On Sun, 2023-09-24 at 00:05 +0100, Joern Rennecke wrote:
>
> Although maybe Oleg Endo's library, as mentioned in
> https://gcc.gnu.org/pipermail/gcc-patches/2022-March/591748.html ,
> might be suitable? What is the license for that?
>
>
I haven't published the library, but I think I could do that.
It's a C++-14 header-only thing and uses templates + constexpr to generate
the .rodata lookup tables. It's convenient for an application project, as
it doesn't require any generator tool in the build. This might be not a big
advantage in the context of GCC.
Since the tables are computed during compile-time, there is no particular
optimization implemented. The run-time function is also nothing fancy:
static constexpr uint8_t table_index (value_type rem, uint8_t x)
{
if (ReflectInput)
return x ^ rem;
else
return x ^ (BitCount > 8 ? (rem >> (BitCount - 8))
: (rem << (8 - BitCount)));
}
static constexpr value_type shift (value_type rem)
{
return ReflectInput ? rem >> 8 : rem << 8;
}
static value_type
default_process_bytes (value_type rem, const uint8_t* in, const uint8_t* in_end)
{
for (; in != in_end; ++in)
{
auto i = table_index (rem, *in);
rem = table[i] ^ shift (rem);
}
return rem;
}
Anyway, let me know if anyone is interested.
Cheers,
Oleg
