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Bits[GetBits] - extract specified bits from a number
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Calling Sequence
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GetBits(number, locns)
GetBits(number, locns, options)
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Parameters
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number
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an integer
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locns
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a single or sequence of locations or ranges
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options
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-
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optional arguments
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Description
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The GetBits command extracts the specified bits from a number. The locns argument can be a sequence of bit locations or bit location ranges, including negative ranges and negative offsets. Note that all bit locations are given with 0 as the location of the least significant bit. For example, -1..0 can be used to extract the bits in a number in reverse order.
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The optional arguments for GetBits are as follows:
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output=form: where form can be sequence (the default), or number. When form is specified as sequence, the output will be in the form of a sequence of 0's and 1's corresponding to the specified bit locations. When form is specified as number, the bit sequence will be used to construct a number, where the first bit in locns will be the least significant bit in the output number.
bits=count: specifies the number of bits in the input number. Any bit references that exceed this value will have a value of zero. Any negative bit references that go past the least significant bit will return an error. The default bits value can be set via Settings.
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Examples
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![num := Join([1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1])](/support/helpjp/helpview.aspx?si=9312/file01174/math117.png)
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Get least significant bit.
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Get most significant bit. (This will be 1 if bits is not specified.)
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Get most significant bit assuming input is 16 bits
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Extract all bits - this is the same as Split
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![[GetBits(num, 0 .. -1)]](/support/helpjp/helpview.aspx?si=9312/file01174/math156.png)
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![[1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1]](/support/helpjp/helpview.aspx?si=9312/file01174/math159.png)
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![[1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 1, 1, 1]](/support/helpjp/helpview.aspx?si=9312/file01174/math166.png)
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Reverse order of the bits as a 16 bit number
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![[GetBits(num, -1 .. 0, bits = 16)]](/support/helpjp/helpview.aspx?si=9312/file01174/math172.png)
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![[0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 1]](/support/helpjp/helpview.aspx?si=9312/file01174/math175.png)
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Reverse order as a 16 bit number with number output is equivalent to extracting in reverse above followed by join
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| (8) |
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![Join([GetBits(num, -1 .. 0, bits = 16)])](/support/helpjp/helpview.aspx?si=9312/file01174/math188.png)
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| (9) |
Exchange first 8 bits and last 8 bits in a 16 bit number
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Check:
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