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NGAP: Correct encoding of AMF Set ID and Pointer

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Taking the example of the AMF Set ID, the previous version of the macro
used another macro to encode the number, then marked the last 6 bits in
the bit string (of length 16/2 bytes) as unused. This is wrong, because,
assuming AMF Set ID=3, it basically truncates the number by encoding all
16 bits and cutting off the last 6, like this:

  ------------------- encode 16 bits
  0000 0000 0000 0011
  ------------        take these 10 bits

So what remains is these bit positions of the number:
(16,15,14,13,12,11,10,9,8,7) -- the last 6 bits are cut (and the first 6
are either 0 or garbage, because they don't exist).

Instead, manually encode bits (10,9,8,7,6,5,4,3) in the first byte, and
(2,1) in the second byte of the bit string, like so:

  ------------        encode 10 bits
  0000 0000 1100 0000
  ------------        take these 10 bits

Do the same with the pointer.

The AMF Region ID above is correct, as it is exactly 8 bits.
This commit is contained in:
Robert Schmidt
2024-05-06 12:03:20 +02:00
parent 8d225a7e10
commit 0fb0b055e5
1 changed files with 15 additions and 11 deletions
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openair3/UTILS/conversions.h
+15 -11
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@@ -190,18 +190,22 @@ do { \
(aSN)->bits_unused = 0; \
} while(0)
#define AMF_SETID_TO_BIT_STRING(x, aSN) \
do { \
INT16_TO_OCTET_STRING(x, aSN); \
(aSN)->bits_unused = 6; \
} while(0)
#define AMF_POINTER_TO_BIT_STRING(x, aSN) \
do { \
INT8_TO_OCTET_STRING(x, aSN); \
(aSN)->bits_unused = 2; \
} while(0)
#define AMF_SETID_TO_BIT_STRING(x, aSN) \
do { \
(aSN)->buf = calloc(2, sizeof(uint8_t)); \
(aSN)->buf[0] = ((x) >> 2) & 0xff; \
(aSN)->buf[1] = ((x) & 0x03) << 6; \
(aSN)->size = 2; \
(aSN)->bits_unused = 6; \
} while (0)
#define AMF_POINTER_TO_BIT_STRING(x, aSN) \
do { \
(aSN)->buf = calloc(1, sizeof(uint8_t)); \
(aSN)->buf[0] = ((x) & 0x3f) << 2; \
(aSN)->size = 1; \
(aSN)->bits_unused = 2; \
} while (0)
#define ENCRALG_TO_BIT_STRING(encralg, bitstring) \
do { \