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refactor setbits #11

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refactor setbits #11

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4f4d6bb
Change meaning of `p` argument
isidroas Feb 16, 2025
5a98acf
refactor setbits()
isidroas Jan 20, 2025
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refactor setbits()
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@isidroas
isidroas committed Feb 16, 2025
commit 5a98acf3d242c9058df56345dddb24054f977df6
18 changes: 16 additions & 2 deletions chapter-2-types-operators-expressions/11.setbits.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,9 +16,23 @@ main()

int setbits(int x, int p, int n, int y)
{
x = x & (~((~(~0 << n)) << (p - n + 1)));
y = (y & (~(~0 << n))) << (p - n + 1);
/* xxx............xxx x */
/* yyy...........ynnn y */

/* least significant position of the bits touched */
int r = p - n + 1;

/* 000...011110...000 mask */
/* p r ...210 position */
int mask = ~(~0 << p + 1) & (~0 << r);

/* 000...0nnnn0...000 */
y = (y << r) & mask;

/* xxx...x0000x...xxx */
x = x & ~mask;

/* xxx...xnnnnx...xxx */
return x | y;
}