source: vbox/trunk/src/libs/liblzma-5.8.1/delta/delta_encoder.c

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       delta_encoder.c
/// \brief      Delta filter encoder
//
//  Author:     Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#include "delta_encoder.h"
#include "delta_private.h"


/// Copies and encodes the data at the same time. This is used when Delta
/// is the first filter in the chain (and thus the last filter in the
/// encoder's filter stack).
static void
copy_and_encode(lzma_delta_coder *coder,
                const uint8_t *restrict in, uint8_t *restrict out, size_t size)
{
        const size_t distance = coder->distance;

        for (size_t i = 0; i < size; ++i) {
                const uint8_t tmp = coder->history[
                                (distance + coder->pos) & 0xFF];
                coder->history[coder->pos-- & 0xFF] = in[i];
                out[i] = in[i] - tmp;
        }
}


/// Encodes the data in place. This is used when we are the last filter
/// in the chain (and thus non-last filter in the encoder's filter stack).
static void
encode_in_place(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
{
        const size_t distance = coder->distance;

        for (size_t i = 0; i < size; ++i) {
                const uint8_t tmp = coder->history[
                                (distance + coder->pos) & 0xFF];
                coder->history[coder->pos-- & 0xFF] = buffer[i];
                buffer[i] -= tmp;
        }
}


static lzma_ret
delta_encode(void *coder_ptr, const lzma_allocator *allocator,
                const uint8_t *restrict in, size_t *restrict in_pos,
                size_t in_size, uint8_t *restrict out,
                size_t *restrict out_pos, size_t out_size, lzma_action action)
{
        lzma_delta_coder *coder = coder_ptr;

        lzma_ret ret;

        if (coder->next.code == NULL) {
                const size_t in_avail = in_size - *in_pos;
                const size_t out_avail = out_size - *out_pos;
                const size_t size = my_min(in_avail, out_avail);

                // in and out might be NULL. In such cases size == 0.
                // Null pointer + 0 is undefined behavior so skip
                // the call in that case as it would do nothing anyway.
                if (size > 0)
                        copy_and_encode(coder, in + *in_pos, out + *out_pos,
                                        size);

                *in_pos += size;
                *out_pos += size;

                ret = action != LZMA_RUN && *in_pos == in_size
                                ? LZMA_STREAM_END : LZMA_OK;

        } else {
                const size_t out_start = *out_pos;

                ret = coder->next.code(coder->next.coder, allocator,
                                in, in_pos, in_size, out, out_pos, out_size,
                                action);

                // Like above, avoid null pointer + 0.
                const size_t size = *out_pos - out_start;
                if (size > 0)
                        encode_in_place(coder, out + out_start, size);
        }

        return ret;
}


static lzma_ret
delta_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
                const lzma_filter *filters_null lzma_attribute((__unused__)),
                const lzma_filter *reversed_filters)
{
        lzma_delta_coder *coder = coder_ptr;

        // Delta doesn't and will never support changing the options in
        // the middle of encoding. If the app tries to change them, we
        // simply ignore them.
        return lzma_next_filter_update(
                        &coder->next, allocator, reversed_filters + 1);
}


extern lzma_ret
lzma_delta_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
                const lzma_filter_info *filters)
{
        next->code = &delta_encode;
        next->update = &delta_encoder_update;
        return lzma_delta_coder_init(next, allocator, filters);
}


extern lzma_ret
lzma_delta_props_encode(const void *options, uint8_t *out)
{
        // The caller must have already validated the options, so it's
        // LZMA_PROG_ERROR if they are invalid.
        if (lzma_delta_coder_memusage(options) == UINT64_MAX)
                return LZMA_PROG_ERROR;

        const lzma_options_delta *opt = options;
        out[0] = opt->dist - LZMA_DELTA_DIST_MIN;

        return LZMA_OK;
}