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| author | Alan Coopersmith <alan.coopersmith@oracle.com> | 2016-02-25 23:36:50 -0800 |
|---|---|---|
| committer | Alan Coopersmith <alan.coopersmith@oracle.com> | 2016-03-03 18:24:12 -0800 |
| commit | 490a25e6f8a4d2482af4364c700b68ad11a4d10b (patch) | |
| tree | 87cb9f917700aa3dbcc57bfcce012473257b1491 /src/XSecurity.c | |
| parent | 54ba591149f3a92c5a4a66e428ae2a33d1027053 (diff) | |
| download | xorg-lib-libXext-490a25e6f8a4d2482af4364c700b68ad11a4d10b.tar.gz | |
Use __builtin_popcountl if available to replace Ones() in XSecurity.c
If the compiler knows of a better algorithm for counting the number of
bits set in a word for the target CPU, let it use that, instead of the
classic algorithm optimized for PDP-6.
Tested for the range of values used in XSecurity.c and verified results
are the same from both:
for (unsigned long i = 0; i <= XSecurityAllAuthorizationAttributes; i++) {
printf("ones: %d\tpopcnt: %d\n", Ones(i), __builtin_popcountl(i));
}
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Diffstat (limited to 'src/XSecurity.c')
| -rw-r--r-- | src/XSecurity.c | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/src/XSecurity.c b/src/XSecurity.c index 3ca75b1..56b37fc 100644 --- a/src/XSecurity.c +++ b/src/XSecurity.c @@ -196,15 +196,24 @@ XSecurityFreeXauth(Xauth *auth) XFree(auth); } -static int +#ifdef HAVE___BUILTIN_POPCOUNTL +# define Ones __builtin_popcountl +#else +/* + * Count the number of bits set to 1 in a 32-bit word. + * Algorithm from MIT AI Lab Memo 239: "HAKMEM", ITEM 169. + * http://dspace.mit.edu/handle/1721.1/6086 + */ +static inline int Ones(Mask mask) { register Mask y; - y = (mask >> 1) &033333333333; + y = (mask >> 1) & 033333333333; y = mask - y - ((y >>1) & 033333333333); return (((y + (y >> 3)) & 030707070707) % 077); } +#endif Xauth * XSecurityGenerateAuthorization( |