1 files changed, 166 insertions, 0 deletions
diff --git a/sim/cache/lzss_compression.cc b/sim/cache/lzss_compression.cc
new file mode 100644
index 000000000..a1933215a
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+++ b/sim/cache/lzss_compression.cc
@@ -0,0 +1,166 @@
+/*
+ * 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;
+}