Extract minimum PV buffer/AV element size to common definitions

In a nutshell, for a long time the minimum PV length (hardcoded
in Perl_sv_grow) has been 10 bytes and the minimum AV array size
(hardcoded in av_extend_guts) has been 4 elements.

These numbers have been used elsewhere for consistency (e.g.
Perl_sv_grow_fresh) in the past couple of development cycles.
Having a standard definition, rather than hardcoding in multiple
places, is more maintainable. This commit therefore introduces
into perl.h:

    PERL_ARRAY_NEW_MIN_KEY
    PERL_STRLEN_NEW_MIN

(Note: Subsequent commit(s) will actually change the values.)

1 files changed, 17 insertions, 0 deletions

diff --git a/perl.h b/perl.h
index 1debb2c087..4fbc0abe7a 100644
--- a/perl.h
+++ b/perl.h
@@ -1593,6 +1593,23 @@ Use L</UV> to declare variables of the maximum usable size on this platform.
 
 #define MEM_SIZE Size_t
 
+/* av_extend and analogues enforce a minimum number of array elements.
+ * This has been 4 elements (so a minimum key size of 3) for a long
+ * time, but the rationale behind this seems to have been lost to the
+ * mists of time. */
+#ifndef PERL_ARRAY_NEW_MIN_KEY
+#define PERL_ARRAY_NEW_MIN_KEY 3
+#endif
+
+/* Functions like Perl_sv_grow mandate a minimum string size.
+ * This was 10 bytes for a long time, the rationale for which seems lost
+ * to the mists of time. However, since this does not correlate to what
+ * modern malloc implementations will actually return, it can be revised
+ * to be more appropriate. */
+#ifndef PERL_STRLEN_NEW_MIN
+#define PERL_STRLEN_NEW_MIN 10
+#endif
+
 /* Round all values passed to malloc up, by default to a multiple of
    sizeof(size_t)
 */