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author | Wim <wim@42.be> | 2022-01-31 00:27:37 +0100 |
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committer | Wim <wim@42.be> | 2022-03-20 14:57:48 +0100 |
commit | e3cafeaf9292f67459ff1d186f68283bfaedf2ae (patch) | |
tree | b69c39620aa91dba695b3b935c6651c0fb37ce75 /vendor/rsc.io/qr/gf256 | |
parent | e7b193788a56ee7cdb02a87a9db0ad6724ef66d5 (diff) | |
download | matterbridge-msglm-e3cafeaf9292f67459ff1d186f68283bfaedf2ae.tar.gz matterbridge-msglm-e3cafeaf9292f67459ff1d186f68283bfaedf2ae.tar.bz2 matterbridge-msglm-e3cafeaf9292f67459ff1d186f68283bfaedf2ae.zip |
Add dependencies/vendor (whatsapp)
Diffstat (limited to 'vendor/rsc.io/qr/gf256')
-rw-r--r-- | vendor/rsc.io/qr/gf256/gf256.go | 241 |
1 files changed, 241 insertions, 0 deletions
diff --git a/vendor/rsc.io/qr/gf256/gf256.go b/vendor/rsc.io/qr/gf256/gf256.go new file mode 100644 index 00000000..05e56455 --- /dev/null +++ b/vendor/rsc.io/qr/gf256/gf256.go @@ -0,0 +1,241 @@ +// Copyright 2010 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Package gf256 implements arithmetic over the Galois Field GF(256). +package gf256 // import "rsc.io/qr/gf256" + +import "strconv" + +// A Field represents an instance of GF(256) defined by a specific polynomial. +type Field struct { + log [256]byte // log[0] is unused + exp [510]byte +} + +// NewField returns a new field corresponding to the polynomial poly +// and generator α. The Reed-Solomon encoding in QR codes uses +// polynomial 0x11d with generator 2. +// +// The choice of generator α only affects the Exp and Log operations. +func NewField(poly, α int) *Field { + if poly < 0x100 || poly >= 0x200 || reducible(poly) { + panic("gf256: invalid polynomial: " + strconv.Itoa(poly)) + } + + var f Field + x := 1 + for i := 0; i < 255; i++ { + if x == 1 && i != 0 { + panic("gf256: invalid generator " + strconv.Itoa(α) + + " for polynomial " + strconv.Itoa(poly)) + } + f.exp[i] = byte(x) + f.exp[i+255] = byte(x) + f.log[x] = byte(i) + x = mul(x, α, poly) + } + f.log[0] = 255 + for i := 0; i < 255; i++ { + if f.log[f.exp[i]] != byte(i) { + panic("bad log") + } + if f.log[f.exp[i+255]] != byte(i) { + panic("bad log") + } + } + for i := 1; i < 256; i++ { + if f.exp[f.log[i]] != byte(i) { + panic("bad log") + } + } + + return &f +} + +// nbit returns the number of significant in p. +func nbit(p int) uint { + n := uint(0) + for ; p > 0; p >>= 1 { + n++ + } + return n +} + +// polyDiv divides the polynomial p by q and returns the remainder. +func polyDiv(p, q int) int { + np := nbit(p) + nq := nbit(q) + for ; np >= nq; np-- { + if p&(1<<(np-1)) != 0 { + p ^= q << (np - nq) + } + } + return p +} + +// mul returns the product x*y mod poly, a GF(256) multiplication. +func mul(x, y, poly int) int { + z := 0 + for x > 0 { + if x&1 != 0 { + z ^= y + } + x >>= 1 + y <<= 1 + if y&0x100 != 0 { + y ^= poly + } + } + return z +} + +// reducible reports whether p is reducible. +func reducible(p int) bool { + // Multiplying n-bit * n-bit produces (2n-1)-bit, + // so if p is reducible, one of its factors must be + // of np/2+1 bits or fewer. + np := nbit(p) + for q := 2; q < 1<<(np/2+1); q++ { + if polyDiv(p, q) == 0 { + return true + } + } + return false +} + +// Add returns the sum of x and y in the field. +func (f *Field) Add(x, y byte) byte { + return x ^ y +} + +// Exp returns the base-α exponential of e in the field. +// If e < 0, Exp returns 0. +func (f *Field) Exp(e int) byte { + if e < 0 { + return 0 + } + return f.exp[e%255] +} + +// Log returns the base-α logarithm of x in the field. +// If x == 0, Log returns -1. +func (f *Field) Log(x byte) int { + if x == 0 { + return -1 + } + return int(f.log[x]) +} + +// Inv returns the multiplicative inverse of x in the field. +// If x == 0, Inv returns 0. +func (f *Field) Inv(x byte) byte { + if x == 0 { + return 0 + } + return f.exp[255-f.log[x]] +} + +// Mul returns the product of x and y in the field. +func (f *Field) Mul(x, y byte) byte { + if x == 0 || y == 0 { + return 0 + } + return f.exp[int(f.log[x])+int(f.log[y])] +} + +// An RSEncoder implements Reed-Solomon encoding +// over a given field using a given number of error correction bytes. +type RSEncoder struct { + f *Field + c int + gen []byte + lgen []byte + p []byte +} + +func (f *Field) gen(e int) (gen, lgen []byte) { + // p = 1 + p := make([]byte, e+1) + p[e] = 1 + + for i := 0; i < e; i++ { + // p *= (x + Exp(i)) + // p[j] = p[j]*Exp(i) + p[j+1]. + c := f.Exp(i) + for j := 0; j < e; j++ { + p[j] = f.Mul(p[j], c) ^ p[j+1] + } + p[e] = f.Mul(p[e], c) + } + + // lp = log p. + lp := make([]byte, e+1) + for i, c := range p { + if c == 0 { + lp[i] = 255 + } else { + lp[i] = byte(f.Log(c)) + } + } + + return p, lp +} + +// NewRSEncoder returns a new Reed-Solomon encoder +// over the given field and number of error correction bytes. +func NewRSEncoder(f *Field, c int) *RSEncoder { + gen, lgen := f.gen(c) + return &RSEncoder{f: f, c: c, gen: gen, lgen: lgen} +} + +// ECC writes to check the error correcting code bytes +// for data using the given Reed-Solomon parameters. +func (rs *RSEncoder) ECC(data []byte, check []byte) { + if len(check) < rs.c { + panic("gf256: invalid check byte length") + } + if rs.c == 0 { + return + } + + // The check bytes are the remainder after dividing + // data padded with c zeros by the generator polynomial. + + // p = data padded with c zeros. + var p []byte + n := len(data) + rs.c + if len(rs.p) >= n { + p = rs.p + } else { + p = make([]byte, n) + } + copy(p, data) + for i := len(data); i < len(p); i++ { + p[i] = 0 + } + + // Divide p by gen, leaving the remainder in p[len(data):]. + // p[0] is the most significant term in p, and + // gen[0] is the most significant term in the generator, + // which is always 1. + // To avoid repeated work, we store various values as + // lv, not v, where lv = log[v]. + f := rs.f + lgen := rs.lgen[1:] + for i := 0; i < len(data); i++ { + c := p[i] + if c == 0 { + continue + } + q := p[i+1:] + exp := f.exp[f.log[c]:] + for j, lg := range lgen { + if lg != 255 { // lgen uses 255 for log 0 + q[j] ^= exp[lg] + } + } + } + copy(check, p[len(data):]) + rs.p = p +} |