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lib/compression: Add helper function lzxpress_huffman_max_compressed_size()

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This allows the calculation of the worst case to be shared with callers.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
This commit is contained in:
Andrew Bartlett 2023-03-28 15:42:39 +13:00
parent 976dfc7585
commit 0ab5552c8c
2 changed files with 25 additions and 6 deletions
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23
lib/compression/lzxpress_huffman.c
View File

@ -1210,6 +1210,21 @@ static ssize_t lzx_huffman_compress_block(struct lzxhuff_compressor_context *cmp
return bytes_written;
}
/*
* lzxpress_huffman_max_compressed_size()
*
* Return the most bytes the compression can take, to allow
* pre-allocation.
*/
size_t lzxpress_huffman_max_compressed_size(size_t input_size)
{
/*
* In the worst case, the output size should be about the same as the
* input size, plus the 256 byte header per 64k block. We aim for
* ample, but within the order of magnitude.
*/
return input_size + (input_size / 8) + 270;
}
/*
* lzxpress_huffman_compress_talloc()
@ -1236,12 +1251,8 @@ ssize_t lzxpress_huffman_compress_talloc(TALLOC_CTX *mem_ctx,
uint8_t **output)
{
struct lzxhuff_compressor_mem *cmp = NULL;
/*
* In the worst case, the output size should be about the same as the
* input size, plus the 256 byte header per 64k block. We aim for
* ample, but within the order of magnitude.
*/
size_t alloc_size = input_size + (input_size / 8) + 270;
size_t alloc_size = lzxpress_huffman_max_compressed_size(input_size);
ssize_t output_size;
*output = talloc_array(mem_ctx, uint8_t, alloc_size);

8
lib/compression/lzxpress_huffman.h
View File

@ -83,5 +83,13 @@ uint8_t *lzxpress_huffman_decompress_talloc(TALLOC_CTX *mem_ctx,
size_t input_size,
size_t output_size);
/*
* lzxpress_huffman_max_compressed_size()
*
* Return the most bytes the compression can take, to allow
* pre-allocation.
*/
size_t lzxpress_huffman_max_compressed_size(size_t input_size);
#endif /* HAVE_LZXPRESS_HUFFMAN_H */