68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
-
|
return err
}
// ... and stage the rest of the data in the buffer
ctx.input = append(ctx.input, data[blockSize-bufferLength:]...)
return nil
}
// TODO allocate this on ctx.buffer ...
var buf []byte = make([]byte, 1, blockSize+1)
for block := 0; block < len(data)/blockSize; block++ {
for i := 0; i < blockSize; i++ {
var current byte = data[(block*blockSize)+i]
if ctx.table[ctx.hash] == current {
// Guess was right - don't output
buf[0] |= 1 << uint(i)
|
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
|
-
+
-
+
-
+
-
-
+
+
-
+
-
-
-
-
-
-
-
+
+
+
-
+
-
+
-
+
-
+
+
+
-
-
+
+
-
+
|
// Required to implement io.Reader
func (r decompressor) Read(output []byte) (int, error) {
return r(output)
}
// Returns an io.Reader implementation that wraps the provided io.Reader
// and decompresses data according to the predictor algorithm
func Decompressor(wrapped io.Reader) io.Reader {
func Decompressor(reader io.Reader) io.Reader {
var ctx context
ctx.input = make([]byte, 0, 8)
return decompressor(func(output []byte) (int, error) {
var (
err error
flags byte
readCount int
rc, total int
)
// Sanity check for space to read into
if len(output) == 0 {
return 0, nil
}
// Check whether we have leftover data in the buffer
if len(ctx.input) > 0 {
readCount = copy(output, ctx.input)
rc = copy(output, ctx.input)
// Check whether we still have leftover data in the buffer :)
if readCount < len(ctx.input) {
ctx.input = ctx.input[:copy(ctx.input, ctx.input[readCount:])]
if rc < len(ctx.input) {
ctx.input = ctx.input[:copy(ctx.input, ctx.input[rc:])]
}
return readCount, nil
return rc, nil
}
// This is single-iteration only but it is fine according to io.Reader's contract ?!
// TODO - read all bytes from a block based on the hamming weight of the flag
// and just shuffle them for predictions instead of bite-sized reads ;)
// Read the flags
readCount, err = wrapped.Read(ctx.input[:1])
if readCount == 0 || err != nil {
return readCount, err
rc, err = reader.Read(ctx.input[:1])
if rc == 0 || (err != nil && err != io.EOF) {
return rc, err
}
ctx.input = ctx.input[:8]
flags = ctx.input[0]
var i uint = 0
for ; i < 8; i++ {
if flags&(1<<i) > 0 {
// Guess was right
ctx.input[i] = ctx.table[ctx.hash]
} else {
readCount, err = wrapped.Read(ctx.input[i:(i + 1)])
rc, err = reader.Read(ctx.input[i:(i + 1)])
if err == io.EOF {
break
}
if err != nil {
return readCount, err
return rc, err
}
if readCount == 0 { // treat as EoF
if rc == 0 { // treat as EoF
break
}
ctx.table[ctx.hash] = ctx.input[i]
}
ctx.hash = (ctx.hash << 4) ^ uint16(ctx.input[i])
}
readCount = copy(output, ctx.input[:i])
rc = copy(output, ctx.input[:i])
total += rc
// Place any remaining bytes in the buffer
if uint(readCount) < i {
ctx.input = ctx.input[readCount:i]
if uint(rc) < i {
ctx.input = ctx.input[:copy(ctx.input, ctx.input[rc:i])]
} else {
ctx.input = ctx.input[:0]
}
return readCount, nil
return total, err
})
}
|