From 2bdc92d6ec8460f65bfe9c0af82a90814b397613 Mon Sep 17 00:00:00 2001
From: Kyryl Melekhin <k.melekhin@gmail.com>
Date: Sat, 2 Oct 2021 09:27:54 +0000
Subject: [PATCH] optimize alt epsilon transition offsets

---
 pike.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/pike.c b/pike.c
index 669a14d..5fc7dfd 100644
--- a/pike.c
+++ b/pike.c
@@ -191,6 +191,7 @@ static int _compilecode(const char **re_loc, rcode *prog, int sizecode)
 	int *code = sizecode ? NULL : prog->insts;
 	int start = PC, term = PC;
 	int alt_label = 0, c;
+	int alt_stack[5000], altc = 0;
 
 	for (; *re && *re != ')';) {
 		switch (*re) {
@@ -362,7 +363,7 @@ static int _compilecode(const char **re_loc, rcode *prog, int sizecode)
 			break;
 		case '|':
 			if (alt_label)
-				EMIT(alt_label, REL(alt_label, PC) + 1);
+				alt_stack[altc++] = alt_label;
 			INSERT_CODE(start, 3, PC);
 			EMIT(PC++, JMP);
 			alt_label = PC++;
@@ -386,8 +387,13 @@ static int _compilecode(const char **re_loc, rcode *prog, int sizecode)
 		}
 		uc_len(c, re) re += c;
 	}
-	if (alt_label)
+	if (alt_label) {
 		EMIT(alt_label, REL(alt_label, PC) + 1);
+		for (int alts = altc; altc; altc--) {
+			int at = alt_stack[alts-altc]+altc*3;
+			EMIT(at, REL(at, PC) + 1);
+		}
+	}
 	*re_loc = re;
 	return RE_SUCCESS;
 syntax_error: