PERFORCE change 38065 for review
Peter Wemm
peter at FreeBSD.org
Sun Sep 14 17:02:37 PDT 2003
http://perforce.freebsd.org/chv.cgi?CH=38065
Change 38065 by peter at peter_work on 2003/09/14 17:01:54
Update the popcnt() stuff
Affected files ...
.. //depot/projects/hammer/sys/i386/i386/mp_machdep.c#13 edit
Differences ...
==== //depot/projects/hammer/sys/i386/i386/mp_machdep.c#13 (text+ko) ====
@@ -2437,6 +2437,12 @@
* -mcpu=pentiumpro and -march=pentiumpro then gcc-3.1 will use
* an imull, and in that case it is faster. In most other cases
* it appears slightly slower.
+ *
+ * Another variant (also from fortune):
+ * #define BITCOUNT(x) (((BX_(x)+(BX_(x)>>4)) & 0x0F0F0F0F) % 255)
+ * #define BX_(x) ((x) - (((x)>>1)&0x77777777) \
+ * - (((x)>>2)&0x33333333) \
+ * - (((x)>>3)&0x11111111))
*/
static __inline u_int32_t
popcnt(u_int32_t m)
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