)
+	result.Size = fieldSize
+	result.Base = b
+	result.ALogTbl = make([]int, fieldSize)
+	result.LogTbl = make([]int, fieldSize)
 
 	x := 1
-	for i := 0; i < fldSize; i++ {
+	for i := 0; i < fieldSize; i++ {
 		result.ALogTbl[i] = x
 		x = x * 2
-		if x >= fldSize {
-			x = (x ^ pp) & (fldSize - 1)
+		if x >= fieldSize {
+			x = (x ^ pp) & (fieldSize - 1)
 		}
 	}
 
-	for i := 0; i < fldSize; i++ {
+	for i := 0; i < fieldSize; i++ {
 		result.LogTbl[result.ALogTbl[i]] = int(i)
 	}
 
@@ -31,7 +34,7 @@ func NewGaloisField(pp int) *GaloisField {
 }
 
 func (gf *GaloisField) Zero() *GFPoly {
-	return NewGFPoly(gf, []byte{0})
+	return NewGFPoly(gf, []int{0})
 }
 
 // AddOrSub add or substract two numbers
@@ -44,7 +47,7 @@ func (gf *GaloisField) Multiply(a, b int) int {
 	if a == 0 || b == 0 {
 		return 0
 	}
-	return gf.ALogTbl[(gf.LogTbl[a]+gf.LogTbl[b])%255]
+	return gf.ALogTbl[(gf.LogTbl[a]+gf.LogTbl[b])%(gf.Size-1)]
 }
 
 // Divide divides two numbers
@@ -54,9 +57,9 @@ func (gf *GaloisField) Divide(a, b int) int {
 	} else if a == 0 {
 		return 0
 	}
-	return gf.ALogTbl[(gf.LogTbl[a]-gf.LogTbl[b])%255]
+	return gf.ALogTbl[(gf.LogTbl[a]-gf.LogTbl[b])%(gf.Size-1)]
 }
 
 func (gf *GaloisField) Invers(num int) int {
-	return gf.ALogTbl[255-gf.LogTbl[num]]
+	return gf.ALogTbl[(gf.Size-1)-gf.LogTbl[num]]
 }

utils/galoisfield_test.go

@@ -43,7 +43,7 @@ func Test_GF(t *testing.T) {
 		3, 6, 12, 24, 48, 96, 192, 173, 119, 238, 241, 207, 179, 75, 150, 1,
 	}
 
-	gf := NewGaloisField(301)
+	gf := NewGaloisField(301, 256, 1)
 	if len(gf.LogTbl) != len(gf.ALogTbl) || len(gf.LogTbl) != len(log) {
 		t.Fail()
 	}

utils/gfpoly.go

@@ -2,7 +2,7 @@ package utils
 
 type GFPoly struct {
 	gf           *GaloisField
-	Coefficients []byte
+	Coefficients []int
 }
 
 func (gp *GFPoly) Degree() int {
@@ -14,7 +14,7 @@ func (gp *GFPoly) Zero() bool {
 }
 
 // GetCoefficient returns the coefficient of x ^ degree
-func (gp *GFPoly) GetCoefficient(degree int) byte {
+func (gp *GFPoly) GetCoefficient(degree int) int {
 	return gp.Coefficients[gp.Degree()-degree]
 }
 
@@ -29,23 +29,23 @@ func (gp *GFPoly) AddOrSubstract(other *GFPoly) *GFPoly {
 	if len(smallCoeff) > len(largeCoeff) {
 		largeCoeff, smallCoeff = smallCoeff, largeCoeff
 	}
-	sumDiff := make([]byte, len(largeCoeff))
+	sumDiff := make([]int, len(largeCoeff))
 	lenDiff := len(largeCoeff) - len(smallCoeff)
 	copy(sumDiff, largeCoeff[:lenDiff])
 	for i := lenDiff; i < len(largeCoeff); i++ {
-		sumDiff[i] = byte(gp.gf.AddOrSub(int(smallCoeff[i-lenDiff]), int(largeCoeff[i])))
+		sumDiff[i] = int(gp.gf.AddOrSub(int(smallCoeff[i-lenDiff]), int(largeCoeff[i])))
 	}
 	return NewGFPoly(gp.gf, sumDiff)
 }
 
-func (gp *GFPoly) MultByMonominal(degree int, coeff byte) *GFPoly {
+func (gp *GFPoly) MultByMonominal(degree int, coeff int) *GFPoly {
 	if coeff == 0 {
 		return gp.gf.Zero()
 	}
 	size := len(gp.Coefficients)
-	result := make([]byte, size+degree)
+	result := make([]int, size+degree)
 	for i := 0; i < size; i++ {
-		result[i] = byte(gp.gf.Multiply(int(gp.Coefficients[i]), int(coeff)))
+		result[i] = int(gp.gf.Multiply(int(gp.Coefficients[i]), int(coeff)))
 	}
 	return NewGFPoly(gp.gf, result)
 }
@@ -58,12 +58,12 @@ func (gp *GFPoly) Multiply(other *GFPoly) *GFPoly {
 	aLen := len(aCoeff)
 	bCoeff := other.Coefficients
 	bLen := len(bCoeff)
-	product := make([]byte, aLen+bLen-1)
+	product := make([]int, aLen+bLen-1)
 	for i := 0; i < aLen; i++ {
 		ac := int(aCoeff[i])
 		for j := 0; j < bLen; j++ {
 			bc := int(bCoeff[j])
-			product[i+j] = byte(gp.gf.AddOrSub(int(product[i+j]), gp.gf.Multiply(ac, bc)))
+			product[i+j] = int(gp.gf.AddOrSub(int(product[i+j]), gp.gf.Multiply(ac, bc)))
 		}
 	}
 	return NewGFPoly(gp.gf, product)
@@ -77,7 +77,7 @@ func (gp *GFPoly) Divide(other *GFPoly) (quotient *GFPoly, remainder *GFPoly) {
 	inversDenomLeadTerm := fld.Invers(int(denomLeadTerm))
 	for remainder.Degree() >= other.Degree() && !remainder.Zero() {
 		degreeDiff := remainder.Degree() - other.Degree()
-		scale := byte(fld.Multiply(int(remainder.GetCoefficient(remainder.Degree())), inversDenomLeadTerm))
+		scale := int(fld.Multiply(int(remainder.GetCoefficient(remainder.Degree())), inversDenomLeadTerm))
 		term := other.MultByMonominal(degreeDiff, scale)
 		itQuot := NewMonominalPoly(fld, degreeDiff, scale)
 		quotient = quotient.AddOrSubstract(itQuot)
@@ -86,16 +86,16 @@ func (gp *GFPoly) Divide(other *GFPoly) (quotient *GFPoly, remainder *GFPoly) {
 	return
 }
 
-func NewMonominalPoly(field *GaloisField, degree int, coeff byte) *GFPoly {
+func NewMonominalPoly(field *GaloisField, degree int, coeff int) *GFPoly {
 	if coeff == 0 {
 		return field.Zero()
 	}
-	result := make([]byte, degree+1)
+	result := make([]int, degree+1)
 	result[0] = coeff
 	return NewGFPoly(field, result)
 }
 
-func NewGFPoly(field *GaloisField, coefficients []byte) *GFPoly {
+func NewGFPoly(field *GaloisField, coefficients []int) *GFPoly {
 	for len(coefficients) > 1 && coefficients[0] == 0 {
 		coefficients = coefficients[1:]
 	}

utils/reedsolomon.go

@@ -0,0 +1,44 @@
+package utils
+
+import (
+	"sync"
+)
+
+type ReedSolomonEncoder struct {
+	gf        *GaloisField
+	polynomes []*GFPoly
+	m         *sync.Mutex
+}
+
+func NewReedSolomonEncoder(gf *GaloisField) *ReedSolomonEncoder {
+	return &ReedSolomonEncoder{
+		gf, []*GFPoly{NewGFPoly(gf, []int{1})}, new(sync.Mutex),
+	}
+}
+
+func (rs *ReedSolomonEncoder) getPolynomial(degree int) *GFPoly {
+	rs.m.Lock()
+	defer rs.m.Unlock()
+
+	if degree >= len(rs.polynomes) {
+		last := rs.polynomes[len(rs.polynomes)-1]
+		for d := len(rs.polynomes); d <= degree; d++ {
+			next := last.Multiply(NewGFPoly(rs.gf, []int{1, rs.gf.ALogTbl[d-1+rs.gf.Base]}))
+			rs.polynomes = append(rs.polynomes, next)
+			last = next
+		}
+	}
+	return rs.polynomes[degree]
+}
+
+func (rs *ReedSolomonEncoder) Encode(data []int, eccCount int) []int {
+	generator := rs.getPolynomial(eccCount)
+	info := NewGFPoly(rs.gf, data)
+	info = info.MultByMonominal(eccCount, 1)
+	_, remainder := info.Divide(generator)
+
+	result := make([]int, eccCount)
+	numZero := int(eccCount) - len(remainder.Coefficients)
+	copy(result[numZero:], remainder.Coefficients)
+	return result
+}