+# ifdef PERL_NEW_COPY_ON_WRITE
+# define SvCANCOW(sv) \
+ (SvIsCOW(sv) \
+ ? SvLEN(sv) ? CowREFCNT(sv) != SV_COW_REFCNT_MAX : 1 \
+ : (SvFLAGS(sv) & CAN_COW_MASK) == CAN_COW_FLAGS \
+ && SvCUR(sv)+1 < SvLEN(sv))
+ /* Note: To allow 256 COW "copies", a refcnt of 0 means 1. */
+# define CowREFCNT(sv) (*(U8 *)(SvPVX(sv)+SvLEN(sv)-1))
+# define SV_COW_REFCNT_MAX ((1 << sizeof(U8)*8) - 1)
+# ifndef SV_COW_THRESHOLD
+# define SV_COW_THRESHOLD 0 /* min string length for cow */
+# endif
+# ifndef SV_COWBUF_THRESHOLD
+# define SV_COWBUF_THRESHOLD 1250 /* min string length for cow */
+# endif /* over existing buffer */
+# define CAN_COW_MASK (SVf_POK|SVf_ROK|SVp_POK|SVf_FAKE| \
+ SVf_OOK|SVf_BREAK|SVf_READONLY)
+# endif