1*0Sstevel@tonic-gate /*
2*0Sstevel@tonic-gate * CDDL HEADER START
3*0Sstevel@tonic-gate *
4*0Sstevel@tonic-gate * The contents of this file are subject to the terms of the
5*0Sstevel@tonic-gate * Common Development and Distribution License, Version 1.0 only
6*0Sstevel@tonic-gate * (the "License"). You may not use this file except in compliance
7*0Sstevel@tonic-gate * with the License.
8*0Sstevel@tonic-gate *
9*0Sstevel@tonic-gate * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10*0Sstevel@tonic-gate * or http://www.opensolaris.org/os/licensing.
11*0Sstevel@tonic-gate * See the License for the specific language governing permissions
12*0Sstevel@tonic-gate * and limitations under the License.
13*0Sstevel@tonic-gate *
14*0Sstevel@tonic-gate * When distributing Covered Code, include this CDDL HEADER in each
15*0Sstevel@tonic-gate * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16*0Sstevel@tonic-gate * If applicable, add the following below this CDDL HEADER, with the
17*0Sstevel@tonic-gate * fields enclosed by brackets "[]" replaced with your own identifying
18*0Sstevel@tonic-gate * information: Portions Copyright [yyyy] [name of copyright owner]
19*0Sstevel@tonic-gate *
20*0Sstevel@tonic-gate * CDDL HEADER END
21*0Sstevel@tonic-gate */
22*0Sstevel@tonic-gate /*
23*0Sstevel@tonic-gate * Copyright (c) 1998 by Sun Microsystems, Inc.
24*0Sstevel@tonic-gate * All rights reserved.
25*0Sstevel@tonic-gate */
26*0Sstevel@tonic-gate
27*0Sstevel@tonic-gate #pragma ident "%Z%%M% %I% %E% SMI"
28*0Sstevel@tonic-gate
29*0Sstevel@tonic-gate /*
30*0Sstevel@tonic-gate * NOTE: this file is compiled into the kernel, cprboot, and savecore.
31*0Sstevel@tonic-gate * Therefore it must compile in kernel, boot, and userland source context;
32*0Sstevel@tonic-gate * so if you ever change this code, avoid references to external symbols.
33*0Sstevel@tonic-gate *
34*0Sstevel@tonic-gate * This compression algorithm is a derivative of LZRW1, which I'll call
35*0Sstevel@tonic-gate * LZJB in the classic LZ* spirit. All LZ* (Lempel-Ziv) algorithms are
36*0Sstevel@tonic-gate * based on the same basic principle: when a "phrase" (sequences of bytes)
37*0Sstevel@tonic-gate * is repeated in a data stream, we can save space by storing a reference to
38*0Sstevel@tonic-gate * the previous instance of that phrase (a "copy item") rather than storing
39*0Sstevel@tonic-gate * the phrase itself (a "literal item"). The compressor remembers phrases
40*0Sstevel@tonic-gate * in a simple hash table (the "Lempel history") that maps three-character
41*0Sstevel@tonic-gate * sequences (the minimum match) to the addresses where they were last seen.
42*0Sstevel@tonic-gate *
43*0Sstevel@tonic-gate * A copy item must encode both the length and the location of the matching
44*0Sstevel@tonic-gate * phrase so that decompress() can reconstruct the original data stream.
45*0Sstevel@tonic-gate * For example, here's how we'd encode "yadda yadda yadda, blah blah blah"
46*0Sstevel@tonic-gate * (with "_" replacing spaces for readability):
47*0Sstevel@tonic-gate *
48*0Sstevel@tonic-gate * Original:
49*0Sstevel@tonic-gate *
50*0Sstevel@tonic-gate * y a d d a _ y a d d a _ y a d d a , _ b l a h _ b l a h _ b l a h
51*0Sstevel@tonic-gate *
52*0Sstevel@tonic-gate * Compressed:
53*0Sstevel@tonic-gate *
54*0Sstevel@tonic-gate * y a d d a _ 6 11 , _ b l a h 5 10
55*0Sstevel@tonic-gate *
56*0Sstevel@tonic-gate * In the compressed output, the "6 11" simply means "to get the original
57*0Sstevel@tonic-gate * data, execute memmove(ptr, ptr - 6, 11)". Note that in this example,
58*0Sstevel@tonic-gate * the match at "6 11" actually extends beyond the current location and
59*0Sstevel@tonic-gate * overlaps it. That's OK; like memmove(), decompress() handles overlap.
60*0Sstevel@tonic-gate *
61*0Sstevel@tonic-gate * There's still one more thing decompress() needs to know, which is how to
62*0Sstevel@tonic-gate * distinguish literal items from copy items. We encode this information
63*0Sstevel@tonic-gate * in an 8-bit bitmap that precedes each 8 items of output; if the Nth bit
64*0Sstevel@tonic-gate * is set, then the Nth item is a copy item. Thus the full encoding for
65*0Sstevel@tonic-gate * the example above would be:
66*0Sstevel@tonic-gate *
67*0Sstevel@tonic-gate * 0x40 y a d d a _ 6 11 , 0x20 _ b l a h 5 10
68*0Sstevel@tonic-gate *
69*0Sstevel@tonic-gate * Finally, the "6 11" isn't really encoded as the two byte values 6 and 11
70*0Sstevel@tonic-gate * in the output stream because, empirically, we get better compression by
71*0Sstevel@tonic-gate * dedicating more bits to offset, fewer to match length. LZJB uses 6 bits
72*0Sstevel@tonic-gate * to encode the match length, 10 bits to encode the offset. Since copy-item
73*0Sstevel@tonic-gate * encoding consumes 2 bytes, we don't generate copy items unless the match
74*0Sstevel@tonic-gate * length is at least 3; therefore, we can store (length - 3) in the 6-bit
75*0Sstevel@tonic-gate * match length field, which extends the maximum match from 63 to 66 bytes.
76*0Sstevel@tonic-gate * Thus the 2-byte encoding for a copy item is as follows:
77*0Sstevel@tonic-gate *
78*0Sstevel@tonic-gate * byte[0] = ((length - 3) << 2) | (offset >> 8);
79*0Sstevel@tonic-gate * byte[1] = (uint8_t)offset;
80*0Sstevel@tonic-gate *
81*0Sstevel@tonic-gate * In our example above, an offset of 6 with length 11 would be encoded as:
82*0Sstevel@tonic-gate *
83*0Sstevel@tonic-gate * byte[0] = ((11 - 3) << 2) | (6 >> 8) = 0x20
84*0Sstevel@tonic-gate * byte[1] = (uint8_t)6 = 0x6
85*0Sstevel@tonic-gate *
86*0Sstevel@tonic-gate * Similarly, an offset of 5 with length 10 would be encoded as:
87*0Sstevel@tonic-gate *
88*0Sstevel@tonic-gate * byte[0] = ((10 - 3) << 2) | (5 >> 8) = 0x1c
89*0Sstevel@tonic-gate * byte[1] = (uint8_t)5 = 0x5
90*0Sstevel@tonic-gate *
91*0Sstevel@tonic-gate * Putting it all together, the actual LZJB output for our example is:
92*0Sstevel@tonic-gate *
93*0Sstevel@tonic-gate * 0x40 y a d d a _ 0x2006 , 0x20 _ b l a h 0x1c05
94*0Sstevel@tonic-gate *
95*0Sstevel@tonic-gate * The main differences between LZRW1 and LZJB are as follows:
96*0Sstevel@tonic-gate *
97*0Sstevel@tonic-gate * (1) LZRW1 is sloppy about buffer overruns. LZJB never reads past the
98*0Sstevel@tonic-gate * end of its input, and never writes past the end of its output.
99*0Sstevel@tonic-gate *
100*0Sstevel@tonic-gate * (2) LZJB allows a maximum match length of 66 (vs. 18 for LZRW1), with
101*0Sstevel@tonic-gate * the trade-off being a shorter look-behind (1K vs. 4K for LZRW1).
102*0Sstevel@tonic-gate *
103*0Sstevel@tonic-gate * (3) LZJB records only the low-order 16 bits of pointers in the Lempel
104*0Sstevel@tonic-gate * history (which is all we need since the maximum look-behind is 1K),
105*0Sstevel@tonic-gate * and uses only 256 hash entries (vs. 4096 for LZRW1). This makes
106*0Sstevel@tonic-gate * the compression hash small enough to allocate on the stack, which
107*0Sstevel@tonic-gate * solves two problems: (1) it saves 64K of kernel/cprboot memory,
108*0Sstevel@tonic-gate * and (2) it makes the code MT-safe without any locking, since we
109*0Sstevel@tonic-gate * don't have multiple threads sharing a common hash table.
110*0Sstevel@tonic-gate *
111*0Sstevel@tonic-gate * (4) LZJB is faster at both compression and decompression, has a
112*0Sstevel@tonic-gate * better compression ratio, and is somewhat simpler than LZRW1.
113*0Sstevel@tonic-gate *
114*0Sstevel@tonic-gate * Finally, note that LZJB is non-deterministic: given the same input,
115*0Sstevel@tonic-gate * two calls to compress() may produce different output. This is a
116*0Sstevel@tonic-gate * general characteristic of most Lempel-Ziv derivatives because there's
117*0Sstevel@tonic-gate * no need to initialize the Lempel history; not doing so saves time.
118*0Sstevel@tonic-gate */
119*0Sstevel@tonic-gate
120*0Sstevel@tonic-gate #include <sys/types.h>
121*0Sstevel@tonic-gate
122*0Sstevel@tonic-gate #define MATCH_BITS 6
123*0Sstevel@tonic-gate #define MATCH_MIN 3
124*0Sstevel@tonic-gate #define MATCH_MAX ((1 << MATCH_BITS) + (MATCH_MIN - 1))
125*0Sstevel@tonic-gate #define OFFSET_MASK ((1 << (16 - MATCH_BITS)) - 1)
126*0Sstevel@tonic-gate #define LEMPEL_SIZE 256
127*0Sstevel@tonic-gate
128*0Sstevel@tonic-gate size_t
compress(void * s_start,void * d_start,size_t s_len)129*0Sstevel@tonic-gate compress(void *s_start, void *d_start, size_t s_len)
130*0Sstevel@tonic-gate {
131*0Sstevel@tonic-gate uchar_t *src = s_start;
132*0Sstevel@tonic-gate uchar_t *dst = d_start;
133*0Sstevel@tonic-gate uchar_t *cpy, *copymap;
134*0Sstevel@tonic-gate int copymask = 1 << (NBBY - 1);
135*0Sstevel@tonic-gate int mlen, offset;
136*0Sstevel@tonic-gate uint16_t *hp;
137*0Sstevel@tonic-gate uint16_t lempel[LEMPEL_SIZE]; /* uninitialized; see above */
138*0Sstevel@tonic-gate
139*0Sstevel@tonic-gate while (src < (uchar_t *)s_start + s_len) {
140*0Sstevel@tonic-gate if ((copymask <<= 1) == (1 << NBBY)) {
141*0Sstevel@tonic-gate if (dst >= (uchar_t *)d_start + s_len - 1 - 2 * NBBY) {
142*0Sstevel@tonic-gate mlen = s_len;
143*0Sstevel@tonic-gate for (src = s_start, dst = d_start; mlen; mlen--)
144*0Sstevel@tonic-gate *dst++ = *src++;
145*0Sstevel@tonic-gate return (s_len);
146*0Sstevel@tonic-gate }
147*0Sstevel@tonic-gate copymask = 1;
148*0Sstevel@tonic-gate copymap = dst;
149*0Sstevel@tonic-gate *dst++ = 0;
150*0Sstevel@tonic-gate }
151*0Sstevel@tonic-gate if (src > (uchar_t *)s_start + s_len - MATCH_MAX) {
152*0Sstevel@tonic-gate *dst++ = *src++;
153*0Sstevel@tonic-gate continue;
154*0Sstevel@tonic-gate }
155*0Sstevel@tonic-gate hp = &lempel[((src[0] + 13) ^ (src[1] - 13) ^ src[2]) &
156*0Sstevel@tonic-gate (LEMPEL_SIZE - 1)];
157*0Sstevel@tonic-gate offset = (intptr_t)(src - *hp) & OFFSET_MASK;
158*0Sstevel@tonic-gate *hp = (uint16_t)(uintptr_t)src;
159*0Sstevel@tonic-gate cpy = src - offset;
160*0Sstevel@tonic-gate if (cpy >= (uchar_t *)s_start && cpy != src &&
161*0Sstevel@tonic-gate src[0] == cpy[0] && src[1] == cpy[1] && src[2] == cpy[2]) {
162*0Sstevel@tonic-gate *copymap |= copymask;
163*0Sstevel@tonic-gate for (mlen = MATCH_MIN; mlen < MATCH_MAX; mlen++)
164*0Sstevel@tonic-gate if (src[mlen] != cpy[mlen])
165*0Sstevel@tonic-gate break;
166*0Sstevel@tonic-gate *dst++ = ((mlen - MATCH_MIN) << (NBBY - MATCH_BITS)) |
167*0Sstevel@tonic-gate (offset >> NBBY);
168*0Sstevel@tonic-gate *dst++ = (uchar_t)offset;
169*0Sstevel@tonic-gate src += mlen;
170*0Sstevel@tonic-gate } else {
171*0Sstevel@tonic-gate *dst++ = *src++;
172*0Sstevel@tonic-gate }
173*0Sstevel@tonic-gate }
174*0Sstevel@tonic-gate return (dst - (uchar_t *)d_start);
175*0Sstevel@tonic-gate }
176*0Sstevel@tonic-gate
177*0Sstevel@tonic-gate size_t
decompress(void * s_start,void * d_start,size_t s_len,size_t d_len)178*0Sstevel@tonic-gate decompress(void *s_start, void *d_start, size_t s_len, size_t d_len)
179*0Sstevel@tonic-gate {
180*0Sstevel@tonic-gate uchar_t *src = s_start;
181*0Sstevel@tonic-gate uchar_t *dst = d_start;
182*0Sstevel@tonic-gate uchar_t *s_end = (uchar_t *)s_start + s_len;
183*0Sstevel@tonic-gate uchar_t *d_end = (uchar_t *)d_start + d_len;
184*0Sstevel@tonic-gate uchar_t *cpy, copymap;
185*0Sstevel@tonic-gate int copymask = 1 << (NBBY - 1);
186*0Sstevel@tonic-gate
187*0Sstevel@tonic-gate if (s_len >= d_len) {
188*0Sstevel@tonic-gate size_t d_rem = d_len;
189*0Sstevel@tonic-gate while (d_rem-- != 0)
190*0Sstevel@tonic-gate *dst++ = *src++;
191*0Sstevel@tonic-gate return (d_len);
192*0Sstevel@tonic-gate }
193*0Sstevel@tonic-gate
194*0Sstevel@tonic-gate while (src < s_end && dst < d_end) {
195*0Sstevel@tonic-gate if ((copymask <<= 1) == (1 << NBBY)) {
196*0Sstevel@tonic-gate copymask = 1;
197*0Sstevel@tonic-gate copymap = *src++;
198*0Sstevel@tonic-gate }
199*0Sstevel@tonic-gate if (copymap & copymask) {
200*0Sstevel@tonic-gate int mlen = (src[0] >> (NBBY - MATCH_BITS)) + MATCH_MIN;
201*0Sstevel@tonic-gate int offset = ((src[0] << NBBY) | src[1]) & OFFSET_MASK;
202*0Sstevel@tonic-gate src += 2;
203*0Sstevel@tonic-gate if ((cpy = dst - offset) >= (uchar_t *)d_start)
204*0Sstevel@tonic-gate while (--mlen >= 0 && dst < d_end)
205*0Sstevel@tonic-gate *dst++ = *cpy++;
206*0Sstevel@tonic-gate else
207*0Sstevel@tonic-gate /*
208*0Sstevel@tonic-gate * offset before start of destination buffer
209*0Sstevel@tonic-gate * indicates corrupt source data
210*0Sstevel@tonic-gate */
211*0Sstevel@tonic-gate return (dst - (uchar_t *)d_start);
212*0Sstevel@tonic-gate } else {
213*0Sstevel@tonic-gate *dst++ = *src++;
214*0Sstevel@tonic-gate }
215*0Sstevel@tonic-gate }
216*0Sstevel@tonic-gate return (dst - (uchar_t *)d_start);
217*0Sstevel@tonic-gate }
218*0Sstevel@tonic-gate
219*0Sstevel@tonic-gate uint32_t
checksum32(void * cp_arg,size_t length)220*0Sstevel@tonic-gate checksum32(void *cp_arg, size_t length)
221*0Sstevel@tonic-gate {
222*0Sstevel@tonic-gate uchar_t *cp, *ep;
223*0Sstevel@tonic-gate uint32_t sum = 0;
224*0Sstevel@tonic-gate
225*0Sstevel@tonic-gate for (cp = cp_arg, ep = cp + length; cp < ep; cp++)
226*0Sstevel@tonic-gate sum = ((sum >> 1) | (sum << 31)) + *cp;
227*0Sstevel@tonic-gate return (sum);
228*0Sstevel@tonic-gate }
229