Set/Unset Bits Operation

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O.B. - 06 Jul 2007 17:07 GMT

I've written a small operation that sets/unsets bits within an
unsigned integer. Is there a better way to do this?

static uint setBits(uint original, uint newValue, uint offset, unint
mask)
{
return ((original >> offset) & (~mask) | newValue) << offset;
}

Example:

uint test = 0xEC; // 1110 1100
uint TwoBitMask = 0x03;

uint offset = 3;

// Expect 1110 0100
uint result = setBits(test, 0, offset, TwoBitMask);

// Expect 1111 1100
result = setBits(test, 3, offset, TwoBitMask);

// Expect 1111 0100
result = setBits(test, 2, offset, TwoBitMask);

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O.B. - 06 Jul 2007 17:23 GMT

Small bug in that last one (bits dropped when shifted). Let's try
that again:

static uint setBits(uint original, uint newValue, uint offset, uint
mask)
{
return original & ~(mask << offset) | (newValue << offset);
}

> I've written a small operation that sets/unsets bits within an
> unsigned integer. Is there a better way to do this?
[quoted text clipped - 21 lines]
> // Expect 1111 0100
> result = setBits(test, 2, offset, TwoBitMask);

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Göran Andersson - 06 Jul 2007 20:17 GMT

> Small bug in that last one (bits dropped when shifted). Let's try
> that again:
[quoted text clipped - 4 lines]
> return original & ~(mask << offset) | (newValue << offset);
> }

I was just thinking when reading the first post that you should shift
the mask and the value instead of shifting the original. :)

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Göran Andersson
_____
http://www.guffa.com

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Set/Unset Bits Operation

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