From 85be877925ddbf34f74a1229f3ca1716bb6170dc Mon Sep 17 00:00:00 2001 From: Behdad Esfahbod Date: Wed, 1 Feb 2023 20:00:43 -0700 Subject: [PATCH] [layout] Limit how far we skip when looking back See comments. --- src/hb-ot-layout-gsubgpos.hh | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh index c17bf92..712e307 100644 --- a/src/hb-ot-layout-gsubgpos.hh +++ b/src/hb-ot-layout-gsubgpos.hh @@ -535,7 +535,19 @@ struct hb_ot_apply_context_t : bool prev () { assert (num_items > 0); - while (idx > num_items - 1) + /* The alternate condition below is faster at string boundaries, + * but produces subpar "unsafe-to-concat" values. */ + unsigned stop = num_items - 1; + if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT) + stop = 1 - 1; + + /* When looking back, limit how far we search; this function is mostly + * used for looking back for base glyphs when attaching marks. If we + * don't limit, we can get O(n^2) behavior where n is the number of + * consecutive marks. */ + stop = (unsigned) hb_max ((int) stop, (int) idx - HB_MAX_CONTEXT_LENGTH); + + while (idx > stop) { idx--; const hb_glyph_info_t &info = c->buffer->out_info[idx]; -- 2.33.0