Add dep

vendor/github.com/skip2/go-qrcode/reedsolomon/reed_solomon.go

@@ -0,0 +1,73 @@
+// go-qrcode
+// Copyright 2014 Tom Harwood
+
+// Package reedsolomon provides error correction encoding for QR Code 2005.
+//
+// QR Code 2005 uses a Reed-Solomon error correcting code to detect and correct
+// errors encountered during decoding.
+//
+// The generated RS codes are systematic, and consist of the input data with
+// error correction bytes appended.
+package reedsolomon
+
+import (
+	"log"
+
+	bitset "github.com/skip2/go-qrcode/bitset"
+)
+
+// Encode data for QR Code 2005 using the appropriate Reed-Solomon code.
+//
+// numECBytes is the number of error correction bytes to append, and is
+// determined by the target QR Code's version and error correction level.
+//
+// ISO/IEC 18004 table 9 specifies the numECBytes required. e.g. a 1-L code has
+// numECBytes=7.
+func Encode(data *bitset.Bitset, numECBytes int) *bitset.Bitset {
+	// Create a polynomial representing |data|.
+	//
+	// The bytes are interpreted as the sequence of coefficients of a polynomial.
+	// The last byte's value becomes the x^0 coefficient, the second to last
+	// becomes the x^1 coefficient and so on.
+	ecpoly := newGFPolyFromData(data)
+	ecpoly = gfPolyMultiply(ecpoly, newGFPolyMonomial(gfOne, numECBytes))
+
+	// Pick the generator polynomial.
+	generator := rsGeneratorPoly(numECBytes)
+
+	// Generate the error correction bytes.
+	remainder := gfPolyRemainder(ecpoly, generator)
+
+	// Combine the data & error correcting bytes.
+	// The mathematically correct answer is:
+	//
+	//	result := gfPolyAdd(ecpoly, remainder).
+	//
+	// The encoding used by QR Code 2005 is slightly different this result: To
+	// preserve the original |data| bit sequence exactly, the data and remainder
+	// are combined manually below. This ensures any most significant zero bits
+	// are preserved (and not optimised away).
+	result := bitset.Clone(data)
+	result.AppendBytes(remainder.data(numECBytes))
+
+	return result
+}
+
+// rsGeneratorPoly returns the Reed-Solomon generator polynomial with |degree|.
+//
+// The generator polynomial is calculated as:
+// (x + a^0)(x + a^1)...(x + a^degree-1)
+func rsGeneratorPoly(degree int) gfPoly {
+	if degree < 2 {
+		log.Panic("degree < 2")
+	}
+
+	generator := gfPoly{term: []gfElement{1}}
+
+	for i := 0; i < degree; i++ {
+		nextPoly := gfPoly{term: []gfElement{gfExpTable[i], 1}}
+		generator = gfPolyMultiply(generator, nextPoly)
+	}
+
+	return generator
+}