Improve documentation for is_gv_magical, and split the switch

statement into 2 parts, lengths > 1 and lengths <= 1
This should cause most variables (lower case, multicharacter)
to escape the function without passing through a switch table.

p4raw-id: //depot/perl@23720

diff --git a/gv.c b/gv.c
index b68f212..d84042d 100644 (file)
--- a/gv.c
+++ b/gv.c
@@ -1822,110 +1822,124 @@ created even in rvalue contexts.
 C<flags> is not used at present but available for future extension to
 allow selecting particular classes of magical variable.
 
+Currently assumes that C<name> is NUL terminated (as well as len being valid).
+This assumption is met by all callers within the perl core, which all pass
+pointers returned by SvPV.
+
 =cut
 */
 bool
 Perl_is_gv_magical(pTHX_ char *name, STRLEN len, U32 flags)
 {
-    if (!len)
-       return FALSE;
-
-    switch (*name) {
-    case 'I':
-       if (len == 3 && strEQ(name, "ISA"))
-           goto yes;
-       break;
-    case 'O':
-       if (len == 8 && strEQ(name, "OVERLOAD"))
-           goto yes;
-       break;
-    case 'S':
-       if (len == 3 && strEQ(name, "SIG"))
-           goto yes;
-       break;
-    case '\017':   /* $^O & $^OPEN */
-       if (len == 1
-           || (len == 4 && strEQ(name, "\017PEN")))
-       {
-           goto yes;
-       }
-       break;
-    case '\025':
-        if (len > 1 && strEQ(name, "\025NICODE"))
-           goto yes;
-    case '\027':   /* $^W & $^WARNING_BITS */
-       if (len == 1
-           || (len == 12 && strEQ(name, "\027ARNING_BITS"))
-           )
+    if (len > 1) {
+       switch (*name) {
+       case 'I':
+           if (len == 3 && strEQ(name, "ISA"))
+               goto yes;
+           break;
+       case 'O':
+           if (len == 8 && strEQ(name, "OVERLOAD"))
+               goto yes;
+           break;
+       case 'S':
+           if (len == 3 && strEQ(name, "SIG"))
+               goto yes;
+           break;
+           /* Using ${^...} variables is likely to be sufficiently rare that
+              it seems sensible to avoid the space hit of also checking the
+              length.  */
+       case '\017':   /* ${^OPEN} */
+           if (strEQ(name, "\017PEN"))
+               goto yes;
+           break;
+       case '\024':   /* ${^TAINT} */
+           if (strEQ(name, "\024AINT"))
+               goto yes;
+           break;
+       case '\025':    /* ${^UNICODE} */
+           if (strEQ(name, "\025NICODE"))
+               goto yes;
+           break;
+       case '\027':   /* ${^WARNING_BITS} */
+           if (strEQ(name, "\027ARNING_BITS"))
+               goto yes;
+           break;
+       case '1':
+       case '2':
+       case '3':
+       case '4':
+       case '5':
+       case '6':
+       case '7':
+       case '8':
+       case '9':
        {
-           goto yes;
-       }
-       break;
-
-    case '&':
-    case '`':
-    case '\'':
-    case ':':
-    case '?':
-    case '!':
-    case '-':
-    case '#':
-    case '[':
-    case '^':
-    case '~':
-    case '=':
-    case '%':
-    case '.':
-    case '(':
-    case ')':
-    case '<':
-    case '>':
-    case ',':
-    case '\\':
-    case '/':
-    case '|':
-    case '+':
-    case ';':
-    case ']':
-    case '\001':   /* $^A */
-    case '\003':   /* $^C */
-    case '\004':   /* $^D */
-    case '\005':   /* $^E */
-    case '\006':   /* $^F */
-    case '\010':   /* $^H */
-    case '\011':   /* $^I, NOT \t in EBCDIC */
-    case '\014':   /* $^L */
-    case '\016':   /* $^N */
-    case '\020':   /* $^P */
-    case '\023':   /* $^S */
-    case '\026':   /* $^V */
-       if (len == 1)
-           goto yes;
-       break;
-    case '\024':   /* $^T, ${^TAINT} */
-        if (len == 1 || strEQ(name, "\024AINT"))
-            goto yes;
-        break;
-    case '1':
-    case '2':
-    case '3':
-    case '4':
-    case '5':
-    case '6':
-    case '7':
-    case '8':
-    case '9':
-       if (len > 1) {
            char *end = name + len;
            while (--end > name) {
                if (!isDIGIT(*end))
                    return FALSE;
            }
+           goto yes;
+       }
+       }
+    } else {
+       /* Because we're already assuming that name is NUL terminated
+          below, we can treat an empty name as "\0"  */
+       switch (*name) {
+       case '&':
+       case '`':
+       case '\'':
+       case ':':
+       case '?':
+       case '!':
+       case '-':
+       case '#':
+       case '[':
+       case '^':
+       case '~':
+       case '=':
+       case '%':
+       case '.':
+       case '(':
+       case ')':
+       case '<':
+       case '>':
+       case ',':
+       case '\\':
+       case '/':
+       case '|':
+       case '+':
+       case ';':
+       case ']':
+       case '\001':   /* $^A */
+       case '\003':   /* $^C */
+       case '\004':   /* $^D */
+       case '\005':   /* $^E */
+       case '\006':   /* $^F */
+       case '\010':   /* $^H */
+       case '\011':   /* $^I, NOT \t in EBCDIC */
+       case '\014':   /* $^L */
+       case '\016':   /* $^N */
+       case '\017':   /* $^O */
+       case '\020':   /* $^P */
+       case '\023':   /* $^S */
+       case '\024':   /* $^T */
+       case '\026':   /* $^V */
+       case '\027':   /* $^W */
+       case '1':
+       case '2':
+       case '3':
+       case '4':
+       case '5':
+       case '6':
+       case '7':
+       case '8':
+       case '9':
+       yes:
+           return TRUE;
+       default:
+           break;
        }
-    yes:
-       return TRUE;
-    default:
-       break;
     }
     return FALSE;
 }