make pregexec() handle zero-length strings again

embed.fnc

@@ -2713,7 +2713,7 @@ Adhp	|REGEXP *|pregcomp	|NN SV * const pattern			\
 				|const U32 flags
 Adhp	|I32	|pregexec	|NN REGEXP * const prog 		\
 				|MPTR char *stringarg			\
-				|EPTR char *strend			\
+				|EPTRQ char *strend			\
 				|SPTR char *strbeg			\
 				|SSize_t minend 			\
 				|NN SV *screamer			\

ext/XS-APItest/APItest.pm

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 use Carp;
 
-our $VERSION = '1.47';
+our $VERSION = '1.48';
 
 require XSLoader;
 

ext/XS-APItest/APItest.xs

@@ -4780,6 +4780,29 @@ CODE:
 OUTPUT:
     RETVAL
 
+ # provide access to pregexec, except replace pointers within the
+ # string with offsets from the start of the string
+
+I32
+callpregexec(SV *prog, STRLEN stringarg, STRLEN strend, I32 minend, SV *sv, U32 nosave)
+CODE:
+    {
+        STRLEN len;
+        char *strbeg;
+        if (SvROK(prog))
+            prog = SvRV(prog);
+        strbeg = SvPV_force(sv, len);
+        RETVAL = pregexec((REGEXP *)prog,
+                            strbeg + stringarg,
+                            strbeg + strend,
+                            strbeg,
+                            minend,
+                            sv,
+                            nosave);
+    }
+OUTPUT:
+    RETVAL
+
 void
 lexical_import(SV *name, CV *cv)
     CODE:

ext/XS-APItest/t/callregexec.t

@@ -1,6 +1,6 @@
 #!perl
 
-# test CALLREGEXEC()
+# test CALLREGEXEC() and pregexec()
 # (currently it just checks that it handles non-\0 terminated strings;
 # full tests haven't been added yet)
 
@@ -10,7 +10,7 @@ use strict;
 use XS::APItest;
 *callregexec = *XS::APItest::callregexec;
 
-use Test::More tests => 48;
+use Test::More tests => 75;
 
 # Test that the regex engine can handle strings without terminating \0
 # XXX This is by no means comprehensive; it doesn't test all ops, nor all
@@ -34,6 +34,8 @@ sub try {
     my $bytes = do { use bytes; length $str1 };
     ok  !!$exp == !!callregexec($re, 0, $bytes, 0, $str, 0),
 	    "$desc callregexec";
+    ok  !!$exp == !!callpregexec($re, 0, $bytes, 0, $str, 0),
+	    "$desc callpregexec";
 }
 
 
@@ -62,4 +64,5 @@ sub try {
     try "ab\t",        qr/^.+\h/,         0, 'HORIZWS';
     try "abx",         qr/^.+\H/,         1, 'NHORIZWS';
     try "abx",         qr/a.*x/,          0, 'CURLY';
+    try "",            qr/x?/,            1, 'empty';
 }