Try to port set_digest

[LaurenzV]

Let's see how it goes.

[LaurenzV]

@behdad In hb_set_digest_combinter_t, is

bool add_range (hb_codepoint_t a, hb_codepoint_t b)
  {
    return (int) head.add_range (a, b) | (int) tail.add_range (a, b);
  }

just

bool add_range (hb_codepoint_t a, hb_codepoint_t b)
  {
    return head.add_range || tail.add_range (a, b);
  }

or am I missing something?

EDIT: Nevermind, the second one would short-circuit while the first one would not, I think.

[LaurenzV]

@RazrFalcon So, turns out we actually have something similar to digest set already, I just didn't notice because it was named differently. :p But it was only used in two locations. Anyway, I replaced it with the harfbuzz set digest implementation and I'm seeing some nice speedups already! I'll see whether I can find the remaining places where it's used in harfbuzz as well.

One thing to note is that I'm not sure I'll be able to replicate the harfbuzz structure 1:1, because in harfbuzz there is this accelerator wrapper struct as well as Proxy, and I'm not sure if it will be easy to port.

Test Name	Before	After
arabic::paragraph_long::rb	392520.8	338027.15
arabic::paragraph_medium::rb	231291.67	190327.6
arabic::paragraph_short::rb	77015.17	64271.48
arabic::sentence_1::rb	54922.92	43420.13
arabic::sentence_2::rb	55653.17	45505.09
arabic::word_1::rb	16283.12	10325.39
arabic::word_2::rb	17411.95	11588.63
arabic::word_3::rb	16523.29	10618.7
english::aat_paragraph_long::rb	497358.4	504909.64
english::aat_sentence_1::rb	58580.37	58986.61
english::aat_word_1::rb	4393.1	4524.62
english::long_zalgo::rb	1870320.9	1720540.6
english::paragraph_long::rb	456722.9	378100
english::paragraph_long_mono::rb	79397.35	79218.18
english::paragraph_medium::rb	331425	268264.41
english::paragraph_short::rb	211846.53	164255.83
english::sentence_1::rb	125274.98	92912.97
english::sentence_2::rb	115765.27	85812.92
english::sentence_mono::rb	12664.62	12504.7
english::short_zalgo::rb	152888.46	119047.93
english::variations::rb	582909.11	418908.35
english::variations_default::rb	538897.93	417473.97
english::word_1::rb	74295.13	48810.42
english::word_2::rb	96590.96	50727.23
english::word_3::rb	74267.09	48499.26
english::word_4::rb	76657.63	50706.13
hebrew::paragraph_long_1::rb	302007.55	223193.03
hebrew::paragraph_long_2::rb	449438.54	350977.1
hebrew::paragraph_medium::rb	76569.64	59700.3
hebrew::sentence_1::rb	31902.71	24542.92
hebrew::sentence_2::rb	25034.39	18634.87
hebrew::word_1::rb	9316.79	6817.56
hebrew::word_2::rb	9340.54	6853.35
hindi::aat_paragraph_long::rb	1408535.94	1340325.1
hindi::aat_sentence::rb	203805.53	174498.98
hindi::aat_word::rb	47851.74	23387.5
hindi::paragraph_long::rb	1018933.32	874204.2
hindi::paragraph_medium::rb	645542.71	550805.22
hindi::paragraph_short::rb	369729.17	302540.62
hindi::sentence_1::rb	169481.64	135329.17
hindi::sentence_2::rb	162120.49	120293.07
hindi::word_1::rb	68044.56	48514.48
hindi::word_2::rb	67839.84	49835.55
khmer::aat_paragraph_long_1::rb	777954.2	729962.6
khmer::aat_sentence_1::rb	78639.4	68349.99
khmer::aat_word_1::rb	20644.61	13328.75
khmer::paragraph_long_1::rb	753512.5	619012.4
khmer::paragraph_long_2::rb	902437.52	754854.1
khmer::paragraph_medium::rb	433292.18	353707.28
khmer::sentence_1::rb	58932.91	42132.06
khmer::sentence_2::rb	59866.52	46493.28
khmer::word_1::rb	25951.28	19585.42
khmer::word_2::rb	29661.01	22463.33
khmer::word_3::rb	26616.51	20344.21
myanmar::aat_paragraph_long::rb	2488008.33	2493779.15
myanmar::aat_sentence_1::rb	100067.26	95012.7
myanmar::aat_word_1::rb	11847.01	9663.62
myanmar::paragraph_long::rb	3104907.3	2924845.8
myanmar::paragraph_medium::rb	1182590.62	1105495.85
myanmar::paragraph_short::rb	257289.93	232050
myanmar::sentence_1::rb	259715.62	236104.17
myanmar::sentence_2::rb	348687.5	324939.6
myanmar::word_1::rb	25923.36	18480.59
myanmar::word_2::rb	26585	18805.55
thai::paragraph_long::rb	406404.17	369447.66
thai::paragraph_medium::rb	131565.62	114900.68
thai::paragraph_short::rb	52665.87	45863.39
thai::sentence_1::rb	41688.02	35667.65
thai::word_1::rb	11326.98	8625.52
thai::word_2::rb	12161.12	9092.81

[RazrFalcon]

Great!

So, turns out we actually have something similar to digest set already, I just didn't notice because it was named differently.

Yes, looks like laurmaedje decided to implement it that way. The whole GSUB/GPOS/OpenType layout was written by him.
Eventually I moved tables parsing from RB to ttf-parser, to make RB parsing-free, but everything else was left as is.

[behdad]

This looks great!

These are places that HB uses the set-digest:

• Checking the glyph against the lookup's digest of all Coverages in its subtables,
• Then checking the glyph against each sublookup's digest before trying,
• A whole-buffer digest is checked against the lookup digest to possibly skip the lookup completely,
• GDEF MarkFilteringSets keep a digest of each set for faster lookup. This sped up Duployan-Regular [0] by 45%!
• kern table keeps a digest of left and right glyphs,
• morx table keeps a digest of all glyphs that have a non-zero class in the SubChain's state machine.

[0] Available from https://github.com/harfbuzz/harfbuzz-monster-fonts

[LaurenzV]

Thanks!

[behdad]

With the buffer digest, note that you need to:

• Recalculate the digest after shaper functions that modify the buffer,
  https://github.com/harfbuzz/harfbuzz/blob/e079dd20304bacd8d753eee2ceacbaa1a3978a34/src/hb-ot-layout.cc#L2050

• Add new glyphs to the digest as they are added in GSUB.
  https://github.com/harfbuzz/harfbuzz/blob/e079dd20304bacd8d753eee2ceacbaa1a3978a34/src/hb-ot-layout-gsubgpos.hh#L839

[LaurenzV]

Yep, no worries, those are already included. 😄

[LaurenzV]

Alright, AAT and GDEF are a bit trickier unfortunately because from what I can tell ttf-parser doesn't always expose the necessary information on the glyph coverage, so I guess let's leave it at that for now. I've added TODOs in the appropriate places.

We still have some nice overall performance improvements!

[RazrFalcon]

Thanks!