Create and use single_1bit_pos32()

This moves the code from regcomp.c to inline.h that calculates the
position of the lone set bit in a U32.  This is in preparation for use
by other call sites.

embed.fnc

@@ -1141,6 +1141,7 @@ ATdmoR	|bool	|is_utf8_invariant_string|NN const U8* const s		    \
 ATidRp	|bool	|is_utf8_invariant_string_loc|NN const U8* const s	    \
 		|STRLEN len						    \
 		|NULLOK const U8 ** ep
+CTiRp	|unsigned|single_1bit_pos32|U32 word
 #ifndef EBCDIC
 CTiRp	|unsigned int|variant_byte_number|PERL_UINTMAX_T word
 #endif

embed.h

@@ -561,6 +561,7 @@
 #define set_context		Perl_set_context
 #define setdefout(a)		Perl_setdefout(aTHX_ a)
 #define share_hek(a,b,c)	Perl_share_hek(aTHX_ a,b,c)
+#define single_1bit_pos32	Perl_single_1bit_pos32
 #define sortsv(a,b,c)		Perl_sortsv(aTHX_ a,b,c)
 #define sortsv_flags(a,b,c,d)	Perl_sortsv_flags(aTHX_ a,b,c,d)
 #define stack_grow(a,b,c)	Perl_stack_grow(aTHX_ a,b,c)

globvar.sym

@@ -12,6 +12,7 @@ PL_c9_utf8_dfa_tab
 PL_charclass
 PL_check
 PL_core_reg_engine
+PL_deBruijn_bitpos_tab32
 PL_EXACTFish_bitmask
 PL_EXACT_REQ8_bitmask
 PL_extended_utf8_dfa_tab

inline.h

@@ -664,6 +664,25 @@ Perl_is_utf8_invariant_string_loc(const U8* const s, STRLEN len, const U8 ** ep)
     return TRUE;
 }
 
+PERL_STATIC_INLINE unsigned
+Perl_single_1bit_pos32(U32 word)
+{
+    /* Given a 32-bit word known to contain all zero bits except one 1 bit,
+     * find and return the 1's position: 0..31 */
+
+#ifdef PERL_CORE    /* macro not exported */
+    ASSUME(isPOWER_OF_2(word));
+#else
+    ASSUME(word && (word & (word-1)) == 0);
+#endif
+
+    /* The position of the only set bit in a word can be quickly calculated
+     * using deBruijn sequences.  See for example
+     * https://en.wikipedia.org/wiki/De_Bruijn_sequence */
+    return PL_deBruijn_bitpos_tab32[(word * PERL_deBruijnMagic32_)
+                                                    >> PERL_deBruijnShift32_];
+}
+
 #ifndef EBCDIC
 
 PERL_STATIC_INLINE unsigned int

perl.h

@@ -5842,6 +5842,13 @@ PL_valid_types_IV_set[] = { 0, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1 };
 EXTCONST bool
 PL_valid_types_NV_set[] = { 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0 };
 
+EXTCONST U8
+PL_deBruijn_bitpos_tab32[] = {
+    /* https://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn */
+    0,   1, 28,  2, 29, 14, 24,  3, 30, 22, 20, 15, 25, 17,  4,  8,
+    31, 27, 13, 23, 21, 19, 16,  7, 26, 12, 18,  6, 11,  5, 10,  9
+};
+
 #else
 
 EXTCONST bool PL_valid_types_IVX[];
@@ -5850,9 +5857,14 @@ EXTCONST bool PL_valid_types_PVX[];
 EXTCONST bool PL_valid_types_RV[];
 EXTCONST bool PL_valid_types_IV_set[];
 EXTCONST bool PL_valid_types_NV_set[];
+EXTCONST U8   PL_deBruijn_bitpos_tab32[];
 
 #endif
 
+/* The constants for using PL_deBruijn_bitpos_tab */
+#define PERL_deBruijnMagic32_  0x077CB531
+#define PERL_deBruijnShift32_  27
+
 /* In C99 we could use designated (named field) union initializers.
  * In C89 we need to initialize the member declared first.
  * In C++ we need extern C initializers.

proto.h

@@ -3246,6 +3246,12 @@ PERL_CALLCONV Signal_t	Perl_sighandler1(int sig);
 #define PERL_ARGS_ASSERT_SIGHANDLER1
 PERL_CALLCONV Signal_t	Perl_sighandler3(int sig, Siginfo_t *info, void *uap);
 #define PERL_ARGS_ASSERT_SIGHANDLER3
+#ifndef PERL_NO_INLINE_FUNCTIONS
+PERL_STATIC_INLINE unsigned	Perl_single_1bit_pos32(U32 word)
+			__attribute__warn_unused_result__;
+#define PERL_ARGS_ASSERT_SINGLE_1BIT_POS32
+#endif
+
 PERL_CALLCONV char*	Perl_skipspace_flags(pTHX_ char *s, U32 flags)
 			__attribute__warn_unused_result__;
 #define PERL_ARGS_ASSERT_SKIPSPACE_FLAGS	\

regcomp.c

@@ -19398,17 +19398,8 @@ S_optimize_regclass(pTHX_
             bool already_inverted;
             bool are_equivalent;
 
-            /* Compute which bit is set, which is the same thing as, e.g.,
-             * ANYOF_CNTRL.  From
-             * https://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
-             * */
-            static const int MultiplyDeBruijnBitPosition2[32] = {
-                0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
-                31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
-                };
 
-            namedclass = MultiplyDeBruijnBitPosition2[(posixl
-                                                      * 0x077CB531U) >> 27];
+            namedclass = single_1bit_pos32(posixl);
             classnum = namedclass_to_classnum(namedclass);
 
             /* The named classes are such that the inverted number is one