Add 64bit single-1bit_pos()

This will prove useful in future commits on platforms that have 64 bit
capability.

The deBruijn sequence used here, taken from the internet, differs
from the 32 bit one in how they treat a word with no set bits.  But this
is considered undefined behavior, so that difference is immaterial.

Apparently figuring this out uses brute force methods, and so I decided
to live with this difference, rather than to expend the time needed to
bring them into sync.

embed.fnc

@@ -1142,6 +1142,9 @@ 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
+#ifdef HAS_QUAD
+CTiRp	|unsigned|single_1bit_pos64|U64 word
+#endif
 #ifndef EBCDIC
 CTiRp	|unsigned int|variant_byte_number|PERL_UINTMAX_T word
 #endif

embed.h

@@ -835,6 +835,9 @@
 #define pad_setsv(a,b)		Perl_pad_setsv(aTHX_ a,b)
 #define pad_sv(a)		Perl_pad_sv(aTHX_ a)
 #endif
+#if defined(HAS_QUAD)
+#define single_1bit_pos64	Perl_single_1bit_pos64
+#endif
 #if defined(HAVE_INTERP_INTERN)
 #define sys_intern_clear()	Perl_sys_intern_clear(aTHX)
 #define sys_intern_init()	Perl_sys_intern_init(aTHX)

globvar.sym

@@ -13,6 +13,7 @@ PL_charclass
 PL_check
 PL_core_reg_engine
 PL_deBruijn_bitpos_tab32
+PL_deBruijn_bitpos_tab64
 PL_EXACTFish_bitmask
 PL_EXACT_REQ8_bitmask
 PL_extended_utf8_dfa_tab

inline.h

@@ -664,6 +664,27 @@ Perl_is_utf8_invariant_string_loc(const U8* const s, STRLEN len, const U8 ** ep)
     return TRUE;
 }
 
+#ifdef HAS_QUAD
+
+PERL_STATIC_INLINE unsigned
+Perl_single_1bit_pos64(U64 word)
+{
+    /* Given a 64-bit word known to contain all zero bits except one 1 bit,
+     * find and return the 1's position: 0..63 */
+
+#  ifdef PERL_CORE    /* macro not exported */
+    ASSUME(isPOWER_OF_2(word));
+#  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_tab64[(word * PERL_deBruijnMagic64_)
+                                                    >> PERL_deBruijnShift64_];
+}
+
+#endif
+
 PERL_STATIC_INLINE unsigned
 Perl_single_1bit_pos32(U32 word)
 {
@@ -674,9 +695,6 @@ Perl_single_1bit_pos32(U32 word)
     ASSUME(isPOWER_OF_2(word));
 #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_];
 }

perl.h

@@ -5849,6 +5849,15 @@ PL_deBruijn_bitpos_tab32[] = {
     31, 27, 13, 23, 21, 19, 16,  7, 26, 12, 18,  6, 11,  5, 10,  9
 };
 
+EXTCONST U8
+PL_deBruijn_bitpos_tab64[] = {
+    /* https://stackoverflow.com/questions/11376288/fast-computing-of-log2-for-64-bit-integers */
+    63,  0, 58,  1, 59, 47, 53,  2, 60, 39, 48, 27, 54, 33, 42,  3,
+    61, 51, 37, 40, 49, 18, 28, 20, 55, 30, 34, 11, 43, 14, 22,  4,
+    62, 57, 46, 52, 38, 26, 32, 41, 50, 36, 17, 19, 29, 10, 13, 21,
+    56, 45, 25, 31, 35, 16,  9, 12, 44, 24, 15,  8, 23,  7,  6,  5
+};
+
 #else
 
 EXTCONST bool PL_valid_types_IVX[];
@@ -5858,12 +5867,15 @@ 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[];
+EXTCONST U8   PL_deBruijn_bitpos_tab64[];
 
 #endif
 
 /* The constants for using PL_deBruijn_bitpos_tab */
 #define PERL_deBruijnMagic32_  0x077CB531
 #define PERL_deBruijnShift32_  27
+#define PERL_deBruijnMagic64_  0x07EDD5E59A4E28C2
+#define PERL_deBruijnShift64_  58
 
 /* In C99 we could use designated (named field) union initializers.
  * In C89 we need to initialize the member declared first.

proto.h

@@ -4732,6 +4732,14 @@ PERL_CALLCONV int	Perl_PerlProc_pipe_cloexec(pTHX_ int *pipefd)
 #define PERL_ARGS_ASSERT_PERLPROC_PIPE_CLOEXEC	\
 	assert(pipefd)
 
+#endif
+#if defined(HAS_QUAD)
+#ifndef PERL_NO_INLINE_FUNCTIONS
+PERL_STATIC_INLINE unsigned	Perl_single_1bit_pos64(U64 word)
+			__attribute__warn_unused_result__;
+#define PERL_ARGS_ASSERT_SINGLE_1BIT_POS64
+#endif
+
 #endif
 #if defined(HAS_SOCKET)
 PERL_CALLCONV int	Perl_PerlSock_accept_cloexec(pTHX_ int listenfd, struct sockaddr *addr, Sock_size_t *addrlen)