On Sat, 5 Mar 2016 19:03:24 +0100, Bart (bartjun...@gmail.com) wrote
about "[fpc-pascal] Bitcounting" (in
<camye31xhge_egouaqk7hegk7by0steko5en11dkg3dmjyxd...@mail.gmail.com>):
> Does FreePascal have a routine for counting bits?
[snip]
> Surely this can be done better?
If you don't mind a bit of C, attached is what I use. It is blazingly
fast compared to examining each bit.
It uses ASCIIZ strings, but can easily be converted to Pascal and
AnsiStrings (or whatever). However, I'll leave that to you.
--
Regards,
Dave [RLU #314465]
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
david.w.n...@googlemail.com (David W Noon)
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
#ifndef BIT_COUNT_H_INCLUDED
#define BIT_COUNT_H_INCLUDED
/* Functions to count how many 1-bits or 0-bits are in a buffer area.
*
* Copyright (C) 2015, David W. Noon. All rights reserved.
* This code is released under the Berkeley License.
*
*/
#ifdef __cplusplus
#include <cstdlib>
#include <cstdint> /* Requires C++11 or later. */
#else
#include <stdlib.h>
#include <stdint.h> /* Requires C99 or later. */
#endif
/* Function to count the number of 1 bits in a buffer. */
static uint32_t count_ones(const void * buffer, size_t bytes_count)
{
static const uint8_t ONES[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 };
uint32_t result = 0U;
#ifdef __cplusplus
const uint8_t * byte_ptr = reinterpret_cast<const uint8_t *>(buffer);
#else
const uint8_t * byte_ptr = (const uint8_t *) buffer;
#endif
for (size_t ctr = bytes_count; ctr > 0; --ctr)
{
result += ONES[*byte_ptr];
++byte_ptr;
}
return result;
}
/* Function to count the number of 0 bits in a buffer. */
static uint32_t count_zeroes(const void * buffer, size_t bytes_count)
{
static const uint8_t ZEROES[256] = {
8, 7, 7, 6, 7, 6, 6, 5, 7, 6, 6, 5, 6, 5, 5, 4,
7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3,
7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1,
7, 6, 6, 5, 6, 5, 5, 4, 6, 5, 5, 4, 5, 4, 4, 3,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1,
6, 5, 5, 4, 5, 4, 4, 3, 5, 4, 4, 3, 4, 3, 3, 2,
5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1,
5, 4, 4, 3, 4, 3, 3, 2, 4, 3, 3, 2, 3, 2, 2, 1,
4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0 };
uint32_t result = 0U;
#ifdef __cplusplus
const uint8_t * byte_ptr = reinterpret_cast<const uint8_t *>(buffer);
#else
const uint8_t * byte_ptr = (const uint8_t *) buffer;
#endif
for (size_t ctr = bytes_count; ctr > 0; --ctr)
{
result += ZEROES[*byte_ptr];
++byte_ptr;
}
return result;
}
#endif /* BIT_COUNT_H_INCLUDED */
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