delta_encoder.c revision 292588 
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_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_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(lzma_coder *coder, 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_ret ret;
58
59	if (coder->next.code == NULL) {
60		const size_t in_avail = in_size - *in_pos;
61		const size_t out_avail = out_size - *out_pos;
62		const size_t size = my_min(in_avail, out_avail);
63
64		copy_and_encode(coder, in + *in_pos, out + *out_pos, size);
65
66		*in_pos += size;
67		*out_pos += size;
68
69		ret = action != LZMA_RUN && *in_pos == in_size
70				? LZMA_STREAM_END : LZMA_OK;
71
72	} else {
73		const size_t out_start = *out_pos;
74
75		ret = coder->next.code(coder->next.coder, allocator,
76				in, in_pos, in_size, out, out_pos, out_size,
77				action);
78
79		encode_in_place(coder, out + out_start, *out_pos - out_start);
80	}
81
82	return ret;
83}
84
85
86static lzma_ret
87delta_encoder_update(lzma_coder *coder, const lzma_allocator *allocator,
88		const lzma_filter *filters_null lzma_attribute((__unused__)),
89		const lzma_filter *reversed_filters)
90{
91	// Delta doesn't and will never support changing the options in
92	// the middle of encoding. If the app tries to change them, we
93	// simply ignore them.
94	return lzma_next_filter_update(
95			&coder->next, allocator, reversed_filters + 1);
96}
97
98
99extern lzma_ret
100lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
101		const lzma_filter_info *filters)
102{
103	next->code = &delta_encode;
104	next->update = &delta_encoder_update;
105	return lzma_delta_coder_init(next, allocator, filters);
106}
107
108
109extern lzma_ret
110lzma_delta_props_encode(const void *options, uint8_t *out)
111{
112	// The caller must have already validated the options, so it's
113	// LZMA_PROG_ERROR if they are invalid.
114	if (lzma_delta_coder_memusage(options) == UINT64_MAX)
115		return LZMA_PROG_ERROR;
116
117	const lzma_options_delta *opt = options;
118	out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
119
120	return LZMA_OK;
121}
122