// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * xpress_decompress.c - A decompressor for the XPRESS compression format
 * (Huffman variant), which can be used in "System Compressed" files.  This is
 * based on the code from wimlib.
 *
 * Copyright (C) 2015 Eric Biggers
 */

#include "decompress_common.h"
#include "lib.h"

#define XPRESS_NUM_SYMBOLS      512
#define XPRESS_MAX_CODEWORD_LEN 15
#define XPRESS_MIN_MATCH_LEN    3

/* This value is chosen for fast decompression.  */
#define XPRESS_TABLEBITS 12

/* Reusable heap-allocated memory for XPRESS decompression  */
struct xpress_decompressor {

        /* The Huffman decoding table  */
        u16 decode_table[(1 << XPRESS_TABLEBITS) + 2 * XPRESS_NUM_SYMBOLS];

        /* An array that maps symbols to codeword lengths  */
        u8 lens[XPRESS_NUM_SYMBOLS];

        /* Temporary space for make_huffman_decode_table()  */
        u16 working_space[2 * (1 + XPRESS_MAX_CODEWORD_LEN) +
                          XPRESS_NUM_SYMBOLS];
};

/*
 * xpress_allocate_decompressor - Allocate an XPRESS decompressor
 *
 * Return the pointer to the decompressor on success, or return NULL and set
 * errno on failure.
 */
struct xpress_decompressor *xpress_allocate_decompressor(void)
{
        return kmalloc_obj(struct xpress_decompressor, GFP_NOFS);
}

/*
 * xpress_decompress - Decompress a buffer of XPRESS-compressed data
 *
 * @decompressor:       A decompressor that was allocated with
 *                      xpress_allocate_decompressor()
 * @compressed_data:    The buffer of data to decompress
 * @compressed_size:    Number of bytes of compressed data
 * @uncompressed_data:  The buffer in which to store the decompressed data
 * @uncompressed_size:  The number of bytes the data decompresses into
 *
 * Return 0 on success, or return -1 and set errno on failure.
 */
int xpress_decompress(struct xpress_decompressor *decompressor,
                      const void *compressed_data, size_t compressed_size,
                      void *uncompressed_data, size_t uncompressed_size)
{
        struct xpress_decompressor *d = decompressor;
        const u8 * const in_begin = compressed_data;
        u8 * const out_begin = uncompressed_data;
        u8 *out_next = out_begin;
        u8 * const out_end = out_begin + uncompressed_size;
        struct input_bitstream is;
        u32 i;

        /* Read the Huffman codeword lengths.  */
        if (compressed_size < XPRESS_NUM_SYMBOLS / 2)
                goto invalid;
        for (i = 0; i < XPRESS_NUM_SYMBOLS / 2; i++) {
                d->lens[i*2 + 0] = in_begin[i] & 0xF;
                d->lens[i*2 + 1] = in_begin[i] >> 4;
        }

        /* Build a decoding table for the Huffman code.  */
        if (make_huffman_decode_table(d->decode_table, XPRESS_NUM_SYMBOLS,
                                      XPRESS_TABLEBITS, d->lens,
                                      XPRESS_MAX_CODEWORD_LEN,
                                      d->working_space))
                goto invalid;

        /* Decode the matches and literals.  */

        init_input_bitstream(&is, in_begin + XPRESS_NUM_SYMBOLS / 2,
                             compressed_size - XPRESS_NUM_SYMBOLS / 2);

        while (out_next != out_end) {
                u32 sym;
                u32 log2_offset;
                u32 length;
                u32 offset;

                sym = read_huffsym(&is, d->decode_table,
                                   XPRESS_TABLEBITS, XPRESS_MAX_CODEWORD_LEN);
                if (sym < 256) {
                        /* Literal  */
                        *out_next++ = sym;
                } else {
                        /* Match  */
                        length = sym & 0xf;
                        log2_offset = (sym >> 4) & 0xf;

                        bitstream_ensure_bits(&is, 16);

                        offset = ((u32)1 << log2_offset) |
                                 bitstream_pop_bits(&is, log2_offset);

                        if (length == 0xf) {
                                length += bitstream_read_byte(&is);
                                if (length == 0xf + 0xff)
                                        length = bitstream_read_u16(&is);
                        }
                        length += XPRESS_MIN_MATCH_LEN;

                        if (offset > (size_t)(out_next - out_begin))
                                goto invalid;

                        if (length > (size_t)(out_end - out_next))
                                goto invalid;

                        out_next = lz_copy(out_next, length, offset, out_end,
                                           XPRESS_MIN_MATCH_LEN);
                }
        }
        return 0;

invalid:
        return -1;
}

/*
 * xpress_free_decompressor - Free an XPRESS decompressor
 *
 * @decompressor:       A decompressor that was allocated with
 *                      xpress_allocate_decompressor(), or NULL.
 */
void xpress_free_decompressor(struct xpress_decompressor *decompressor)
{
        kfree(decompressor);
}