Re: [devel] [PATCH] pack.c: downgrade XZ->LZMA automatically for small payloads

["Dmitry V. Levin" <ldv@altlinux.org>]

On Sun, Dec 20, 2020 at 01:43:47AM +0300, Alexey Tourbin wrote:
> Recent changes left downgradeLzmaLevel dysfunctional (because it does
> not recognize 'T').  In my view, the only advantage of XZ over LZMA is
> that XZ can can split input into blocks and compress them in parallel
> (resulting in a speed-up).  Other advantages, such as a checksum, are
> immaterial for our purpose (because the package manager must verify the
> integrity of a package beforehand).  Therefore, downgradeLzmaLevel will
> also downgrade XZ->LZMA automatically, for payloads smaller than
> 5*dictSize (the default blockSize being 3*dictSize, so that there are
> at least two blocks, the second block not too small).
> ---
>  build/pack.c | 54 ++++++++++++++++++++++++++++++++++++++++------------
>  1 file changed, 42 insertions(+), 12 deletions(-)
> 
> diff --git a/build/pack.c b/build/pack.c
> index 23ad89e72..a779e7918 100644
> --- a/build/pack.c
> +++ b/build/pack.c
> @@ -416,30 +416,60 @@ static uint64_t calcArchiveSize(TFI_t fi)
>  // which is 8-64M.  For smaller inputs, levels 7-9 are downgraded automatically.
>  static void downgradeLzmaLevel(char *mode, uint64_t archiveSize)
>  {
> -#define C(c) if (!(c)) return
> -    C(mode[1] == '7' || mode[1] == '8' || mode[1] == '9');
> -    C(mode[2] == '.');
> -    C(mode[3] == 'l' || mode[3] == 'x');
> -    C(mode[4] == 'z');
> +    if (!(mode[1] >= '0' && mode[1] <= '9'))
> +	return;
> +    char *p = &mode[2];
> +    if (*p == 'T') {
> +	do
> +	    p++;
> +	while (*p >= '0' && *p <= '9');
> +    }
> +    if (!(*p == '.' && (p[1] != 'l' || p[1] == 'x') && p[2] == 'z'))

Did you mean p[1] == 'l' here?


-- 
ldv