68 lines
1.4 KiB
C
68 lines
1.4 KiB
C
/**
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* :author: Dan Buch (daniel.buch@gmail.com)
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*/
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#include <stdio.h>
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static unsigned int mask[] = {
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0x55555555,
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0x33333333,
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0x0F0F0F0F,
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0x00FF00FF,
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0x0000FFFF
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};
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int get_bit_count(unsigned int x)
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{
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printf("get_bit_count(%d)\n", x);
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int i;
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int x_and_mask;
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int x_shifted;
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int x_shifted_and_mask;
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int shift; /* Number of positions to shift to right*/
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for (i = 0, shift = 1; i < 5; i++, shift *= 2) {
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printf(" START loop\n");
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printf(" i = %d, x = %d, shift = %d\n", i, x, shift);
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x_and_mask = x & mask[i];
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printf(" x & mask[i] = %d\n", x_and_mask);
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x_shifted = x >> shift;
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printf(" x >> shift = %d\n", x_shifted);
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x_shifted_and_mask = x_shifted & mask[i];
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printf(" (x >> shift) & mask[i] = %d\n", x_shifted_and_mask);
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x = x_and_mask + x_shifted_and_mask;
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printf(" x = %d\n", x);
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printf(" END loop\n");
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}
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return x;
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}
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int main()
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{
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int to_test[] = {0, 5, 7};
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int current;
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/*
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size_t mask_len = sizeof(mask) / sizeof(unsigned int);
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for (int i = 0; i < mask_len; i++) {
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printf("mask[%d] = %d\n", i, mask[i]);
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}
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*/
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for (int i = 0; i < 3 ; i++) {
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current = to_test[i];
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printf("get_bit_count(%d) -> %d\n", current, get_bit_count(current));
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}
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}
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/* vim:filetype=c:fileencoding=utf-8
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*/
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