Bit extract. Extracts a range of bits from an expression.
Syntax |
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bitx (source position length)
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Formal Declaration |
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bitx:any (source:any position:s16 length:u16)
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Parameters |
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- source
The value from which to extract a range of bits. Its type is restricted to the INT and PTR classes.
- position
This parameter specifies the starting bit position (positive
value), or the ending bit position (negative value) of the extraction.
Regardless of the size of the source value, bit positions are always
numbered from left to right. The leftmost bit of the source is bit 0.
- length
The number of bits to extract. This value may not exceed 64.
This function is sensitive to the type of the source parameter. If a S32 or
U32 value is passed, the format of the word (start/end positions) is as
follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------------------------------------------------------+
| |
+---------------------------------------------------------------+
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If a S16 or U16 value is passed, the format of the word (start/end positions)
is as follows:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-------------------------------+
| |
+-------------------------------+
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Examples |
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This is a 32-bit word containing the bit pattern
for the hex value 4015381c:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------------------------------------------------------+
|0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 1 1 0 0 0 0 0 0 1 1 1 0 0|
+---------------------------------------------------------------+
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$nmdebug > var xx:u32 4015381c
$nmdebug > wl bitx(xx,#10,5)
$a
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Extract five bits starting at position 10 (this yields the bit pattern 01010).
$nmdebug > wl bitx(xx,-#14,5)
$a
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Extract five bits ending at position 14 (this yields the bit pattern 01010).
This is the same field of bits as in the previous example.
Limitations, Restrictions |
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If an extended address source is passed, the extraction location must fall
entirely within the 64-bit offset part. Since EADDR types have a total
of 96 bits, the valid bit positions are 32 through 95.
