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ircd::base: Optimize b64 table type; optimal lookup stride.

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This commit is contained in:
Jason Volk 2020-08-09 04:03:27 -07:00
parent abc41ca666
commit 3a887b4ca6
1 changed files with 33 additions and 14 deletions
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47
ircd/base.cc
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@ -97,8 +97,12 @@ namespace ircd::base
[[using gnu: visibility("internal"), aligned(64)]]
extern const u8
b64_encode_lut[64],
b64_encode_permute_tab[64];
b64_encode_permute_tab[64],
b64_encode_shift_ctrl[64];
[[using gnu: visibility("internal"), aligned(64)]]
extern const i32
b64_encode_lut[64];
static u8x64 b64encode(const u8x64 in) noexcept;
}
@ -120,6 +124,7 @@ ircd::base::b64_encode_lut
'4', '5', '6', '7', '8', '9', '+', '/',
};
/// For vpermb
/// From arXiv:1910.05109v1 [Mula, Lemire] 2 Oct 2019
decltype(ircd::base::b64_encode_permute_tab)
ircd::base::b64_encode_permute_tab
@ -142,6 +147,29 @@ ircd::base::b64_encode_permute_tab
45 + 1, 45 + 0, 45 + 2, 45 + 1,
};
/// For vpmultishiftqb
/// From arXiv:1910.05109v1 [Mula, Lemire] 2 Oct 2019
decltype(ircd::base::b64_encode_shift_ctrl)
ircd::base::b64_encode_shift_ctrl
{
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
};
/// Encoding in to base64 at out. Out must be 1.33+ larger than in
/// padding is not present in the returned view.
ircd::string_view
@ -236,12 +264,6 @@ ircd::u8x64
ircd::base::b64encode(const u8x64 in)
noexcept
{
static const int shift_ctrl[8]
{
(10 + 0), ( 4 + 0), (22 + 0), (16 + 0),
(10 + 32), ( 4 + 32), (22 + 32), (16 + 32),
};
size_t i, j, k;
// vpermb
@ -253,20 +275,17 @@ noexcept
u64x8 sh[8], perm(_perm);
for(i = 0; i < 8; ++i)
for(j = 0; j < 8; ++j)
sh[i][j] = perm[i] >> shift_ctrl[(i * 8 + j) % 8];
sh[i][j] = perm[i] >> b64_encode_shift_ctrl[i * 8 + j];
// TODO: not needed if vpmultishiftqb is emitted.
for(i = 0; i < 8; ++i)
for(j = 0; j < 8; ++j)
sh[i][j] &= 0x3f;
for(i = 0; i < 8; ++i)
for(j = 0; j < 8; ++j)
sh[i][j] = b64_encode_lut[sh[i][j]];
u8x64 ret;
for(i = 0, k = 0; i < 8; ++i)
for(j = 0; j < 8; ++j)
ret[k++] = sh[i][j];
ret[k++] = b64_encode_lut[sh[i][j]];
return ret;
}