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1.1 misho 1: /* inffast.c -- fast decoding
2: * Copyright (C) 1995-2004 Mark Adler
3: * For conditions of distribution and use, see copyright notice in zlib.h
4: */
5:
6: #include "zutil.h"
7: #include "inftrees.h"
8: #include "inflate.h"
9: #include "inffast.h"
10:
11: #ifndef ASMINF
12:
13: /* Allow machine dependent optimization for post-increment or pre-increment.
14: Based on testing to date,
15: Pre-increment preferred for:
16: - PowerPC G3 (Adler)
17: - MIPS R5000 (Randers-Pehrson)
18: Post-increment preferred for:
19: - none
20: No measurable difference:
21: - Pentium III (Anderson)
22: - M68060 (Nikl)
23: */
24: #ifdef POSTINC
25: # define OFF 0
26: # define PUP(a) *(a)++
27: #else
28: # define OFF 1
29: # define PUP(a) *++(a)
30: #endif
31:
32: /*
33: Decode literal, length, and distance codes and write out the resulting
34: literal and match bytes until either not enough input or output is
35: available, an end-of-block is encountered, or a data error is encountered.
36: When large enough input and output buffers are supplied to inflate(), for
37: example, a 16K input buffer and a 64K output buffer, more than 95% of the
38: inflate execution time is spent in this routine.
39:
40: Entry assumptions:
41:
42: state->mode == LEN
43: strm->avail_in >= 6
44: strm->avail_out >= 258
45: start >= strm->avail_out
46: state->bits < 8
47:
48: On return, state->mode is one of:
49:
50: LEN -- ran out of enough output space or enough available input
51: TYPE -- reached end of block code, inflate() to interpret next block
52: BAD -- error in block data
53:
54: Notes:
55:
56: - The maximum input bits used by a length/distance pair is 15 bits for the
57: length code, 5 bits for the length extra, 15 bits for the distance code,
58: and 13 bits for the distance extra. This totals 48 bits, or six bytes.
59: Therefore if strm->avail_in >= 6, then there is enough input to avoid
60: checking for available input while decoding.
61:
62: - The maximum bytes that a single length/distance pair can output is 258
63: bytes, which is the maximum length that can be coded. inflate_fast()
64: requires strm->avail_out >= 258 for each loop to avoid checking for
65: output space.
66: */
67: void inflate_fast(strm, start)
68: z_streamp strm;
69: unsigned start; /* inflate()'s starting value for strm->avail_out */
70: {
71: struct inflate_state FAR *state;
72: unsigned char FAR *in; /* local strm->next_in */
73: unsigned char FAR *last; /* while in < last, enough input available */
74: unsigned char FAR *out; /* local strm->next_out */
75: unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
76: unsigned char FAR *end; /* while out < end, enough space available */
77: #ifdef INFLATE_STRICT
78: unsigned dmax; /* maximum distance from zlib header */
79: #endif
80: unsigned wsize; /* window size or zero if not using window */
81: unsigned whave; /* valid bytes in the window */
82: unsigned write; /* window write index */
83: unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
84: unsigned long hold; /* local strm->hold */
85: unsigned bits; /* local strm->bits */
86: code const FAR *lcode; /* local strm->lencode */
87: code const FAR *dcode; /* local strm->distcode */
88: unsigned lmask; /* mask for first level of length codes */
89: unsigned dmask; /* mask for first level of distance codes */
90: code this; /* retrieved table entry */
91: unsigned op; /* code bits, operation, extra bits, or */
92: /* window position, window bytes to copy */
93: unsigned len; /* match length, unused bytes */
94: unsigned dist; /* match distance */
95: unsigned char FAR *from; /* where to copy match from */
96:
97: /* copy state to local variables */
98: state = (struct inflate_state FAR *)strm->state;
99: in = strm->next_in - OFF;
100: last = in + (strm->avail_in - 5);
101: out = strm->next_out - OFF;
102: beg = out - (start - strm->avail_out);
103: end = out + (strm->avail_out - 257);
104: #ifdef INFLATE_STRICT
105: dmax = state->dmax;
106: #endif
107: wsize = state->wsize;
108: whave = state->whave;
109: write = state->write;
110: window = state->window;
111: hold = state->hold;
112: bits = state->bits;
113: lcode = state->lencode;
114: dcode = state->distcode;
115: lmask = (1U << state->lenbits) - 1;
116: dmask = (1U << state->distbits) - 1;
117:
118: /* decode literals and length/distances until end-of-block or not enough
119: input data or output space */
120: do {
121: if (bits < 15) {
122: hold += (unsigned long)(PUP(in)) << bits;
123: bits += 8;
124: hold += (unsigned long)(PUP(in)) << bits;
125: bits += 8;
126: }
127: this = lcode[hold & lmask];
128: dolen:
129: op = (unsigned)(this.bits);
130: hold >>= op;
131: bits -= op;
132: op = (unsigned)(this.op);
133: if (op == 0) { /* literal */
134: Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
135: "inflate: literal '%c'\n" :
136: "inflate: literal 0x%02x\n", this.val));
137: PUP(out) = (unsigned char)(this.val);
138: }
139: else if (op & 16) { /* length base */
140: len = (unsigned)(this.val);
141: op &= 15; /* number of extra bits */
142: if (op) {
143: if (bits < op) {
144: hold += (unsigned long)(PUP(in)) << bits;
145: bits += 8;
146: }
147: len += (unsigned)hold & ((1U << op) - 1);
148: hold >>= op;
149: bits -= op;
150: }
151: Tracevv((stderr, "inflate: length %u\n", len));
152: if (bits < 15) {
153: hold += (unsigned long)(PUP(in)) << bits;
154: bits += 8;
155: hold += (unsigned long)(PUP(in)) << bits;
156: bits += 8;
157: }
158: this = dcode[hold & dmask];
159: dodist:
160: op = (unsigned)(this.bits);
161: hold >>= op;
162: bits -= op;
163: op = (unsigned)(this.op);
164: if (op & 16) { /* distance base */
165: dist = (unsigned)(this.val);
166: op &= 15; /* number of extra bits */
167: if (bits < op) {
168: hold += (unsigned long)(PUP(in)) << bits;
169: bits += 8;
170: if (bits < op) {
171: hold += (unsigned long)(PUP(in)) << bits;
172: bits += 8;
173: }
174: }
175: dist += (unsigned)hold & ((1U << op) - 1);
176: #ifdef INFLATE_STRICT
177: if (dist > dmax) {
178: strm->msg = (char *)"invalid distance too far back";
179: state->mode = BAD;
180: break;
181: }
182: #endif
183: hold >>= op;
184: bits -= op;
185: Tracevv((stderr, "inflate: distance %u\n", dist));
186: op = (unsigned)(out - beg); /* max distance in output */
187: if (dist > op) { /* see if copy from window */
188: op = dist - op; /* distance back in window */
189: if (op > whave) {
190: strm->msg = (char *)"invalid distance too far back";
191: state->mode = BAD;
192: break;
193: }
194: from = window - OFF;
195: if (write == 0) { /* very common case */
196: from += wsize - op;
197: if (op < len) { /* some from window */
198: len -= op;
199: do {
200: PUP(out) = PUP(from);
201: } while (--op);
202: from = out - dist; /* rest from output */
203: }
204: }
205: else if (write < op) { /* wrap around window */
206: from += wsize + write - op;
207: op -= write;
208: if (op < len) { /* some from end of window */
209: len -= op;
210: do {
211: PUP(out) = PUP(from);
212: } while (--op);
213: from = window - OFF;
214: if (write < len) { /* some from start of window */
215: op = write;
216: len -= op;
217: do {
218: PUP(out) = PUP(from);
219: } while (--op);
220: from = out - dist; /* rest from output */
221: }
222: }
223: }
224: else { /* contiguous in window */
225: from += write - op;
226: if (op < len) { /* some from window */
227: len -= op;
228: do {
229: PUP(out) = PUP(from);
230: } while (--op);
231: from = out - dist; /* rest from output */
232: }
233: }
234: while (len > 2) {
235: PUP(out) = PUP(from);
236: PUP(out) = PUP(from);
237: PUP(out) = PUP(from);
238: len -= 3;
239: }
240: if (len) {
241: PUP(out) = PUP(from);
242: if (len > 1)
243: PUP(out) = PUP(from);
244: }
245: }
246: else {
247: from = out - dist; /* copy direct from output */
248: do { /* minimum length is three */
249: PUP(out) = PUP(from);
250: PUP(out) = PUP(from);
251: PUP(out) = PUP(from);
252: len -= 3;
253: } while (len > 2);
254: if (len) {
255: PUP(out) = PUP(from);
256: if (len > 1)
257: PUP(out) = PUP(from);
258: }
259: }
260: }
261: else if ((op & 64) == 0) { /* 2nd level distance code */
262: this = dcode[this.val + (hold & ((1U << op) - 1))];
263: goto dodist;
264: }
265: else {
266: strm->msg = (char *)"invalid distance code";
267: state->mode = BAD;
268: break;
269: }
270: }
271: else if ((op & 64) == 0) { /* 2nd level length code */
272: this = lcode[this.val + (hold & ((1U << op) - 1))];
273: goto dolen;
274: }
275: else if (op & 32) { /* end-of-block */
276: Tracevv((stderr, "inflate: end of block\n"));
277: state->mode = TYPE;
278: break;
279: }
280: else {
281: strm->msg = (char *)"invalid literal/length code";
282: state->mode = BAD;
283: break;
284: }
285: } while (in < last && out < end);
286:
287: /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
288: len = bits >> 3;
289: in -= len;
290: bits -= len << 3;
291: hold &= (1U << bits) - 1;
292:
293: /* update state and return */
294: strm->next_in = in + OFF;
295: strm->next_out = out + OFF;
296: strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
297: strm->avail_out = (unsigned)(out < end ?
298: 257 + (end - out) : 257 - (out - end));
299: state->hold = hold;
300: state->bits = bits;
301: return;
302: }
303:
304: /*
305: inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
306: - Using bit fields for code structure
307: - Different op definition to avoid & for extra bits (do & for table bits)
308: - Three separate decoding do-loops for direct, window, and write == 0
309: - Special case for distance > 1 copies to do overlapped load and store copy
310: - Explicit branch predictions (based on measured branch probabilities)
311: - Deferring match copy and interspersed it with decoding subsequent codes
312: - Swapping literal/length else
313: - Swapping window/direct else
314: - Larger unrolled copy loops (three is about right)
315: - Moving len -= 3 statement into middle of loop
316: */
317:
318: #endif /* !ASMINF */