/src/zlib/inffast.c

Source
/* inffast.c -- fast decoding
 * Copyright (C) 1995-2025 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

#include "zutil.h"
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"

#ifdef ASMINF
#  pragma message("Assembler code may have bugs -- use at your own risk")
#else

/*
   Decode literal, length, and distance codes and write out the resulting
   literal and match bytes until either not enough input or output is
   available, an end-of-block is encountered, or a data error is encountered.
   When large enough input and output buffers are supplied to inflate(), for
   example, a 16K input buffer and a 64K output buffer, more than 95% of the
   inflate execution time is spent in this routine.

   Entry assumptions:

        state->mode == LEN
        strm->avail_in >= 6
        strm->avail_out >= 258
        start >= strm->avail_out
        state->bits < 8

   On return, state->mode is one of:

        LEN -- ran out of enough output space or enough available input
        TYPE -- reached end of block code, inflate() to interpret next block
        BAD -- error in block data

   Notes:

    - The maximum input bits used by a length/distance pair is 15 bits for the
      length code, 5 bits for the length extra, 15 bits for the distance code,
      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
      Therefore if strm->avail_in >= 6, then there is enough input to avoid
      checking for available input while decoding.

    - The maximum bytes that a single length/distance pair can output is 258
      bytes, which is the maximum length that can be coded.  inflate_fast()
      requires strm->avail_out >= 258 for each loop to avoid checking for
      output space.
 */
void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
    struct inflate_state FAR *state;
    z_const unsigned char FAR *in;      /* local strm->next_in */
    z_const unsigned char FAR *last;    /* have enough input while in < last */
    unsigned char FAR *out;     /* local strm->next_out */
    unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
    unsigned char FAR *end;     /* while out < end, enough space available */
#ifdef INFLATE_STRICT
    unsigned dmax;              /* maximum distance from zlib header */
#endif
    unsigned wsize;             /* window size or zero if not using window */
    unsigned whave;             /* valid bytes in the window */
    unsigned wnext;             /* window write index */
    unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
    unsigned long hold;         /* local strm->hold */
    unsigned bits;              /* local strm->bits */
    code const FAR *lcode;      /* local strm->lencode */
    code const FAR *dcode;      /* local strm->distcode */
    unsigned lmask;             /* mask for first level of length codes */
    unsigned dmask;             /* mask for first level of distance codes */
    code const *here;           /* retrieved table entry */
    unsigned op;                /* code bits, operation, extra bits, or */
                                /*  window position, window bytes to copy */
    unsigned len;               /* match length, unused bytes */
    unsigned dist;              /* match distance */
    unsigned char FAR *from;    /* where to copy match from */

    /* copy state to local variables */
    state = (struct inflate_state FAR *)strm->state;
    in = strm->next_in;
    last = in + (strm->avail_in - 5);
    out = strm->next_out;
    beg = out - (start - strm->avail_out);
    end = out + (strm->avail_out - 257);
#ifdef INFLATE_STRICT
    dmax = state->dmax;
#endif
    wsize = state->wsize;
    whave = state->whave;
    wnext = state->wnext;
    window = state->window;
    hold = state->hold;
    bits = state->bits;
    lcode = state->lencode;
    dcode = state->distcode;
    lmask = (1U << state->lenbits) - 1;
    dmask = (1U << state->distbits) - 1;

    /* decode literals and length/distances until end-of-block or not enough
       input data or output space */
    do {
        if (bits < 15) {
            hold += (unsigned long)(*in++) << bits;
            bits += 8;
            hold += (unsigned long)(*in++) << bits;
            bits += 8;
        }
        here = lcode + (hold & lmask);
      dolen:
        op = (unsigned)(here->bits);
        hold >>= op;
        bits -= op;
        op = (unsigned)(here->op);
        if (op == 0) {                          /* literal */
            Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?
                    "inflate:         literal '%c'\n" :
                    "inflate:         literal 0x%02x\n", here->val));
            *out++ = (unsigned char)(here->val);
        }
        else if (op & 16) {                     /* length base */
            len = (unsigned)(here->val);
            op &= 15;                           /* number of extra bits */
            if (op) {
                if (bits < op) {
                    hold += (unsigned long)(*in++) << bits;
                    bits += 8;
                }
                len += (unsigned)hold & ((1U << op) - 1);
                hold >>= op;
                bits -= op;
            }
            Tracevv((stderr, "inflate:         length %u\n", len));
            if (bits < 15) {
                hold += (unsigned long)(*in++) << bits;
                bits += 8;
                hold += (unsigned long)(*in++) << bits;
                bits += 8;
            }
            here = dcode + (hold & dmask);
          dodist:
            op = (unsigned)(here->bits);
            hold >>= op;
            bits -= op;
            op = (unsigned)(here->op);
            if (op & 16) {                      /* distance base */
                dist = (unsigned)(here->val);
                op &= 15;                       /* number of extra bits */
                if (bits < op) {
                    hold += (unsigned long)(*in++) << bits;
                    bits += 8;
                    if (bits < op) {
                        hold += (unsigned long)(*in++) << bits;
                        bits += 8;
                    }
                }
                dist += (unsigned)hold & ((1U << op) - 1);
#ifdef INFLATE_STRICT
                if (dist > dmax) {
                    strm->msg = (z_const char *)
                        "invalid distance too far back";
                    state->mode = BAD;
                    break;
                }
#endif
                hold >>= op;
                bits -= op;
                Tracevv((stderr, "inflate:         distance %u\n", dist));
                op = (unsigned)(out - beg);     /* max distance in output */
                if (dist > op) {                /* see if copy from window */
                    op = dist - op;             /* distance back in window */
                    if (op > whave) {
                        if (state->sane) {
                            strm->msg = (z_const char *)
                                "invalid distance too far back";
                            state->mode = BAD;
                            break;
                        }
#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
                        if (len <= op - whave) {
                            do {
                                *out++ = 0;
                            } while (--len);
                            continue;
                        }
                        len -= op - whave;
                        do {
                            *out++ = 0;
                        } while (--op > whave);
                        if (op == 0) {
                            from = out - dist;
                            do {
                                *out++ = *from++;
                            } while (--len);
                            continue;
                        }
#endif
                    }
                    from = window;
                    if (wnext == 0) {           /* very common case */
                        from += wsize - op;
                        if (op < len) {         /* some from window */
                            len -= op;
                            do {
                                *out++ = *from++;
                            } while (--op);
                            from = out - dist;  /* rest from output */
                        }
                    }
                    else if (wnext < op) {      /* wrap around window */
                        from += wsize + wnext - op;
                        op -= wnext;
                        if (op < len) {         /* some from end of window */
                            len -= op;
                            do {
                                *out++ = *from++;
                            } while (--op);
                            from = window;
                            if (wnext < len) {  /* some from start of window */
                                op = wnext;
                                len -= op;
                                do {
                                    *out++ = *from++;
                                } while (--op);
                                from = out - dist;      /* rest from output */
                            }
                        }
                    }
                    else {                      /* contiguous in window */
                        from += wnext - op;
                        if (op < len) {         /* some from window */
                            len -= op;
                            do {
                                *out++ = *from++;
                            } while (--op);
                            from = out - dist;  /* rest from output */
                        }
                    }
                    while (len > 2) {
                        *out++ = *from++;
                        *out++ = *from++;
                        *out++ = *from++;
                        len -= 3;
                    }
                    if (len) {
                        *out++ = *from++;
                        if (len > 1)
                            *out++ = *from++;
                    }
                }
                else {
                    from = out - dist;          /* copy direct from output */
                    do {                        /* minimum length is three */
                        *out++ = *from++;
                        *out++ = *from++;
                        *out++ = *from++;
                        len -= 3;
                    } while (len > 2);
                    if (len) {
                        *out++ = *from++;
                        if (len > 1)
                            *out++ = *from++;
                    }
                }
            }
            else if ((op & 64) == 0) {          /* 2nd level distance code */
                here = dcode + here->val + (hold & ((1U << op) - 1));
                goto dodist;
            }
            else {
                strm->msg = (z_const char *)"invalid distance code";
                state->mode = BAD;
                break;
            }
        }
        else if ((op & 64) == 0) {              /* 2nd level length code */
            here = lcode + here->val + (hold & ((1U << op) - 1));
            goto dolen;
        }
        else if (op & 32) {                     /* end-of-block */
            Tracevv((stderr, "inflate:         end of block\n"));
            state->mode = TYPE;
            break;
        }
        else {
            strm->msg = (z_const char *)"invalid literal/length code";
            state->mode = BAD;
            break;
        }
    } while (in < last && out < end);

    /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
    len = bits >> 3;
    in -= len;
    bits -= len << 3;
    hold &= (1U << bits) - 1;

    /* update state and return */
    strm->next_in = in;
    strm->next_out = out;
    strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
    strm->avail_out = (unsigned)(out < end ?
                                 257 + (end - out) : 257 - (out - end));
    state->hold = hold;
    state->bits = bits;
    return;
}

/*
   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
   - Using bit fields for code structure
   - Different op definition to avoid & for extra bits (do & for table bits)
   - Three separate decoding do-loops for direct, window, and wnext == 0
   - Special case for distance > 1 copies to do overlapped load and store copy
   - Explicit branch predictions (based on measured branch probabilities)
   - Deferring match copy and interspersed it with decoding subsequent codes
   - Swapping literal/length else
   - Swapping window/direct else
   - Larger unrolled copy loops (three is about right)
   - Moving len -= 3 statement into middle of loop
 */

#endif /* !ASMINF */

Coverage Report

Created: 2026-01-17 06:31

Line	Count	Source
1		/* inffast.c -- fast decoding
2		* Copyright (C) 1995-2025 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		#ifdef ASMINF
12		# pragma message("Assembler code may have bugs -- use at your own risk")
13		#else
14
15		/*
16		Decode literal, length, and distance codes and write out the resulting
17		literal and match bytes until either not enough input or output is
18		available, an end-of-block is encountered, or a data error is encountered.
19		When large enough input and output buffers are supplied to inflate(), for
20		example, a 16K input buffer and a 64K output buffer, more than 95% of the
21		inflate execution time is spent in this routine.
22
23		Entry assumptions:
24
25		state->mode == LEN
26		strm->avail_in >= 6
27		strm->avail_out >= 258
28		start >= strm->avail_out
29		state->bits < 8
30
31		On return, state->mode is one of:
32
33		LEN -- ran out of enough output space or enough available input
34		TYPE -- reached end of block code, inflate() to interpret next block
35		BAD -- error in block data
36
37		Notes:
38
39		- The maximum input bits used by a length/distance pair is 15 bits for the
40		length code, 5 bits for the length extra, 15 bits for the distance code,
41		and 13 bits for the distance extra. This totals 48 bits, or six bytes.
42		Therefore if strm->avail_in >= 6, then there is enough input to avoid
43		checking for available input while decoding.
44
45		- The maximum bytes that a single length/distance pair can output is 258
46		bytes, which is the maximum length that can be coded. inflate_fast()
47		requires strm->avail_out >= 258 for each loop to avoid checking for
48		output space.
49		*/
50	79.5k	void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
51	79.5k	struct inflate_state FAR *state;
52	79.5k	z_const unsigned char FAR in; / local strm->next_in */
53	79.5k	z_const unsigned char FAR last; / have enough input while in < last */
54	79.5k	unsigned char FAR out; / local strm->next_out */
55	79.5k	unsigned char FAR beg; / inflate()'s initial strm->next_out */
56	79.5k	unsigned char FAR end; / while out < end, enough space available */
57		#ifdef INFLATE_STRICT
58		unsigned dmax; /* maximum distance from zlib header */
59		#endif
60	79.5k	unsigned wsize; /* window size or zero if not using window */
61	79.5k	unsigned whave; /* valid bytes in the window */
62	79.5k	unsigned wnext; /* window write index */
63	79.5k	unsigned char FAR window; / allocated sliding window, if wsize != 0 */
64	79.5k	unsigned long hold; /* local strm->hold */
65	79.5k	unsigned bits; /* local strm->bits */
66	79.5k	code const FAR lcode; / local strm->lencode */
67	79.5k	code const FAR dcode; / local strm->distcode */
68	79.5k	unsigned lmask; /* mask for first level of length codes */
69	79.5k	unsigned dmask; /* mask for first level of distance codes */
70	79.5k	code const here; / retrieved table entry */
71	79.5k	unsigned op; /* code bits, operation, extra bits, or */
72		/* window position, window bytes to copy */
73	79.5k	unsigned len; /* match length, unused bytes */
74	79.5k	unsigned dist; /* match distance */
75	79.5k	unsigned char FAR from; / where to copy match from */
76
77		/* copy state to local variables */
78	79.5k	state = (struct inflate_state FAR *)strm->state;
79	79.5k	in = strm->next_in;
80	79.5k	last = in + (strm->avail_in - 5);
81	79.5k	out = strm->next_out;
82	79.5k	beg = out - (start - strm->avail_out);
83	79.5k	end = out + (strm->avail_out - 257);
84		#ifdef INFLATE_STRICT
85		dmax = state->dmax;
86		#endif
87	79.5k	wsize = state->wsize;
88	79.5k	whave = state->whave;
89	79.5k	wnext = state->wnext;
90	79.5k	window = state->window;
91	79.5k	hold = state->hold;
92	79.5k	bits = state->bits;
93	79.5k	lcode = state->lencode;
94	79.5k	dcode = state->distcode;
95	79.5k	lmask = (1U << state->lenbits) - 1;
96	79.5k	dmask = (1U << state->distbits) - 1;
97
98		/* decode literals and length/distances until end-of-block or not enough
99		input data or output space */
100	5.27M	do {
101	5.27M	if (bits < 15) {
102	2.48M	hold += (unsigned long)(*in++) << bits;
103	2.48M	bits += 8;
104	2.48M	hold += (unsigned long)(*in++) << bits;
105	2.48M	bits += 8;
106	2.48M	}
107	5.27M	here = lcode + (hold & lmask);
108	5.54M	dolen:
109	5.54M	op = (unsigned)(here->bits);
110	5.54M	hold >>= op;
111	5.54M	bits -= op;
112	5.54M	op = (unsigned)(here->op);
113	5.54M	if (op == 0) { /* literal */
114	3.31M	Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?
115	3.31M	"inflate: literal '%c'\n" :
116	3.31M	"inflate: literal 0x%02x\n", here->val));
117	3.31M	*out++ = (unsigned char)(here->val);
118	3.31M	}
119	2.23M	else if (op & 16) { /* length base */
120	1.94M	len = (unsigned)(here->val);
121	1.94M	op &= 15; /* number of extra bits */
122	1.94M	if (op) {
123	600k	if (bits < op) {
124	809	hold += (unsigned long)(*in++) << bits;
125	809	bits += 8;
126	809	}
127	600k	len += (unsigned)hold & ((1U << op) - 1);
128	600k	hold >>= op;
129	600k	bits -= op;
130	600k	}
131	1.94M	Tracevv((stderr, "inflate: length %u\n", len));
132	1.94M	if (bits < 15) {
133	627k	hold += (unsigned long)(*in++) << bits;
134	627k	bits += 8;
135	627k	hold += (unsigned long)(*in++) << bits;
136	627k	bits += 8;
137	627k	}
138	1.94M	here = dcode + (hold & dmask);
139	1.98M	dodist:
140	1.98M	op = (unsigned)(here->bits);
141	1.98M	hold >>= op;
142	1.98M	bits -= op;
143	1.98M	op = (unsigned)(here->op);
144	1.98M	if (op & 16) { /* distance base */
145	1.94M	dist = (unsigned)(here->val);
146	1.94M	op &= 15; /* number of extra bits */
147	1.94M	if (bits < op) {
148	6.05k	hold += (unsigned long)(*in++) << bits;
149	6.05k	bits += 8;
150	6.05k	if (bits < op) {
151	194	hold += (unsigned long)(*in++) << bits;
152	194	bits += 8;
153	194	}
154	6.05k	}
155	1.94M	dist += (unsigned)hold & ((1U << op) - 1);
156		#ifdef INFLATE_STRICT
157		if (dist > dmax) {
158		strm->msg = (z_const char *)
159		"invalid distance too far back";
160		state->mode = BAD;
161		break;
162		}
163		#endif
164	1.94M	hold >>= op;
165	1.94M	bits -= op;
166	1.94M	Tracevv((stderr, "inflate: distance %u\n", dist));
167	1.94M	op = (unsigned)(out - beg); /* max distance in output */
168	1.94M	if (dist > op) { /* see if copy from window */
169	93.6k	op = dist - op; /* distance back in window */
170	93.6k	if (op > whave) {
171	798	if (state->sane) {
172	798	strm->msg = (z_const char *)
173	798	"invalid distance too far back";
174	798	state->mode = BAD;
175	798	break;
176	798	}
177		#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
178		if (len <= op - whave) {
179		do {
180		*out++ = 0;
181		} while (--len);
182		continue;
183		}
184		len -= op - whave;
185		do {
186		*out++ = 0;
187		} while (--op > whave);
188		if (op == 0) {
189		from = out - dist;
190		do {
191		out++ = from++;
192		} while (--len);
193		continue;
194		}
195		#endif
196	798	}
197	92.8k	from = window;
198	92.8k	if (wnext == 0) { /* very common case */
199	8.56k	from += wsize - op;
200	8.56k	if (op < len) { /* some from window */
201	320	len -= op;
202	31.0k	do {
203	31.0k	out++ = from++;
204	31.0k	} while (--op);
205	320	from = out - dist; /* rest from output */
206	320	}
207	8.56k	}
208	84.3k	else if (wnext < op) { /* wrap around window */
209	831	from += wsize + wnext - op;
210	831	op -= wnext;
211	831	if (op < len) { /* some from end of window */
212	87	len -= op;
213	1.32k	do {
214	1.32k	out++ = from++;
215	1.32k	} while (--op);
216	87	from = window;
217	87	if (wnext < len) { /* some from start of window */
218	30	op = wnext;
219	30	len -= op;
220	338	do {
221	338	out++ = from++;
222	338	} while (--op);
223	30	from = out - dist; /* rest from output */
224	30	}
225	87	}
226	831	}
227	83.4k	else { /* contiguous in window */
228	83.4k	from += wnext - op;
229	83.4k	if (op < len) { /* some from window */
230	8.65k	len -= op;
231	148k	do {
232	148k	out++ = from++;
233	148k	} while (--op);
234	8.65k	from = out - dist; /* rest from output */
235	8.65k	}
236	83.4k	}
237	672k	while (len > 2) {
238	579k	out++ = from++;
239	579k	out++ = from++;
240	579k	out++ = from++;
241	579k	len -= 3;
242	579k	}
243	92.8k	if (len) {
244	44.0k	out++ = from++;
245	44.0k	if (len > 1)
246	13.7k	out++ = from++;
247	44.0k	}
248	92.8k	}
249	1.85M	else {
250	1.85M	from = out - dist; /* copy direct from output */
251	28.2M	do { /* minimum length is three */
252	28.2M	out++ = from++;
253	28.2M	out++ = from++;
254	28.2M	out++ = from++;
255	28.2M	len -= 3;
256	28.2M	} while (len > 2);
257	1.85M	if (len) {
258	1.04M	out++ = from++;
259	1.04M	if (len > 1)
260	523k	out++ = from++;
261	1.04M	}
262	1.85M	}
263	1.94M	}
264	40.5k	else if ((op & 64) == 0) { /* 2nd level distance code */
265	40.5k	here = dcode + here->val + (hold & ((1U << op) - 1));
266	40.5k	goto dodist;
267	40.5k	}
268	27	else {
269	27	strm->msg = (z_const char *)"invalid distance code";
270	27	state->mode = BAD;
271	27	break;
272	27	}
273	1.98M	}
274	281k	else if ((op & 64) == 0) { /* 2nd level length code */
275	271k	here = lcode + here->val + (hold & ((1U << op) - 1));
276	271k	goto dolen;
277	271k	}
278	10.1k	else if (op & 32) { /* end-of-block */
279	10.1k	Tracevv((stderr, "inflate: end of block\n"));
280	10.1k	state->mode = TYPE;
281	10.1k	break;
282	10.1k	}
283	21	else {
284	21	strm->msg = (z_const char *)"invalid literal/length code";
285	21	state->mode = BAD;
286	21	break;
287	21	}
288	5.54M	} while (in < last && out < end);
289
290		/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
291	79.5k	len = bits >> 3;
292	79.5k	in -= len;
293	79.5k	bits -= len << 3;
294	79.5k	hold &= (1U << bits) - 1;
295
296		/* update state and return */
297	79.5k	strm->next_in = in;
298	79.5k	strm->next_out = out;
299	79.5k	strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
300	79.5k	strm->avail_out = (unsigned)(out < end ?
301	78.7k	257 + (end - out) : 257 - (out - end));
302	79.5k	state->hold = hold;
303	79.5k	state->bits = bits;
304	79.5k	return;
305	79.5k	}
306
307		/*
308		inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
309		- Using bit fields for code structure
310		- Different op definition to avoid & for extra bits (do & for table bits)
311		- Three separate decoding do-loops for direct, window, and wnext == 0
312		- Special case for distance > 1 copies to do overlapped load and store copy
313		- Explicit branch predictions (based on measured branch probabilities)
314		- Deferring match copy and interspersed it with decoding subsequent codes
315		- Swapping literal/length else
316		- Swapping window/direct else
317		- Larger unrolled copy loops (three is about right)
318		- Moving len -= 3 statement into middle of loop
319		*/
320
321		#endif /* !ASMINF */