Whitespace character filtering #33

mayeut · 2016-11-06T15:50:29Z

This is a new issue to discuss whitespace character filtering as mentioned in #15 and #27

The implementation will probably depend on density of whitespace characters.

few occurrences, not grouped together (e.g. one new line every 80 characters): update error handling to filter those characters (easy, fast, tested on my end).
few occurrences of group of whitespace (e.g. one new line + n spaces every 80 characters): update error handling to filter those characters by skipping multiple characters at a time (not tested at all on my end).
many occurrences: a preprocess step might be more suited. This is still quite slow (1st implementation was based on code snippet from Decoding from uint16_t[] #15, changed that with a LUT for the shuffle mask):
SSE4.2 implementation

while (srclen >= 32U) {
	// Characters to be checked (all should be valid, repeat the first ones):
	const __m128i whitespaces = _mm_setr_epi8(
		'\n','\r','\t', ' ',
		'\n','\r','\t', ' ',
		'\n','\r','\t', ' ',
		'\n','\r','\t', ' '
		);

	static const uint8_t lut[][16] __attribute__((aligned (16))) = {
		{   0U,   1U,   2U,   3U,   4U,   5U,   6U,   7U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U },
		{   1U,   2U,   3U,   4U,   5U,   6U,   7U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U },
		...,
		{ 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U, 255U }
	};

	static const uint8_t ipopcnt_lut[] = {
		8U, 7U, 7U, 6U, 7U, 6U, 6U, 5U, 7U, 6U, 6U, 5U, 6U, 5U, 5U, 4U,
		7U, 6U, 6U, 5U, 6U, 5U, 5U, 4U, 6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U,
		7U, 6U, 6U, 5U, 6U, 5U, 5U, 4U, 6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		7U, 6U, 6U, 5U, 6U, 5U, 5U, 4U, 6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U, 4U, 3U, 3U, 2U, 3U, 2U, 2U, 1U,
		7U, 6U, 6U, 5U, 6U, 5U, 5U, 4U, 6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U, 4U, 3U, 3U, 2U, 3U, 2U, 2U, 1U,
		6U, 5U, 5U, 4U, 5U, 4U, 4U, 3U, 5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U,
		5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U, 4U, 3U, 3U, 2U, 3U, 2U, 2U, 1U,
		5U, 4U, 4U, 3U, 4U, 3U, 3U, 2U, 4U, 3U, 3U, 2U, 3U, 2U, 2U, 1U,
		4U, 3U, 3U, 2U, 3U, 2U, 2U, 1U, 3U, 2U, 2U, 1U, 2U, 1U, 1U, 0U
	};

	__m128i c0 = _mm_loadu_si128((const __m128i*)(src +  0));
	__m128i c2 = _mm_loadu_si128((const __m128i*)(src + 16));
	src += 32;
	srclen -= 32U;

	__m128i wm0 = _mm_cmpistrm(whitespaces, c0, _SIDD_UBYTE_OPS | _SIDD_CMP_EQUAL_ANY | _SIDD_BIT_MASK);
	__m128i wm2 = _mm_cmpistrm(whitespaces, c2, _SIDD_UBYTE_OPS | _SIDD_CMP_EQUAL_ANY | _SIDD_BIT_MASK);

	unsigned int mi0 = (unsigned int)_mm_cvtsi128_si32(wm0);
	unsigned int mi2 = (unsigned int)_mm_cvtsi128_si32(wm2);

	if (mi0 | mi2) {
		unsigned int i0 = ipopcnt_lut[mi0 & 255U];
		unsigned int i1 = ipopcnt_lut[mi0 >> 8];
		unsigned int i2 = ipopcnt_lut[mi2 & 255U];
		unsigned int i3 = ipopcnt_lut[mi2 >> 8];

		__m128i c1 = _mm_srli_si128(c0, 8);
		__m128i c3 = _mm_srli_si128(c2, 8);

		c0 = _mm_shuffle_epi8(c0, _mm_load_si128(lut[mi0 & 255U]));
		c1 = _mm_shuffle_epi8(c1, _mm_load_si128(lut[mi0 >> 8]));
		c2 = _mm_shuffle_epi8(c2, _mm_load_si128(lut[mi2 & 255U]));
		c3 = _mm_shuffle_epi8(c3, _mm_load_si128(lut[mi2 >> 8]));
		_mm_storel_epi64((__m128i*)dst, c0);
		dst += i0;
		_mm_storel_epi64((__m128i*)dst, c1);
		dst += i1;
		_mm_storel_epi64((__m128i*)dst, c2);
		dst += i2;
		_mm_storel_epi64((__m128i*)dst, c3);
		dst += i3;
	}
	else {
		_mm_storeu_si128((__m128i*)(dst +  0), c0);
		_mm_storeu_si128((__m128i*)(dst + 16), c2);
		dst += 32;
	}
}

Here are the timings. All throughputs are given for the output buffer which is the same for all variants.
decode: valid base64 input
decode-s: one whitespace every 80 characters (we can see the choice of 80 has an impact on AVX2 decoder for method 1 because it's a multiple of 16 but not 32)
decode-s8: 8 whitespace every 80 characters
decode-d: 1 whitespace before each valid character.

Method 1 seems to be the best for sparse whitespace characters except for AVX2 decoder (that could/should be fixed to handle 8/16 bytes valid input). For handling sparse group of characters or very dense whitespace characters, Method 3 is better.
Real world data analysis would be good to know what case we want to optimize.

For Method 1:

Filling buffer with 10.0 MB of random data...
Testing with buffer size 10 MB, fastest of 100 * 1
AVX2   decode     5279.50 MB/sec
AVX2   decode-s   1587.19 MB/sec
AVX2   decode-s8  1005.11 MB/sec
AVX2   decode-d    226.64 MB/sec
plain  decode     1234.00 MB/sec
plain  decode-s   1180.52 MB/sec
plain  decode-s8   899.77 MB/sec
plain  decode-d    245.90 MB/sec
SSSE3  decode     2941.00 MB/sec
SSSE3  decode-s   2414.34 MB/sec
SSSE3  decode-s8  1198.43 MB/sec
SSSE3  decode-d    210.47 MB/sec
SSE41  decode     2938.98 MB/sec
SSE41  decode-s   2369.73 MB/sec
SSE41  decode-s8  1167.77 MB/sec
SSE41  decode-d    209.58 MB/sec
SSE42  decode     3820.97 MB/sec
SSE42  decode-s   3469.99 MB/sec
SSE42  decode-s8  2009.10 MB/sec
SSE42  decode-d    273.74 MB/sec
AVX    decode     3959.44 MB/sec
AVX    decode-s   3573.91 MB/sec
AVX    decode-s8  2051.51 MB/sec
AVX    decode-d    233.33 MB/sec
Testing with buffer size 1 MB, fastest of 100 * 10
AVX2   decode     5302.67 MB/sec
AVX2   decode-s   1590.81 MB/sec
AVX2   decode-s8  1004.56 MB/sec
AVX2   decode-d    226.81 MB/sec
plain  decode     1238.86 MB/sec
plain  decode-s   1184.43 MB/sec
plain  decode-s8   903.14 MB/sec
plain  decode-d    241.19 MB/sec
SSSE3  decode     2952.08 MB/sec
SSSE3  decode-s   2472.69 MB/sec
SSSE3  decode-s8  1157.22 MB/sec
SSSE3  decode-d    211.32 MB/sec
SSE41  decode     2952.81 MB/sec
SSE41  decode-s   2477.51 MB/sec
SSE41  decode-s8  1201.25 MB/sec
SSE41  decode-d    210.74 MB/sec
SSE42  decode     3831.55 MB/sec
SSE42  decode-s   3487.39 MB/sec
SSE42  decode-s8  2101.31 MB/sec
SSE42  decode-d    275.14 MB/sec
AVX    decode     3967.55 MB/sec
AVX    decode-s   3507.18 MB/sec
AVX    decode-s8  2055.18 MB/sec
AVX    decode-d    225.99 MB/sec
Testing with buffer size 100 KB, fastest of 100 * 100
AVX2   decode     5272.91 MB/sec
AVX2   decode-s   1592.12 MB/sec
AVX2   decode-s8   998.94 MB/sec
AVX2   decode-d    226.41 MB/sec
plain  decode     1237.12 MB/sec
plain  decode-s   1183.57 MB/sec
plain  decode-s8   902.16 MB/sec
plain  decode-d    241.08 MB/sec
SSSE3  decode     2920.62 MB/sec
SSSE3  decode-s   2401.63 MB/sec
SSSE3  decode-s8  1165.97 MB/sec
SSSE3  decode-d    213.04 MB/sec
SSE41  decode     2952.13 MB/sec
SSE41  decode-s   2473.57 MB/sec
SSE41  decode-s8  1170.04 MB/sec
SSE41  decode-d    210.97 MB/sec
SSE42  decode     3826.16 MB/sec
SSE42  decode-s   3484.39 MB/sec
SSE42  decode-s8  1877.99 MB/sec
SSE42  decode-d    274.92 MB/sec
AVX    decode     3860.69 MB/sec
AVX    decode-s   3491.69 MB/sec
AVX    decode-s8  2030.65 MB/sec
AVX    decode-d    222.85 MB/sec
Testing with buffer size 10 KB, fastest of 1000 * 100
AVX2   decode     5213.04 MB/sec
AVX2   decode-s   1608.52 MB/sec
AVX2   decode-s8  1012.05 MB/sec
AVX2   decode-d    231.93 MB/sec
plain  decode     1237.74 MB/sec
plain  decode-s   1184.74 MB/sec
plain  decode-s8   903.57 MB/sec
plain  decode-d    250.86 MB/sec
SSSE3  decode     2942.19 MB/sec
SSSE3  decode-s   2464.90 MB/sec
SSSE3  decode-s8  1197.61 MB/sec
SSSE3  decode-d    219.08 MB/sec
SSE41  decode     2946.40 MB/sec
SSE41  decode-s   2468.99 MB/sec
SSE41  decode-s8  1165.37 MB/sec
SSE41  decode-d    214.67 MB/sec
SSE42  decode     3703.31 MB/sec
SSE42  decode-s   3372.53 MB/sec
SSE42  decode-s8  1814.50 MB/sec
SSE42  decode-d    267.22 MB/sec
AVX    decode     3843.75 MB/sec
AVX    decode-s   3460.58 MB/sec
AVX    decode-s8  2030.02 MB/sec
AVX    decode-d    227.47 MB/sec
Testing with buffer size 1 KB, fastest of 1000 * 1000
AVX2   decode     4314.66 MB/sec
AVX2   decode-s   1562.26 MB/sec
AVX2   decode-s8  1024.11 MB/sec
AVX2   decode-d    233.38 MB/sec
plain  decode     1207.16 MB/sec
plain  decode-s   1129.71 MB/sec
plain  decode-s8   904.50 MB/sec
plain  decode-d    249.83 MB/sec
SSSE3  decode     2714.32 MB/sec
SSSE3  decode-s   2369.40 MB/sec
SSSE3  decode-s8  1203.05 MB/sec
SSSE3  decode-d    219.10 MB/sec
SSE41  decode     2716.16 MB/sec
SSE41  decode-s   2392.42 MB/sec
SSE41  decode-s8  1203.59 MB/sec
SSE41  decode-d    215.04 MB/sec
SSE42  decode     3418.99 MB/sec
SSE42  decode-s   3181.47 MB/sec
SSE42  decode-s8  1904.47 MB/sec
SSE42  decode-d    283.45 MB/sec
AVX    decode     3556.95 MB/sec
AVX    decode-s   3238.04 MB/sec
AVX    decode-s8  1986.58 MB/sec
AVX    decode-d    233.68 MB/sec

For Method 3:

Filling buffer with 10.0 MB of random data...
Testing with buffer size 10 MB, fastest of 100 * 1
AVX2   decode     3230.06 MB/sec
AVX2   decode-s   2741.82 MB/sec
AVX2   decode-s8  2874.97 MB/sec
AVX2   decode-d   1558.49 MB/sec
plain  decode      619.40 MB/sec
plain  decode-s    548.73 MB/sec
plain  decode-s8   548.71 MB/sec
plain  decode-d    420.43 MB/sec
SSSE3  decode     2057.59 MB/sec
SSSE3  decode-s   1807.58 MB/sec
SSSE3  decode-s8  1920.25 MB/sec
SSSE3  decode-d   1257.10 MB/sec
SSE41  decode     2123.90 MB/sec
SSE41  decode-s   1890.92 MB/sec
SSE41  decode-s8  1883.30 MB/sec
SSE41  decode-d   1209.47 MB/sec
SSE42  decode     2622.27 MB/sec
SSE42  decode-s   2366.88 MB/sec
SSE42  decode-s8  2421.09 MB/sec
SSE42  decode-d   1435.30 MB/sec
AVX    decode     2777.55 MB/sec
AVX    decode-s   2419.70 MB/sec
AVX    decode-s8  2480.22 MB/sec
AVX    decode-d   1450.81 MB/sec
Testing with buffer size 1 MB, fastest of 100 * 10
AVX2   decode     3378.80 MB/sec
AVX2   decode-s   2775.84 MB/sec
AVX2   decode-s8  2892.33 MB/sec
AVX2   decode-d   1590.29 MB/sec
plain  decode      626.00 MB/sec
plain  decode-s    580.68 MB/sec
plain  decode-s8   562.96 MB/sec
plain  decode-d    408.17 MB/sec
SSSE3  decode     2191.44 MB/sec
SSSE3  decode-s   1892.64 MB/sec
SSSE3  decode-s8  1861.03 MB/sec
SSSE3  decode-d   1227.95 MB/sec
SSE41  decode     2140.16 MB/sec
SSE41  decode-s   1893.56 MB/sec
SSE41  decode-s8  1911.62 MB/sec
SSE41  decode-d   1226.44 MB/sec
SSE42  decode     2724.52 MB/sec
SSE42  decode-s   2257.47 MB/sec
SSE42  decode-s8  2370.60 MB/sec
SSE42  decode-d   1424.35 MB/sec
AVX    decode     2743.86 MB/sec
AVX    decode-s   2433.86 MB/sec
AVX    decode-s8  2428.08 MB/sec
AVX    decode-d   1408.13 MB/sec
Testing with buffer size 100 KB, fastest of 100 * 100
AVX2   decode     3284.48 MB/sec
AVX2   decode-s   2735.35 MB/sec
AVX2   decode-s8  2813.35 MB/sec
AVX2   decode-d   1574.50 MB/sec
plain  decode      623.97 MB/sec
plain  decode-s    570.76 MB/sec
plain  decode-s8   566.80 MB/sec
plain  decode-d    406.15 MB/sec
SSSE3  decode     2191.73 MB/sec
SSSE3  decode-s   1905.69 MB/sec
SSSE3  decode-s8  1843.39 MB/sec
SSSE3  decode-d   1261.96 MB/sec
SSE41  decode     2190.32 MB/sec
SSE41  decode-s   1938.25 MB/sec
SSE41  decode-s8  1841.31 MB/sec
SSE41  decode-d   1259.89 MB/sec
SSE42  decode     2738.85 MB/sec
SSE42  decode-s   2408.05 MB/sec
SSE42  decode-s8  2430.57 MB/sec
SSE42  decode-d   1437.67 MB/sec
AVX    decode     2818.79 MB/sec
AVX    decode-s   2388.06 MB/sec
AVX    decode-s8  2494.78 MB/sec
AVX    decode-d   1455.20 MB/sec
Testing with buffer size 10 KB, fastest of 1000 * 100
AVX2   decode     3345.58 MB/sec
AVX2   decode-s   2842.44 MB/sec
AVX2   decode-s8  2887.61 MB/sec
AVX2   decode-d   1561.51 MB/sec
plain  decode      634.51 MB/sec
plain  decode-s    591.72 MB/sec
plain  decode-s8   573.85 MB/sec
plain  decode-d    464.49 MB/sec
SSSE3  decode     2182.45 MB/sec
SSSE3  decode-s   1927.53 MB/sec
SSSE3  decode-s8  1933.26 MB/sec
SSSE3  decode-d   1248.62 MB/sec
SSE41  decode     2183.39 MB/sec
SSE41  decode-s   1954.86 MB/sec
SSE41  decode-s8  1935.52 MB/sec
SSE41  decode-d   1247.71 MB/sec
SSE42  decode     2726.89 MB/sec
SSE42  decode-s   2421.89 MB/sec
SSE42  decode-s8  2432.85 MB/sec
SSE42  decode-d   1421.62 MB/sec
AVX    decode     2809.99 MB/sec
AVX    decode-s   2470.29 MB/sec
AVX    decode-s8  2496.32 MB/sec
AVX    decode-d   1432.62 MB/sec
Testing with buffer size 1 KB, fastest of 1000 * 1000
AVX2   decode     2964.24 MB/sec
AVX2   decode-s   2619.61 MB/sec
AVX2   decode-s8  2530.74 MB/sec
AVX2   decode-d   1536.01 MB/sec
plain  decode      621.43 MB/sec
plain  decode-s    588.34 MB/sec
plain  decode-s8   567.04 MB/sec
plain  decode-d    459.67 MB/sec
SSSE3  decode     2011.50 MB/sec
SSSE3  decode-s   1848.21 MB/sec
SSSE3  decode-s8  1764.75 MB/sec
SSSE3  decode-d   1231.03 MB/sec
SSE41  decode     2001.69 MB/sec
SSE41  decode-s   1846.22 MB/sec
SSE41  decode-s8  1765.15 MB/sec
SSE41  decode-d   1229.00 MB/sec
SSE42  decode     2507.66 MB/sec
SSE42  decode-s   2254.18 MB/sec
SSE42  decode-s8  2162.37 MB/sec
SSE42  decode-d   1405.58 MB/sec
AVX    decode     2582.07 MB/sec
AVX    decode-s   2305.40 MB/sec
AVX    decode-s8  2281.94 MB/sec
AVX    decode-d   1414.54 MB/sec

The text was updated successfully, but these errors were encountered:

aqrit · 2017-03-12T07:20:55Z

ssse3 with smaller lut
https://gist.github.com/aqrit/6e73ca6ff52f72a2b121d584745f89f3

izoroth · 2022-02-07T19:33:54Z

Is there any interest in adopting this PR?

We are looking into adopting this library, and ran into an issue with some keys we expect to decode have \n characters.

aklomp · 2022-02-10T00:12:36Z

@izoroth Short answer: not currently, no.

Long answer: Well, it's not really a PR, it's a series of sketches of what a despacing algorithm might look like. There's no definite patchset to merge, and if there was, the patches would probably not apply on top of the current master branch. There would also be API changes to consider. And there is a discussion to be had about whether to optimize for sparse whitespace or dense whitespace.

I think that whitespace filtering could make sense in this library as an opt-in feature, but it's not fleshed out enough yet.

mayeut mentioned this issue Nov 6, 2016

[Question] Invalid input data handling ? #27

Open

aklomp mentioned this issue Nov 22, 2023

v0.5.1 breaks base64 -d on Alpine Linux (musl libc) #126

Closed

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Whitespace character filtering #33

Whitespace character filtering #33

mayeut commented Nov 6, 2016 •

edited

aqrit commented Mar 12, 2017

izoroth commented Feb 7, 2022

aklomp commented Feb 10, 2022

Whitespace character filtering #33

Whitespace character filtering #33

Comments

mayeut commented Nov 6, 2016 • edited

aqrit commented Mar 12, 2017

izoroth commented Feb 7, 2022

aklomp commented Feb 10, 2022

mayeut commented Nov 6, 2016 •

edited