/src/perfetto/buildtools/zlib/inffast.c

Source
/* inffast.c -- fast decoding
 * Copyright (C) 1995-2017 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 >= INFLATE_FAST_MIN_INPUT (6 bytes)
        strm->avail_out >= INFLATE_FAST_MIN_OUTPUT (258 bytes)
        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:

    INFLATE_FAST_MIN_INPUT: 6 bytes

    - 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.

    INFLATE_FAST_MIN_OUTPUT: 258 bytes

    - 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
      available output space while decoding.
 */
void ZLIB_INTERNAL inflate_fast(strm, start)
z_streamp strm;
unsigned start;         /* inflate()'s starting value for strm->avail_out */
{
    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 - (INFLATE_FAST_MIN_INPUT - 1));
    out = strm->next_out;
    beg = out - (start - strm->avail_out);
    end = out + (strm->avail_out - (INFLATE_FAST_MIN_OUTPUT - 1));
#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 = (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 =
                                (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 = (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 = (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 ?
        (INFLATE_FAST_MIN_INPUT - 1) + (last - in) :
        (INFLATE_FAST_MIN_INPUT - 1) - (in - last));
    strm->avail_out = (unsigned)(out < end ?
        (INFLATE_FAST_MIN_OUTPUT - 1) + (end - out) :
        (INFLATE_FAST_MIN_OUTPUT - 1) - (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: 2026-02-14 06:29

Line	Count	Source
1		/* inffast.c -- fast decoding
2		* Copyright (C) 1995-2017 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 >= INFLATE_FAST_MIN_INPUT (6 bytes)
27		strm->avail_out >= INFLATE_FAST_MIN_OUTPUT (258 bytes)
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		INFLATE_FAST_MIN_INPUT: 6 bytes
40
41		- The maximum input bits used by a length/distance pair is 15 bits for the
42		length code, 5 bits for the length extra, 15 bits for the distance code,
43		and 13 bits for the distance extra. This totals 48 bits, or six bytes.
44		Therefore if strm->avail_in >= 6, then there is enough input to avoid
45		checking for available input while decoding.
46
47		INFLATE_FAST_MIN_OUTPUT: 258 bytes
48
49		- The maximum bytes that a single length/distance pair can output is 258
50		bytes, which is the maximum length that can be coded. inflate_fast()
51		requires strm->avail_out >= 258 for each loop to avoid checking for
52		available output space while decoding.
53		*/
54		void ZLIB_INTERNAL inflate_fast(strm, start)
55		z_streamp strm;
56		unsigned start; /* inflate()'s starting value for strm->avail_out */
57	183	{
58	183	struct inflate_state FAR *state;
59	183	z_const unsigned char FAR in; / local strm->next_in */
60	183	z_const unsigned char FAR last; / have enough input while in < last */
61	183	unsigned char FAR out; / local strm->next_out */
62	183	unsigned char FAR beg; / inflate()'s initial strm->next_out */
63	183	unsigned char FAR end; / while out < end, enough space available */
64		#ifdef INFLATE_STRICT
65		unsigned dmax; /* maximum distance from zlib header */
66		#endif
67	183	unsigned wsize; /* window size or zero if not using window */
68	183	unsigned whave; /* valid bytes in the window */
69	183	unsigned wnext; /* window write index */
70	183	unsigned char FAR window; / allocated sliding window, if wsize != 0 */
71	183	unsigned long hold; /* local strm->hold */
72	183	unsigned bits; /* local strm->bits */
73	183	code const FAR lcode; / local strm->lencode */
74	183	code const FAR dcode; / local strm->distcode */
75	183	unsigned lmask; /* mask for first level of length codes */
76	183	unsigned dmask; /* mask for first level of distance codes */
77	183	code const here; / retrieved table entry */
78	183	unsigned op; /* code bits, operation, extra bits, or */
79		/* window position, window bytes to copy */
80	183	unsigned len; /* match length, unused bytes */
81	183	unsigned dist; /* match distance */
82	183	unsigned char FAR from; / where to copy match from */
83
84		/* copy state to local variables */
85	183	state = (struct inflate_state FAR *)strm->state;
86	183	in = strm->next_in;
87	183	last = in + (strm->avail_in - (INFLATE_FAST_MIN_INPUT - 1));
88	183	out = strm->next_out;
89	183	beg = out - (start - strm->avail_out);
90	183	end = out + (strm->avail_out - (INFLATE_FAST_MIN_OUTPUT - 1));
91		#ifdef INFLATE_STRICT
92		dmax = state->dmax;
93		#endif
94	183	wsize = state->wsize;
95	183	whave = state->whave;
96	183	wnext = state->wnext;
97	183	window = state->window;
98	183	hold = state->hold;
99	183	bits = state->bits;
100	183	lcode = state->lencode;
101	183	dcode = state->distcode;
102	183	lmask = (1U << state->lenbits) - 1;
103	183	dmask = (1U << state->distbits) - 1;
104
105		/* decode literals and length/distances until end-of-block or not enough
106		input data or output space */
107	366	do {
108	366	if (bits < 15) {
109	366	hold += (unsigned long)(*in++) << bits;
110	366	bits += 8;
111	366	hold += (unsigned long)(*in++) << bits;
112	366	bits += 8;
113	366	}
114	366	here = lcode + (hold & lmask);
115	366	dolen:
116	366	op = (unsigned)(here->bits);
117	366	hold >>= op;
118	366	bits -= op;
119	366	op = (unsigned)(here->op);
120	366	if (op == 0) { /* literal */
121	183	Tracevv((stderr, here->val >= 0x20 && here->val < 0x7f ?
122	183	"inflate: literal '%c'\n" :
123	183	"inflate: literal 0x%02x\n", here->val));
124	183	*out++ = (unsigned char)(here->val);
125	183	}
126	183	else if (op & 16) { /* length base */
127	0	len = (unsigned)(here->val);
128	0	op &= 15; /* number of extra bits */
129	0	if (op) {
130	0	if (bits < op) {
131	0	hold += (unsigned long)(*in++) << bits;
132	0	bits += 8;
133	0	}
134	0	len += (unsigned)hold & ((1U << op) - 1);
135	0	hold >>= op;
136	0	bits -= op;
137	0	}
138	0	Tracevv((stderr, "inflate: length %u\n", len));
139	0	if (bits < 15) {
140	0	hold += (unsigned long)(*in++) << bits;
141	0	bits += 8;
142	0	hold += (unsigned long)(*in++) << bits;
143	0	bits += 8;
144	0	}
145	0	here = dcode + (hold & dmask);
146	0	dodist:
147	0	op = (unsigned)(here->bits);
148	0	hold >>= op;
149	0	bits -= op;
150	0	op = (unsigned)(here->op);
151	0	if (op & 16) { /* distance base */
152	0	dist = (unsigned)(here->val);
153	0	op &= 15; /* number of extra bits */
154	0	if (bits < op) {
155	0	hold += (unsigned long)(*in++) << bits;
156	0	bits += 8;
157	0	if (bits < op) {
158	0	hold += (unsigned long)(*in++) << bits;
159	0	bits += 8;
160	0	}
161	0	}
162	0	dist += (unsigned)hold & ((1U << op) - 1);
163		#ifdef INFLATE_STRICT
164		if (dist > dmax) {
165		strm->msg = (char *)"invalid distance too far back";
166		state->mode = BAD;
167		break;
168		}
169		#endif
170	0	hold >>= op;
171	0	bits -= op;
172	0	Tracevv((stderr, "inflate: distance %u\n", dist));
173	0	op = (unsigned)(out - beg); /* max distance in output */
174	0	if (dist > op) { /* see if copy from window */
175	0	op = dist - op; /* distance back in window */
176	0	if (op > whave) {
177	0	if (state->sane) {
178	0	strm->msg =
179	0	(char *)"invalid distance too far back";
180	0	state->mode = BAD;
181	0	break;
182	0	}
183		#ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
184		if (len <= op - whave) {
185		do {
186		*out++ = 0;
187		} while (--len);
188		continue;
189		}
190		len -= op - whave;
191		do {
192		*out++ = 0;
193		} while (--op > whave);
194		if (op == 0) {
195		from = out - dist;
196		do {
197		out++ = from++;
198		} while (--len);
199		continue;
200		}
201		#endif
202	0	}
203	0	from = window;
204	0	if (wnext == 0) { /* very common case */
205	0	from += wsize - op;
206	0	if (op < len) { /* some from window */
207	0	len -= op;
208	0	do {
209	0	out++ = from++;
210	0	} while (--op);
211	0	from = out - dist; /* rest from output */
212	0	}
213	0	}
214	0	else if (wnext < op) { /* wrap around window */
215	0	from += wsize + wnext - op;
216	0	op -= wnext;
217	0	if (op < len) { /* some from end of window */
218	0	len -= op;
219	0	do {
220	0	out++ = from++;
221	0	} while (--op);
222	0	from = window;
223	0	if (wnext < len) { /* some from start of window */
224	0	op = wnext;
225	0	len -= op;
226	0	do {
227	0	out++ = from++;
228	0	} while (--op);
229	0	from = out - dist; /* rest from output */
230	0	}
231	0	}
232	0	}
233	0	else { /* contiguous in window */
234	0	from += wnext - op;
235	0	if (op < len) { /* some from window */
236	0	len -= op;
237	0	do {
238	0	out++ = from++;
239	0	} while (--op);
240	0	from = out - dist; /* rest from output */
241	0	}
242	0	}
243	0	while (len > 2) {
244	0	out++ = from++;
245	0	out++ = from++;
246	0	out++ = from++;
247	0	len -= 3;
248	0	}
249	0	if (len) {
250	0	out++ = from++;
251	0	if (len > 1)
252	0	out++ = from++;
253	0	}
254	0	}
255	0	else {
256	0	from = out - dist; /* copy direct from output */
257	0	do { /* minimum length is three */
258	0	out++ = from++;
259	0	out++ = from++;
260	0	out++ = from++;
261	0	len -= 3;
262	0	} while (len > 2);
263	0	if (len) {
264	0	out++ = from++;
265	0	if (len > 1)
266	0	out++ = from++;
267	0	}
268	0	}
269	0	}
270	0	else if ((op & 64) == 0) { /* 2nd level distance code */
271	0	here = dcode + here->val + (hold & ((1U << op) - 1));
272	0	goto dodist;
273	0	}
274	0	else {
275	0	strm->msg = (char *)"invalid distance code";
276	0	state->mode = BAD;
277	0	break;
278	0	}
279	0	}
280	183	else if ((op & 64) == 0) { /* 2nd level length code */
281	0	here = lcode + here->val + (hold & ((1U << op) - 1));
282	0	goto dolen;
283	0	}
284	183	else if (op & 32) { /* end-of-block */
285	183	Tracevv((stderr, "inflate: end of block\n"));
286	183	state->mode = TYPE;
287	183	break;
288	183	}
289	0	else {
290	0	strm->msg = (char *)"invalid literal/length code";
291	0	state->mode = BAD;
292	0	break;
293	0	}
294	366	} while (in < last && out < end);
295
296		/* return unused bytes (on entry, bits < 8, so in won't go too far back) */
297	183	len = bits >> 3;
298	183	in -= len;
299	183	bits -= len << 3;
300	183	hold &= (1U << bits) - 1;
301
302		/* update state and return */
303	183	strm->next_in = in;
304	183	strm->next_out = out;
305	183	strm->avail_in = (unsigned)(in < last ?
306	183	(INFLATE_FAST_MIN_INPUT - 1) + (last - in) :
307	183	(INFLATE_FAST_MIN_INPUT - 1) - (in - last));
308	183	strm->avail_out = (unsigned)(out < end ?
309	183	(INFLATE_FAST_MIN_OUTPUT - 1) + (end - out) :
310	183	(INFLATE_FAST_MIN_OUTPUT - 1) - (out - end));
311	183	state->hold = hold;
312	183	state->bits = bits;
313	183	return;
314	183	}
315
316		/*
317		inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
318		- Using bit fields for code structure
319		- Different op definition to avoid & for extra bits (do & for table bits)
320		- Three separate decoding do-loops for direct, window, and wnext == 0
321		- Special case for distance > 1 copies to do overlapped load and store copy
322		- Explicit branch predictions (based on measured branch probabilities)
323		- Deferring match copy and interspersed it with decoding subsequent codes
324		- Swapping literal/length else
325		- Swapping window/direct else
326		- Larger unrolled copy loops (three is about right)
327		- Moving len -= 3 statement into middle of loop
328		*/
329
330		#endif /* !ASMINF */