liblzma: Fix a typo in a comment

[xz/debian.git] / src / liblzma / simple / simple_coder.c

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       simple_coder.c
/// \brief      Wrapper for simple filters
///
/// Simple filters don't change the size of the data i.e. number of bytes
/// in equals the number of bytes out.
//
//  Author:     Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////

#include "simple_private.h"


/// Copied or encodes/decodes more data to out[].
static lzma_ret
copy_or_code(lzma_simple_coder *coder, 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)
{
        assert(!coder->end_was_reached);

        if (coder->next.code == NULL) {
                lzma_bufcpy(in, in_pos, in_size, out, out_pos, out_size);

                // Check if end of stream was reached.
                if (coder->is_encoder && action == LZMA_FINISH
                                && *in_pos == in_size)
                        coder->end_was_reached = true;

        } else {
                // Call the next coder in the chain to provide us some data.
                const lzma_ret ret = coder->next.code(
                                coder->next.coder, allocator,
                                in, in_pos, in_size,
                                out, out_pos, out_size, action);

                if (ret == LZMA_STREAM_END) {
                        assert(!coder->is_encoder
                                        || action == LZMA_FINISH);
                        coder->end_was_reached = true;

                } else if (ret != LZMA_OK) {
                        return ret;
                }
        }

        return LZMA_OK;
}


static size_t
call_filter(lzma_simple_coder *coder, uint8_t *buffer, size_t size)
{
        const size_t filtered = coder->filter(coder->simple,
                        coder->now_pos, coder->is_encoder,
                        buffer, size);
        coder->now_pos += filtered;
        return filtered;
}


static lzma_ret
simple_code(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_simple_coder *coder = coder_ptr;

        // TODO: Add partial support for LZMA_SYNC_FLUSH. We can support it
        // in cases when the filter is able to filter everything. With most
        // simple filters it can be done at offset that is a multiple of 2,
        // 4, or 16. With x86 filter, it needs good luck, and thus cannot
        // be made to work predictably.
        if (action == LZMA_SYNC_FLUSH)
                return LZMA_OPTIONS_ERROR;

        // Flush already filtered data from coder->buffer[] to out[].
        if (coder->pos < coder->filtered) {
                lzma_bufcpy(coder->buffer, &coder->pos, coder->filtered,
                                out, out_pos, out_size);

                // If we couldn't flush all the filtered data, return to
                // application immediately.
                if (coder->pos < coder->filtered)
                        return LZMA_OK;

                if (coder->end_was_reached) {
                        assert(coder->filtered == coder->size);
                        return LZMA_STREAM_END;
                }
        }

        // If we get here, there is no filtered data left in the buffer.
        coder->filtered = 0;

        assert(!coder->end_was_reached);

        // If there is more output space left than there is unfiltered data
        // in coder->buffer[], flush coder->buffer[] to out[], and copy/code
        // more data to out[] hopefully filling it completely. Then filter
        // the data in out[]. This step is where most of the data gets
        // filtered if the buffer sizes used by the application are reasonable.
        const size_t out_avail = out_size - *out_pos;
        const size_t buf_avail = coder->size - coder->pos;
        if (out_avail > buf_avail || buf_avail == 0) {
                // Store the old position so that we know from which byte
                // to start filtering.
                const size_t out_start = *out_pos;

                // Flush data from coder->buffer[] to out[], but don't reset
                // coder->pos and coder->size yet. This way the coder can be
                // restarted if the next filter in the chain returns e.g.
                // LZMA_MEM_ERROR.
                //
                // Do the memcpy() conditionally because out can be NULL
                // (in which case buf_avail is always 0). Calling memcpy()
                // with a null-pointer is undefined even if the third
                // argument is 0.
                if (buf_avail > 0)
                        memcpy(out + *out_pos, coder->buffer + coder->pos,
                                        buf_avail);

                *out_pos += buf_avail;

                // Copy/Encode/Decode more data to out[].
                {
                        const lzma_ret ret = copy_or_code(coder, allocator,
                                        in, in_pos, in_size,
                                        out, out_pos, out_size, action);
                        assert(ret != LZMA_STREAM_END);
                        if (ret != LZMA_OK)
                                return ret;
                }

                // Filter out[] unless there is nothing to filter.
                // This way we avoid null pointer + 0 (undefined behavior)
                // when out == NULL.
                const size_t size = *out_pos - out_start;
                const size_t filtered = size == 0 ? 0 : call_filter(
                                coder, out + out_start, size);

                const size_t unfiltered = size - filtered;
                assert(unfiltered <= coder->allocated / 2);

                // Now we can update coder->pos and coder->size, because
                // the next coder in the chain (if any) was successful.
                coder->pos = 0;
                coder->size = unfiltered;

                if (coder->end_was_reached) {
                        // The last byte has been copied to out[] already.
                        // They are left as is.
                        coder->size = 0;

                } else if (unfiltered > 0) {
                        // There is unfiltered data left in out[]. Copy it to
                        // coder->buffer[] and rewind *out_pos appropriately.
                        *out_pos -= unfiltered;
                        memcpy(coder->buffer, out + *out_pos, unfiltered);
                }
        } else if (coder->pos > 0) {
                memmove(coder->buffer, coder->buffer + coder->pos, buf_avail);
                coder->size -= coder->pos;
                coder->pos = 0;
        }

        assert(coder->pos == 0);

        // If coder->buffer[] isn't empty, try to fill it by copying/decoding
        // more data. Then filter coder->buffer[] and copy the successfully
        // filtered data to out[]. It is probable, that some filtered and
        // unfiltered data will be left to coder->buffer[].
        if (coder->size > 0) {
                {
                        const lzma_ret ret = copy_or_code(coder, allocator,
                                        in, in_pos, in_size,
                                        coder->buffer, &coder->size,
                                        coder->allocated, action);
                        assert(ret != LZMA_STREAM_END);
                        if (ret != LZMA_OK)
                                return ret;
                }

                coder->filtered = call_filter(
                                coder, coder->buffer, coder->size);

                // Everything is considered to be filtered if coder->buffer[]
                // contains the last bytes of the data.
                if (coder->end_was_reached)
                        coder->filtered = coder->size;

                // Flush as much as possible.
                lzma_bufcpy(coder->buffer, &coder->pos, coder->filtered,
                                out, out_pos, out_size);
        }

        // Check if we got everything done.
        if (coder->end_was_reached && coder->pos == coder->size)
                return LZMA_STREAM_END;

        return LZMA_OK;
}


static void
simple_coder_end(void *coder_ptr, const lzma_allocator *allocator)
{
        lzma_simple_coder *coder = coder_ptr;
        lzma_next_end(&coder->next, allocator);
        lzma_free(coder->simple, allocator);
        lzma_free(coder, allocator);
        return;
}


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

        // No update support, just call the next filter in the chain.
        return lzma_next_filter_update(
                        &coder->next, allocator, reversed_filters + 1);
}


extern lzma_ret
lzma_simple_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,
                const lzma_filter_info *filters,
                size_t (*filter)(void *simple, uint32_t now_pos,
                        bool is_encoder, uint8_t *buffer, size_t size),
                size_t simple_size, size_t unfiltered_max,
                uint32_t alignment, bool is_encoder)
{
        // Allocate memory for the lzma_simple_coder structure if needed.
        lzma_simple_coder *coder = next->coder;
        if (coder == NULL) {
                // Here we allocate space also for the temporary buffer. We
                // need twice the size of unfiltered_max, because then it
                // is always possible to filter at least unfiltered_max bytes
                // more data in coder->buffer[] if it can be filled completely.
                coder = lzma_alloc(sizeof(lzma_simple_coder)
                                + 2 * unfiltered_max, allocator);
                if (coder == NULL)
                        return LZMA_MEM_ERROR;

                next->coder = coder;
                next->code = &simple_code;
                next->end = &simple_coder_end;
                next->update = &simple_coder_update;

                coder->next = LZMA_NEXT_CODER_INIT;
                coder->filter = filter;
                coder->allocated = 2 * unfiltered_max;

                // Allocate memory for filter-specific data structure.
                if (simple_size > 0) {
                        coder->simple = lzma_alloc(simple_size, allocator);
                        if (coder->simple == NULL)
                                return LZMA_MEM_ERROR;
                } else {
                        coder->simple = NULL;
                }
        }

        if (filters[0].options != NULL) {
                const lzma_options_bcj *simple = filters[0].options;
                coder->now_pos = simple->start_offset;
                if (coder->now_pos & (alignment - 1))
                        return LZMA_OPTIONS_ERROR;
        } else {
                coder->now_pos = 0;
        }

        // Reset variables.
        coder->is_encoder = is_encoder;
        coder->end_was_reached = false;
        coder->pos = 0;
        coder->filtered = 0;
        coder->size = 0;

        return lzma_next_filter_init(&coder->next, allocator, filters + 1);
}