From e9a43ed4ae9c9c4d6f4e250e4f929ac9602d7452 Mon Sep 17 00:00:00 2001 From: Akim Demaille Date: Sun, 11 Oct 2020 15:41:17 +0200 Subject: [PATCH] ielr: make some conditions about items easier to understand MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Checking that an item index is > 1 means ruling out `$accept: • input $end` and `$accept: input • $end`. But actually only the latter is possible there, i.e., we're checking whether this item is about a successor of a (kernel) item of the initial state ($accept: input • $end). * src/ielr.c (is_successor_of_initial_item): Use a variable to name this condition. --- src/ielr.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/ielr.c b/src/ielr.c index 26754a72..9490ec72 100644 --- a/src/ielr.c +++ b/src/ielr.c @@ -413,7 +413,10 @@ ielr_item_has_lookahead (state *s, symbol_number lhs, size_t item, didn't change this test to an aver just in case the usage of this function evolves to need those two cases. In both cases, the current implementation returns the right result. */ - if (s->items[item] > 1) + aver (s->items[item] != 1); + const bool is_successor_of_initial_item = s->items[item] <= 1; + aver (!is_successor_of_initial_item); + if (!is_successor_of_initial_item) { /* If the LHS symbol of this item isn't known (because this is a top-level invocation), go get it. */ @@ -622,9 +625,11 @@ ielr_compute_lookaheads (bitsetv follow_kernel_items, bitsetv always_follows, a special case to avoid the - 2 below, but the next successor can be handled fine without special casing it. */ aver (t->items[t_item] != 0); - if (t->items[t_item] > 1 + const bool is_successor_of_initial_item = t->items[t_item] <= 1; + if (!is_successor_of_initial_item && !bitset_empty_p (lookahead_filter[t_item])) { + /* Is this kernel item next to the beginning of the RHS? */ if (item_number_is_rule_number (ritem[t->items[t_item] - 2])) ielr_compute_goto_follow_set ( follow_kernel_items, always_follows, s,