1// SPDX-License-Identifier: 0BSD
2
3///////////////////////////////////////////////////////////////////////////////
4//
5/// \file       delta_encoder.c
6/// \brief      Delta filter encoder
7//
8//  Author:     Lasse Collin
9//
10///////////////////////////////////////////////////////////////////////////////
11
12#include "delta_encoder.h"
13#include "delta_private.h"
14
15
16/// Copies and encodes the data at the same time. This is used when Delta
17/// is the first filter in the chain (and thus the last filter in the
18/// encoder's filter stack).
19static void
20copy_and_encode(lzma_delta_coder *coder,
21		const uint8_t *restrict in, uint8_t *restrict out, size_t size)
22{
23	const size_t distance = coder->distance;
24
25	for (size_t i = 0; i < size; ++i) {
26		const uint8_t tmp = coder->history[
27				(distance + coder->pos) & 0xFF];
28		coder->history[coder->pos-- & 0xFF] = in[i];
29		out[i] = in[i] - tmp;
30	}
31}
32
33
34/// Encodes the data in place. This is used when we are the last filter
35/// in the chain (and thus non-last filter in the encoder's filter stack).
36static void
37encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
38{
39	const size_t distance = coder->distance;
40
41	for (size_t i = 0; i < size; ++i) {
42		const uint8_t tmp = coder->history[
43				(distance + coder->pos) & 0xFF];
44		coder->history[coder->pos-- & 0xFF] = buffer[i];
45		buffer[i] -= tmp;
46	}
47}
48
49
50static lzma_ret
51delta_encode(void *coder_ptr, const lzma_allocator *allocator,
52		const uint8_t *restrict in, size_t *restrict in_pos,
53		size_t in_size, uint8_t *restrict out,
54		size_t *restrict out_pos, size_t out_size, lzma_action action)
55{
56	lzma_delta_coder *coder = coder_ptr;
57
58	lzma_ret ret;
59
60	if (coder->next.code == NULL) {
61		const size_t in_avail = in_size - *in_pos;
62		const size_t out_avail = out_size - *out_pos;
63		const size_t size = my_min(in_avail, out_avail);
64
65		// in and out might be NULL. In such cases size == 0.
66		// Null pointer + 0 is undefined behavior so skip
67		// the call in that case as it would do nothing anyway.
68		if (size > 0)
69			copy_and_encode(coder, in + *in_pos, out + *out_pos,
70					size);
71
72		*in_pos += size;
73		*out_pos += size;
74
75		ret = action != LZMA_RUN && *in_pos == in_size
76				? LZMA_STREAM_END : LZMA_OK;
77
78	} else {
79		const size_t out_start = *out_pos;
80
81		ret = coder->next.code(coder->next.coder, allocator,
82				in, in_pos, in_size, out, out_pos, out_size,
83				action);
84
85		// Like above, avoid null pointer + 0.
86		const size_t size = *out_pos - out_start;
87		if (size > 0)
88			encode_in_place(coder, out + out_start, size);
89	}
90
91	return ret;
92}
93
94
95static lzma_ret
96delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
97		const lzma_filter *filters_null lzma_attribute((__unused__)),
98		const lzma_filter *reversed_filters)
99{
100	lzma_delta_coder *coder = coder_ptr;
101
102	// Delta doesn't and will never support changing the options in
103	// the middle of encoding. If the app tries to change them, we
104	// simply ignore them.
105	return lzma_next_filter_update(
106			&coder->next, allocator, reversed_filters + 1);
107}
108
109
110extern lzma_ret
111lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
112		const lzma_filter_info *filters)
113{
114	next->code = &delta_encode;
115	next->update = &delta_encoder_update;
116	return lzma_delta_coder_init(next, allocator, filters);
117}
118
119
120extern lzma_ret
121lzma_delta_props_encode(const void *options, uint8_t *out)
122{
123	// The caller must have already validated the options, so it's
124	// LZMA_PROG_ERROR if they are invalid.
125	if (lzma_delta_coder_memusage(options) == UINT64_MAX)
126		return LZMA_PROG_ERROR;
127
128	const lzma_options_delta *opt = options;
129	out[0] = opt->dist - LZMA_DELTA_DIST_MIN;
130
131	return LZMA_OK;
132}
133