delta_encoder.c revision 312518 
1///////////////////////////////////////////////////////////////////////////////
2//
3/// \file       delta_encoder.c
4/// \brief      Delta filter encoder
5//
6//  Author:     Lasse Collin
7//
8//  This file has been put into the public domain.
9//  You can do whatever you want with this file.
10//
11///////////////////////////////////////////////////////////////////////////////
12
13#include "delta_encoder.h"
14#include "delta_private.h"
15
16
17/// Copies and encodes the data at the same time. This is used when Delta
18/// is the first filter in the chain (and thus the last filter in the
19/// encoder's filter stack).
20static void
21copy_and_encode(lzma_delta_coder *coder,
22		const uint8_t *restrict in, uint8_t *restrict out, size_t size)
23{
24	const size_t distance = coder->distance;
25
26	for (size_t i = 0; i < size; ++i) {
27		const uint8_t tmp = coder->history[
28				(distance + coder->pos) & 0xFF];
29		coder->history[coder->pos-- & 0xFF] = in[i];
30		out[i] = in[i] - tmp;
31	}
32}
33
34
35/// Encodes the data in place. This is used when we are the last filter
36/// in the chain (and thus non-last filter in the encoder's filter stack).
37static void
38encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
39{
40	const size_t distance = coder->distance;
41
42	for (size_t i = 0; i < size; ++i) {
43		const uint8_t tmp = coder->history[
44				(distance + coder->pos) & 0xFF];
45		coder->history[coder->pos-- & 0xFF] = buffer[i];
46		buffer[i] -= tmp;
47	}
48}
49
50
51static lzma_ret
52delta_encode(void *coder_ptr, const lzma_allocator *allocator,
53		const uint8_t *restrict in, size_t *restrict in_pos,
54		size_t in_size, uint8_t *restrict out,
55		size_t *restrict out_pos, size_t out_size, lzma_action action)
56{
57	lzma_delta_coder *coder = coder_ptr;
58
59	lzma_ret ret;
60
61	if (coder->next.code == NULL) {
62		const size_t in_avail = in_size - *in_pos;
63		const size_t out_avail = out_size - *out_pos;
64		const size_t size = my_min(in_avail, out_avail);
65
66		copy_and_encode(coder, in + *in_pos, out + *out_pos, size);
67
68		*in_pos += size;
69		*out_pos += size;
70
71		ret = action != LZMA_RUN && *in_pos == in_size
72				? LZMA_STREAM_END : LZMA_OK;
73
74	} else {
75		const size_t out_start = *out_pos;
76
77		ret = coder->next.code(coder->next.coder, allocator,
78				in, in_pos, in_size, out, out_pos, out_size,
79				action);
80
81		encode_in_place(coder, out + out_start, *out_pos - out_start);
82	}
83
84	return ret;
85}
86
87
88static lzma_ret
89delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
90		const lzma_filter *filters_null lzma_attribute((__unused__)),
91		const lzma_filter *reversed_filters)
92{
93	lzma_delta_coder *coder = coder_ptr;
94
95	// Delta doesn't and will never support changing the options in
96	// the middle of encoding. If the app tries to change them, we
97	// simply ignore them.
98	return lzma_next_filter_update(
99			&coder->next, allocator, reversed_filters + 1);
100}
101
102
103extern lzma_ret
104lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
105		const lzma_filter_info *filters)
106{
107	next->code = &delta_encode;
108	next->update = &delta_encoder_update;
109	return lzma_delta_coder_init(next, allocator, filters);
110}
111
112
113extern lzma_ret
114lzma_delta_props_encode(const void *options, uint8_t *out)
115{
116	// The caller must have already validated the options, so it's
117	// LZMA_PROG_ERROR if they are invalid.
118	if (lzma_delta_coder_memusage(options) == UINT64_MAX)
119		return LZMA_PROG_ERROR;
120
121	const lzma_options_delta *opt = options;
122	out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
123
124	return LZMA_OK;
125}
126