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| author | Karl Williamson <khw@cpan.org> | 2021-07-20 07:22:00 -0600 |
|---|---|---|
| committer | Karl Williamson <khw@cpan.org> | 2021-07-30 05:41:27 -0600 |
| commit | 995a49544ee5d0b46679907f5ba9fe50be890438 (patch) | |
| tree | e959e2c9eab948bb79a0fc8a676276ebf04b4c6b /perl.h | |
| parent | bf874180e9a7a8fbb74ab7eaa5c683ecc5a6ffc7 (diff) | |
| download | perl-995a49544ee5d0b46679907f5ba9fe50be890438.tar.gz | |
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.
Diffstat (limited to 'perl.h')
| -rw-r--r-- | perl.h | 12 |
1 files changed, 12 insertions, 0 deletions
@@ -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. |