28 lines
554 B
Go
28 lines
554 B
Go
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package bits
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// IntN returns the signed two's complement of x with the specified integer bit
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// width.
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//
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// Examples of unsigned (n-bit width) x values on the left and decoded values on
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// the right:
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//
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// 0b011 -> 3
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// 0b010 -> 2
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// 0b001 -> 1
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// 0b000 -> 0
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// 0b111 -> -1
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// 0b110 -> -2
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// 0b101 -> -3
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// 0b100 -> -4
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func IntN(x uint64, n uint) int64 {
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signBitMask := uint64(1 << (n - 1))
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if x&signBitMask == 0 {
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// positive.
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return int64(x)
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}
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// negative.
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v := int64(x ^ signBitMask) // clear sign bit.
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v -= int64(signBitMask)
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return v
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}
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