// SPDX-License-Identifier: GPL-2.0

  /*
   * decompress.c
   *
   * Detect the decompression method based on magic number
   */
  
  #include <linux/decompress/generic.h>
  
  #include <linux/decompress/bunzip2.h>
  #include <linux/decompress/unlzma.h>

  #include <linux/decompress/unxz.h>

  #include <linux/decompress/inflate.h>

  #include <linux/decompress/unlzo.h>

  #include <linux/decompress/unlz4.h>

  #include <linux/decompress/unzstd.h>

  
  #include <linux/types.h>
  #include <linux/string.h>

  #include <linux/init.h>

  #include <linux/printk.h>

  #ifndef CONFIG_DECOMPRESS_GZIP
  # define gunzip NULL
  #endif
  #ifndef CONFIG_DECOMPRESS_BZIP2
  # define bunzip2 NULL
  #endif
  #ifndef CONFIG_DECOMPRESS_LZMA
  # define unlzma NULL
  #endif

  #ifndef CONFIG_DECOMPRESS_XZ
  # define unxz NULL
  #endif

  #ifndef CONFIG_DECOMPRESS_LZO
  # define unlzo NULL
  #endif

  #ifndef CONFIG_DECOMPRESS_LZ4
  # define unlz4 NULL
  #endif

  #ifndef CONFIG_DECOMPRESS_ZSTD
  # define unzstd NULL
  #endif

  struct compress_format {

  	unsigned char magic[2];
  	const char *name;
  	decompress_fn decompressor;

  };

  static const struct compress_format compressed_formats[] __initconst = {

  	{ {0x1f, 0x8b}, "gzip", gunzip },
  	{ {0x1f, 0x9e}, "gzip", gunzip },

  	{ {0x42, 0x5a}, "bzip2", bunzip2 },

  	{ {0x5d, 0x00}, "lzma", unlzma },

  	{ {0xfd, 0x37}, "xz", unxz },

  	{ {0x89, 0x4c}, "lzo", unlzo },

  	{ {0x02, 0x21}, "lz4", unlz4 },

  	{ {0x28, 0xb5}, "zstd", unzstd },

  	{ {0, 0}, NULL, NULL }
  };

  decompress_fn __init decompress_method(const unsigned char *inbuf, long len,

  				const char **name)
  {
  	const struct compress_format *cf;

  	if (len < 2) {
  		if (name)
  			*name = NULL;

  		return NULL;	/* Need at least this much... */

  	}

  	pr_debug("Compressed data magic: %#.2x %#.2x
  ", inbuf[0], inbuf[1]);

  	for (cf = compressed_formats; cf->name; cf++) {

  		if (!memcmp(inbuf, cf->magic, 2))
  			break;
  
  	}
  	if (name)
  		*name = cf->name;
  	return cf->decompressor;
  }