libosmocodec: osmo_hr_check_sid(): simplify the logic

According to TS 101 318, section 5.2.2, a SID frame is identified
by a SID codeword consisting of 79 bits (r34..r112) which are all 1.
Given that there are no gaps in the codeword, we don't really need
to use bitvec_get_bit_pos() and check each field individually.
This brings additional complexity and negatively affects performance.

Instead, let's use bitvec_get_bit_pos() to check all bits in a row.

Change-Id: I678f8ff92317fe87f1aca511a3a062ad898e55cc
Related: SYS#5853
changes/31/27431/1
Vadim Yanitskiy 9 months ago
parent b54229d2ec
commit 7ec19de720
  1. 22
      src/codec/gsm620.c

@ -264,12 +264,6 @@ const uint16_t gsm620_voiced_bitorder[112] = {
81, /* Code 3:7 */
};
static inline uint16_t mask(const uint8_t msb)
{
const uint16_t m = (uint16_t)1 << (msb - 1);
return (m - 1) ^ m;
}
/*! Check whether RTP frame contains HR SID code word according to
* TS 101 318 §5.2.2
* \param[in] rtp_payload Buffer with RTP payload
@ -278,15 +272,15 @@ static inline uint16_t mask(const uint8_t msb)
*/
bool osmo_hr_check_sid(const uint8_t *rtp_payload, size_t payload_len)
{
uint8_t i, bits[] = { 1, 2, 8, 9, 5, 4, 9, 5, 4, 9, 5, 4, 9, 5 };
struct bitvec bv;
bv.data = (uint8_t *) rtp_payload;
bv.data_len = payload_len;
bv.cur_bit = 33;
struct bitvec bv = {
.data = (uint8_t *)rtp_payload,
.data_len = payload_len,
};
/* code word is all 1 at given bits, numbered from 1, MODE is always 3 */
for (i = 0; i < ARRAY_SIZE(bits); i++)
if (bitvec_get_uint(&bv, bits[i]) != mask(bits[i]))
/* A SID frame is identified by a SID codeword consisting of 79 bits which are all 1,
* so we basically check if all bits in range r34..r112 (inclusive) are 1. */
for (bv.cur_bit = 33; bv.cur_bit < bv.data_len * 8; bv.cur_bit++)
if (bitvec_get_bit_pos(&bv, bv.cur_bit) != ONE)
return false;
return true;

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