falconia has uploaded this change for review. ( https://gerrit.osmocom.org/c/libosmocore/+/37227?usp=email )

Change subject: codec: make osmo_hr_check_sid() more efficient ......................................................................

codec: make osmo_hr_check_sid() more efficient

The operation of checking an HRv1 codec frame for the possibility of a perfect, error-free SID entails checking the last 79 bits out of 112, to see if they are all 1s. This operation can be done much more efficiently without using bitvec.

Change-Id: Ib14204102c03c14d6c5aab42b0ffbef2c3dda3fd --- M src/codec/gsm620.c 1 file changed, 35 insertions(+), 12 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/27/37227/1

diff --git a/src/codec/gsm620.c b/src/codec/gsm620.c index ef1d3b9..0489748 100644 --- a/src/codec/gsm620.c +++ b/src/codec/gsm620.c @@ -23,8 +23,6 @@ #include <stdbool.h> #include <string.h>

-#include <osmocom/core/bitvec.h> -#include <osmocom/core/utils.h> #include <osmocom/codec/codec.h>

/* GSM HR unvoiced (mode=0) frames - subjective importance bit ordering */ @@ -270,21 +268,32 @@ * \param[in] rtp_payload Buffer with RTP payload * \param[in] payload_len Length of payload * \returns true if code word is found, false otherwise + * + * Note that this function checks only for a perfect, error-free SID. + * Unlike GSM 06.31 for FR or GSM 06.81 for EFR, GSM 06.41 spec for HR + * does not prescribe exact bit counting rules, hence detection of + * partially corrupted SID frames in downstream network elements + * without out-of-band indication is not possible. */ bool osmo_hr_check_sid(const uint8_t *rtp_payload, size_t payload_len) { - struct bitvec bv = { - .data = (uint8_t *)rtp_payload, - .data_len = payload_len, - }; + static const uint8_t all_ff_bytes[9] = + {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};

- /* 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; + if (payload_len < GSM_HR_BYTES) + return false;

- return true; + /* 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. However, given the position of + * these bits in the frame, the most efficient way to perform + * this check does not use any bit-level operations. */ + if ((rtp_payload[4] & 0x7F) != 0x7F) + return false; + if (memcmp(rtp_payload + 5, all_ff_bytes, 9) == 0) + return true; + else + return false; }

/*! Reset the SID field of a potentially corrupted, but still valid GSM-HR