39 lines
1.4 KiB
Diff
39 lines
1.4 KiB
Diff
From 85be877925ddbf34f74a1229f3ca1716bb6170dc Mon Sep 17 00:00:00 2001
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From: Behdad Esfahbod <behdad@behdad.org>
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Date: Wed, 1 Feb 2023 20:00:43 -0700
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Subject: [PATCH] [layout] Limit how far we skip when looking back
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See comments.
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---
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src/hb-ot-layout-gsubgpos.hh | 14 +++++++++++++-
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1 file changed, 13 insertions(+), 1 deletion(-)
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diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
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index c9750ff..b83f49e 100644
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--- a/src/hb-ot-layout-gsubgpos.hh
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+++ b/src/hb-ot-layout-gsubgpos.hh
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@@ -560,7 +560,19 @@ struct hb_ot_apply_context_t :
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bool prev (unsigned *unsafe_from = nullptr)
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{
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assert (num_items > 0);
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- while (idx > num_items - 1)
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+ /* The alternate condition below is faster at string boundaries,
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+ * but produces subpar "unsafe-to-concat" values. */
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+ unsigned stop = num_items - 1;
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+ if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT)
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+ stop = 1 - 1;
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+
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+ /* When looking back, limit how far we search; this function is mostly
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+ * used for looking back for base glyphs when attaching marks. If we
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+ * don't limit, we can get O(n^2) behavior where n is the number of
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+ * consecutive marks. */
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+ stop = (unsigned) hb_max ((int) stop, (int) idx - HB_MAX_CONTEXT_LENGTH);
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+
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+ while (idx > stop)
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{
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idx--;
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const hb_glyph_info_t &info = c->buffer->out_info[idx];
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--
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2.33.0
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