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[2/2] bitvec: Add comment about bit ordering

Message ID 1450693588-21461-2-git-send-email-jerlbeck@sysmocom.de
State Accepted
Headers show

Commit Message

Jacob Erlbeck Dec. 21, 2015, 10:26 a.m. UTC 
The bitvec implementation expects an MSB first encoded bitstream,
which is not mentioned anywhere explicitly.

This commits adds a comment to the bitvec header file.

Sponsored-by: On-Waves ehf
---
 include/osmocom/core/bitvec.h | 8 ++++++++
 1 file changed, 8 insertions(+)
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Patch

diff --git a/include/osmocom/core/bitvec.h b/include/osmocom/core/bitvec.h
index 445730e..89eb784 100644
--- a/include/osmocom/core/bitvec.h
+++ b/include/osmocom/core/bitvec.h
@@ -28,6 +28,14 @@ 
 
 /*! \file bitvec.h
  *  \brief Osmocom bit vector abstraction
+ *
+ *  These functions assume a MSB (most significant bit) first layout of the
+ *  bits, so that for instance the 5 bit number abcde (a is MSB) can be
+ *  embedded into a byte sequence like in xxxxxxab cdexxxxx. The bit count
+ *  starts with the MSB, so the bits in a byte are numbered (MSB) 01234567 (LSB).
+ *  Note that there are other incompatible encodings, like it is used
+ *  for the EGPRS RLC data block headers (there the bits are numbered from LSB
+ *  to MSB).
  */
 
 #include <stdint.h>