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ircd::utf: Complete the branchless UTF-8 decoder.

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This commit is contained in:
Jason Volk 2021-07-31 00:14:59 -07:00
parent 1eec9bfd64
commit f1e76604d0
1 changed files with 70 additions and 50 deletions
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120
ircd/utf.cc
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@ -302,82 +302,102 @@ noexcept
//
ircd::u32x16
ircd::utf8::decode(const u8x16 string)
ircd::utf8::decode(const u8x16 in)
noexcept
{
const u32x16 in
(
simd::lane_cast<u32x16, u8x16>(string)
);
const u32x16 is_single
const u8x16 is_single
(
(in & 0x80) == 0
);
const u32x16 is_lead
const u8x16 is_lead
(
(in - 0xc2) <= 0x32
);
const u32x16 is_trail
const u8x16 is_trail
(
in >= 0x80 && in < 0xbf
);
const u32x16 expect_trail
const u8x16 is_head
(
is_lead | is_single
);
const u8x16 len_mask[3]
{
(((in >= 0xe0) & 1) + ((in >= 0xf0) & 1) + 1) & is_lead
in >= 0xc0, in >= 0xe0, in >= 0xf0,
};
const u32x16 expect_length
const u8x16 expect_trail
(
1 + (len_mask[0] & 1) + (len_mask[1] & 1) + (len_mask[2] & 1)
);
const u8x16 len
(
(is_single & 1) | (is_lead & expect_trail)
);
const u8x16 head
(
in & is_head
);
const u8x16 lead[]
{
expect_trail + 1
0x3f & in & is_trail,
0xff & head & is_single,
0x1f & head & len_mask[0] & ~len_mask[1],
0x0f & head & len_mask[1] & ~len_mask[2],
0x07 & head & len_mask[2],
};
const u32x16 shift[4]
u8x16 full;
for(uint i(0); i < 16; ++i)
full[i] = lead[len[i]][i];
u8x16 shift {len & is_head};
shift |= (shl<0x20>(len) == 4) & 0;
shift |= (shl<0x20>(len) == 3) & 0;
shift |= (shl<0x20>(len) == 2) & 0;
shift |= (shl<0x20>(len) == 1) & 0;
shift |= (shl<0x18>(len) == 4) & 1;
shift |= (shl<0x18>(len) == 3) & 0;
shift |= (shl<0x18>(len) == 2) & 0;
shift |= (shl<0x18>(len) == 1) & 0;
shift |= (shl<0x10>(len) == 4) & 2;
shift |= (shl<0x10>(len) == 3) & 1;
shift |= (shl<0x10>(len) == 2) & 0;
shift |= (shl<0x10>(len) == 1) & 0;
shift |= (shl<0x08>(len) == 4) & 3;
shift |= (shl<0x08>(len) == 3) & 2;
shift |= (shl<0x08>(len) == 2) & 1;
shift |= (shl<0x08>(len) == 1) & 0;
shift -= 1U;
shift &= 0x03U;
shift *= 6U;
const u32x16 val
{
in << 0,
in << 8,
in << 16,
in << 24,
lane_cast<u32x16>(full) << lane_cast<u32x16>(shift)
};
const u32x16 multibyte_packs
{
in[0x00] | shift[0x01][0x01] | shift[0x02][0x02] | shift[0x03][0x03],
in[0x01] | shift[0x01][0x02] | shift[0x02][0x03] | shift[0x03][0x04],
in[0x02] | shift[0x01][0x03] | shift[0x02][0x04] | shift[0x03][0x05],
in[0x03] | shift[0x01][0x04] | shift[0x02][0x05] | shift[0x03][0x06],
in[0x04] | shift[0x01][0x05] | shift[0x02][0x06] | shift[0x03][0x07],
in[0x05] | shift[0x01][0x06] | shift[0x02][0x07] | shift[0x03][0x08],
in[0x06] | shift[0x01][0x07] | shift[0x02][0x08] | shift[0x03][0x09],
in[0x07] | shift[0x01][0x08] | shift[0x02][0x09] | shift[0x03][0x0a],
in[0x08] | shift[0x01][0x09] | shift[0x02][0x0a] | shift[0x03][0x0b],
in[0x09] | shift[0x01][0x0a] | shift[0x02][0x0b] | shift[0x03][0x0c],
in[0x0a] | shift[0x01][0x0b] | shift[0x02][0x0c] | shift[0x03][0x0d],
in[0x0b] | shift[0x01][0x0c] | shift[0x02][0x0d] | shift[0x03][0x0e],
in[0x0c] | shift[0x01][0x0d] | shift[0x02][0x0e] | shift[0x03][0x0f],
in[0x0d] | shift[0x01][0x0e] | shift[0x02][0x0f] | shift[0x03][0x0f],
in[0x0e] | shift[0x01][0x0f] | shift[0x02][0x0f] | shift[0x03][0x0f],
in[0x0f] | shift[0x01][0x0f] | shift[0x02][0x0f] | shift[0x03][0x0f],
};
const u8x16 incr
(
(shift == 0) & 1U
);
const u32x16 multibyte
{
0
| (multibyte_packs & (expect_length == 1) & 0x000000ffU)
| (multibyte_packs & (expect_length == 2) & 0x0000ffffU)
| (multibyte_packs & (expect_length == 3) & 0x00ffffffU)
| (multibyte_packs & (expect_length == 4) & 0xffffffffU)
};
u8x16 idx {0};
for(uint i(1); i < 16; ++i)
idx[i] = idx[i - 1] + incr[i - 1];
const u32x16 integers
{
(in & is_single) | (multibyte & is_lead)
};
u32x16 ret {0};
for(uint i(0); i < 16; ++i)
ret[idx[i]] |= val[i];
return integers;
return ret;
}
namespace ircd::utf8