kdeng00
70 lines
1.8 KiB
C
70 lines
1.8 KiB
C
/*
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*
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* Exercise 2-7. Write a function invert(x,p,n) that returns x with the n bits that
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* begin at position p inverted (i.e., 1 changed into 0 and vice versa), leaving the
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* others unchanged.
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*
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* Author: Kun Deng
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*/
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#include <stdio.h>
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#include <stdlib.h>
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// Returns x with the n bits that begin at position p inverted
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// (i.e., 1 changed into 0 and vice versa), leaving the others unchanged.
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int invert(unsigned int x, int p, int n);
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int main(int argc, char **argv)
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{
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unsigned int x = 511;
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int p = 4;
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int n = 3;
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if (argc == 4)
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{
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x = atoi(argv[1]);
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p = atoi(argv[2]);
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n = atoi(argv[3]);
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}
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printf("Calling invert(%d, %d, %d)", x, p, n);
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printf(" = %d\n", invert(x, p, n));
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return 0;
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}
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int invert(unsigned int x, int p, int n)
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{
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int x_inverted = x;
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printf("%d ^ (~(~0 << %d) << (%d ", x, n, p);
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if (n == 1)
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{
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printf(" - 1))\n");
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printf("%d ^ (~(%d << %d) << (%d - 1))\n", x, ~(0), n, p);
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printf("%d ^ (~(%d) << (%d - 1))\n", x, (~(0) << n), p);
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printf("%d ^ (%d << (%d - 1))\n", x, ~(~(0) << n), p);
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printf("%d ^ (%d << %d)\n", x, ~(~(0) << n), (p - 1));
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printf("%d ^ %d\n", x, (~(~(0) << n) << (p - 1)));
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// No need to add 1 when the bit amount is 1 in (p + 1 - n)
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x_inverted = x ^ (~(~0U << n) << (p - 1));
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}
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else
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{
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printf(" + 1 - %d))\n", n);
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printf("%d ^ (~(%d << %d) << (%d + 1 - %d))\n", x, ~(0), n, p, n);
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printf("%d ^ (~(%d) << (%d + 1 - %d))\n", x, (~(0) << n), p, n);
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printf("%d ^ (%d << (%d + 1 - %d))\n", x, ~(~(0) << n), p, n);
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printf("%d ^ (%d << %d)\n", x, ~(~(0) << n), (p + 1 - n));
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printf("%d ^ %d\n", x, (~(~(0) << n) << (p + 1 - n)));
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x_inverted = x ^ (~(~0U << n) << (p + 1 - n));
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}
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return x_inverted;
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}
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