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libosmo-netif
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amr: Clarify size of AMR BWE header and ToC 

Change-Id: I34c76b18ee45e12dba92864715e8ef91e6de3b01
This commit is contained in:
Pau Espin 2022-12-21 21:32:25 +01:00
parent 550aaa28dc
commit 99e5470ece
2 changed files with 8 additions and 4 deletions
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3
include/osmocom/netif/amr.h
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@ -43,6 +43,9 @@ struct amr_hdr_bwe {
uint8_t data[0];
} __attribute__((packed));
/* See diagram above: CMR (4) + F (1) + FT (4) + Q (1) = 10 */
#define AMR_HDR_BWE_LEN_BITS 10
/*
* 4.4. Octet-aligned Mode:
*

9
src/amr.c
View File

@ -188,7 +188,7 @@ int osmo_amr_oa_to_bwe(uint8_t *payload, unsigned int payload_len)
}
/* Calculate new payload length */
bwe_payload_len = (10 + osmo_amr_bits(ft) + 7) / 8;
bwe_payload_len = (AMR_HDR_BWE_LEN_BITS + osmo_amr_bits(ft) + 7) / 8;
return bwe_payload_len;
}
@ -266,7 +266,8 @@ int osmo_amr_bwe_to_iuup(uint8_t *payload, unsigned int payload_len)
amr_speech_len_bits = osmo_amr_bits(ft);
amr_speech_len_bytes = osmo_amr_bytes(ft);
required_len_bits = amr_speech_len_bits + 10; /* shift of 10 bits */
/* shift of AMR_HDR_BWE_LEN_BITS (10) bits, aka remove BWE Hdr + ToC: */
required_len_bits = AMR_HDR_BWE_LEN_BITS + amr_speech_len_bits;
if (payload_len < (required_len_bits + 7)/8)
return -1;
@ -288,7 +289,7 @@ int osmo_amr_bwe_to_iuup(uint8_t *payload, unsigned int payload_len)
int osmo_amr_iuup_to_bwe(uint8_t *payload, unsigned int payload_len,
unsigned int payload_maxlen)
{
/* shift all bits by 10 */
/* shift all bits by AMR_HDR_BWE_LEN_BITS (10) */
unsigned int i, required_len_bits, required_len_bytes;
int ft = osmo_amr_bytes_to_ft(payload_len);
@ -303,7 +304,7 @@ int osmo_amr_iuup_to_bwe(uint8_t *payload, unsigned int payload_len,
i = payload_len + 1;
payload[i] = (payload[i - 2] << 6);
for (i = payload_len; i >= 2; i--) {
/* we have to shift the payload by 10 bits to get only the Class A, B, C bits */
/* we have to shift the payload by AMR_HDR_BWE_LEN_BITS (10) bits to prepend BWE Hdr + ToC */
payload[i] = (payload[i - 1] >> 2) | (payload[i - 2] << 6);
}
payload[i] = (payload[i - 1] >> 2);