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+/*
+ * Copyright (c) 2003 The Regents of The University of Michigan
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @file
+ * LZSSCompression definitions.
+ */
+
+#include <assert.h>
+
+#include "lzss_compression.hh"
+
+#include "misc.hh" //for fatal
+
+int
+LZSSCompression::findSubString(uint8_t *src, int front, int back, int size)
+{
+ int subSize = 0;
+ int max_length = 2048;
+ if (size - back < max_length) {
+ max_length = size - back;
+ }
+ for (int i = 0; i < max_length; ++i) {
+ if (src[front+i] != src[back+i]) {
+ return subSize;
+ }
+ ++subSize;
+ }
+ return subSize;
+}
+
+int
+LZSSCompression::emitByte(uint8_t *dest, uint8_t byte)
+{
+ if ((byte >> 5 & 0x7) == 0 || (byte >> 5 & 0x7) == 7) {
+ // If the top 3 bits are the same, emit 00<6bits>
+ dest[0] = byte & 0x3f;
+ return 1;
+ } else {
+ // emit 01XXXXXX <8 bits>
+ dest[0] = 0x40;
+ dest[1] = byte;
+ return 2;
+ }
+}
+
+void
+LZSSCompression::emitString(uint8_t *dest, uint16_t P, uint16_t L)
+{
+ // Emit 1<7P> <5P><3L> <8L>
+ dest[0] = 1<<7 | (P >> 5 & 0x7f);
+ dest[1] = ((P & 0x1f) << 3) | (L>>8 & 0x3);
+ dest[2] = L & 0xFF;
+}
+
+int
+LZSSCompression::compress(uint8_t *dest, uint8_t *src, int size)
+{
+ if (size > 4096) {
+ fatal("Compression can only handle block sizes of 4096 bytes or less");
+ }
+
+ // Encode the first byte.
+ int dest_index = emitByte(dest, src[0]);
+ int i = 1;
+ // A 11 bit field
+ uint16_t L;
+ // A 12 bit field
+ uint16_t P = 0;
+
+ while (i < size && dest_index < size) {
+ L = 0;
+
+ if (dest_index+3 >= size) {
+ dest_index = size;
+ continue;
+ }
+
+ if (i == size - 1) {
+ // Output the character
+ dest_index += emitByte(&dest[dest_index], src[i]);
+ ++i;
+ continue;
+ }
+ for (int j = 0; j < i; ++j) {
+ int sub_size = findSubString(src, j, i, size);
+ if (sub_size >= L) {
+ L = sub_size;
+ P = j;
+ }
+ }
+ if (L > 1) {
+ // Output the string reference
+ emitString(&dest[dest_index], P, L);
+ dest_index += 3;
+ i = i+L;
+ } else {
+ // Output the character
+ dest_index += emitByte(&dest[dest_index], src[i]);
+ ++i;
+ }
+ }
+
+ if (dest_index >= size) {
+ // Have expansion instead of compression, just copy.
+ memcpy(dest,src,size);
+ return size;
+ }
+ return dest_index;
+}
+
+int
+LZSSCompression::uncompress(uint8_t *dest, uint8_t *src, int size)
+{
+ int index = 0;
+ int i = 0;
+ while (i < size) {
+ if (src[i] & 1<<7 ) {
+ // We have a string
+ // Extract P
+ int start = (src[i] & 0x3f)<<5 | ((src[i+1] >> 3) & 0x1f);
+ // Extract L
+ int len = (src[i+1] & 0x07)<<8 | src[i+2];
+ i += 3;
+ for (int j = start; j < start+len; ++j) {
+ dest[index++] = dest[j];
+ }
+ } else {
+ // We have a character
+ if (src[i] & 1<<6) {
+ // Value is in the next byte
+ dest[index++] = src[i+1];
+ i += 2;
+ } else {
+ // just extend the lower 6 bits
+ dest[index++] = (src[i] & 0x3f) | ((src[i] & 1<<5) ? 0xC0 : 0);
+ ++i;
+ }
+ }
+ }
+ return index;
+}