handy.h: Comment memEQs and memNEs

[perl5.git] / av.c

diff --git a/av.c b/av.c
index cb99ceb..21828a9 100644 (file)
--- a/av.c
+++ b/av.c
@@ -87,6 +87,10 @@ Perl_av_extend_guts(pTHX_ AV *av, SSize_t key, SSize_t *maxp, SV ***allocp,
 {
     PERL_ARGS_ASSERT_AV_EXTEND_GUTS;
 
+    if (key < -1) /* -1 is legal */
+        Perl_croak(aTHX_
+            "panic: av_extend_guts() negative count (%"IVdf")", (IV)key);
+
     if (key > *maxp) {
        SV** ary;
        SSize_t tmp;
@@ -240,10 +244,13 @@ S_adjust_index(pTHX_ AV *av, const MAGIC *mg, SSize_t *keyp)
 SV**
 Perl_av_fetch(pTHX_ AV *av, SSize_t key, I32 lval)
 {
+    SSize_t neg;
+    SSize_t size;
+
     PERL_ARGS_ASSERT_AV_FETCH;
     assert(SvTYPE(av) == SVt_PVAV);
 
-    if (SvRMAGICAL(av)) {
+    if (UNLIKELY(SvRMAGICAL(av))) {
         const MAGIC * const tied_magic
            = mg_find((const SV *)av, PERL_MAGIC_tied);
         if (tied_magic || mg_find((const SV *)av, PERL_MAGIC_regdata)) {
@@ -264,23 +271,23 @@ Perl_av_fetch(pTHX_ AV *av, SSize_t key, I32 lval)
         }
     }
 
-    if (key < 0) {
-       key += AvFILL(av) + 1;
-       if (key < 0)
+    neg  = (key < 0);
+    size = AvFILLp(av) + 1;
+    key += neg * size; /* handle negative index without using branch */
+
+    /* the cast from SSize_t to Size_t allows both (key < 0) and (key >= size)
+     * to be tested as a single condition */
+    if ((Size_t)key >= (Size_t)size) {
+       if (UNLIKELY(neg))
            return NULL;
+        goto emptyness;
     }
 
-    if (key > AvFILLp(av) || !AvARRAY(av)[key]) {
+    if (!AvARRAY(av)[key]) {
       emptyness:
        return lval ? av_store(av,key,newSV(0)) : NULL;
     }
 
-    if (AvREIFY(av)
-            && (!AvARRAY(av)[key]      /* eg. @_ could have freed elts */
-                || SvIS_FREED(AvARRAY(av)[key]))) {
-       AvARRAY(av)[key] = NULL;        /* 1/2 reify */
-       goto emptyness;
-    }
     return &AvARRAY(av)[key];
 }
 
@@ -432,11 +439,15 @@ Perl_av_make(pTHX_ SSize_t size, SV **strp)
 /*
 =for apidoc av_clear
 
-Clears an array, making it empty.  Does not free the memory C<av> uses to
-store its list of scalars.  If any destructors are triggered as a result,
-C<av> itself may be freed when this function returns.
+Frees the all the elements of an array, leaving it empty.
+The XS equivalent of C<@array = ()>.  See also L</av_undef>.
 
-Perl equivalent: C<@myarray = ();>.
+Note that it is possible that the actions of a destructor called directly
+or indirectly by freeing an element of the array could cause the reference
+count of the array itself to be reduced (e.g. by deleting an entry in the
+symbol table). So it is a possibility that the AV could have been freed
+(or even reallocated) on return from the call unless you hold a reference
+to it.
 
 =cut
 */
@@ -496,9 +507,13 @@ Perl_av_clear(pTHX_ AV *av)
 /*
 =for apidoc av_undef
 
-Undefines the array.  Frees the memory used by the av to store its list of
-scalars.  If any destructors are triggered as a result, C<av> itself may
-be freed.
+Undefines the array. The XS equivalent of C<undef(@array)>.
+
+As well as freeing all the elements of the array (like C<av_clear()>), this
+also frees the memory used by the av to store its list of scalars.
+
+See L</av_clear> for a note about the array possibly being invalid on
+return.
 
 =cut
 */
@@ -555,8 +570,8 @@ Perl_av_create_and_push(pTHX_ AV **const avp, SV *const val)
 /*
 =for apidoc av_push
 
-Pushes an SV onto the end of the array.  The array will grow automatically
-to accommodate the addition.  This takes ownership of one reference count.
+Pushes an SV (transferring control of one reference count) onto the end of the
+array.  The array will grow automatically to accommodate the addition.
 
 Perl equivalent: C<push @myarray, $elem;>.