Greatly simplify and speed up regexec0() using REG_STARTEND.

This is a 15 year old freebsd extension (presumably thus also available on
MacOS) that glibc adopted in 2004, uClibc adopted in 2005, and bionic
supports. The only thing that DOESN'T support it is musl, once again
because its maintainer explicitly decided not to
(https://www.openwall.com/lists/musl/2013/01/15/26), so add an #ifdef
to let musl stay uniquely broken. (It'll stop at first NUL, everything
else can match NULs).

Finally fixes "s/x/y/g on a megabyte line of x's takes forever" issue.

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/sed.test b/tests/sed.test
index 6b27fff8..e5ec11bd 100755
--- a/tests/sed.test
+++ b/tests/sed.test
@@ -176,4 +176,10 @@ testing '\n with empty capture' \
 testing '\n too high' \
     'sed -E "s/(.*)/\2/p" 2>/dev/null || echo OK' "OK\n" "" "foo"
 
+# Performance test
+X=x; Y=20; while [ $Y -gt 0 ]; do X=$X$X; Y=$(($Y-1)); done
+testing 'megabyte s/x/y/g (5 sec timeout)' "timeout 5 sed 's/x/y/g' | sha1sum" \
+  '138c1fa7c3f64186203b0192fb4abdb33cb4e98a  -\n' '' "$X\n"
+unset X Y
+
 # -i with $ last line test