Teledyne LeCroy Protocol Analyzers File-Based Decoding User Manual - Manual (Page 48)

Chapter 11: Primitives File-based Decoding User Manual
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LeCroy Corporation
PeekNBits()
PeekNBits(integer>)
Parameter Meaning
Default
Value Comments
bit_count integer
Support
Supported by all LeCroy analyzers.
Return value
None.
Comments
Reads bit_count bits from the data source. The difference between PeekNBits and
NextNBits is that PeekNBits does not advance the global bit offset. PeekNBits can
be used to make decisions about how to parse the next fields without affecting
subsequent calls to NextNBits. If PeekNBits is called without a prior call to
GetNBits, the result is undefined. Note that bits are indexed starting at bit 0.
Example
raw = 'F0F0';# 1111000011110000 binary
result1 = GetNBits ( raw, 2, 4 );
result2 = PeekNBits(5);
result3 = NextNBits(2);
This results in:
result1 == C
result2 == 7
result3 == 0
A call to GetNBits, starting at bit 2, reads 4 bits (1100), and returns the value 0xC.
A call to PeekNBits, starting at bit 6, reads 5 bits (00111), and returns the value 0x7.
A call to NextNBits, starting at bit 6, reads 2 bits (00), and returns the value 0x0.