Author: Dann Corbit
Date: 22:25:46 01/04/99
Go up one level in this thread
I would be curious to see timings of the assembly language variants versus this
simple C doo-dad:
#include <limits.h>
#include <stdlib.h>
#if CHAR_BIT == 8
static const char bits[256] =
{
0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7,
4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8
};
#else
PLEASE FIX ME.
#endif
/*
** Count bits in each byte
**
** by Auke Reitsma
**
** Torqued by D. Corbit
** This version makes no assumptions about integer size.
** If CHAR_BIT is not equal to 8, you will have to provide
** a corrected table (see above).
*/
int bit_count_bytes(unsigned long x)
{
unsigned char * Ptr = (unsigned char *) &x;
int Accu;
switch (sizeof(x))
{
case 4:
Accu = bits[Ptr[0]] + bits[Ptr[1]] + bits[Ptr[2]] + bits[Ptr[3]];
break;
case 8:
Accu = bits[Ptr[0]] + bits[Ptr[1]] + bits[Ptr[2]] + bits[Ptr[3]] +
bits[Ptr[4]] + bits[Ptr[5]] + bits[Ptr[6]] + bits[Ptr[7]];
break;
default:
{
size_t i;
Accu = 0;
for (i = 0; i < sizeof(int); i++)
Accu += bits[Ptr[i]];
}
}
return Accu;
}
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