Hi Takashi, Clemens, all,
Takashi Iwai wrote:
Benoît Thébaudeau wrote:
Clemens Ladisch wrote:
I'll see if I can cobble together some TLV checking code ...
Great.
Because it's useless to wait until the end of the loop to return -EINVAL,
It is not necessary to optimize for error cases.
It's not an optimization, but a simplification. Otherwise, pos would have to be tested again after the loop to differentiate the loop-skipped case from the at-least-one-loop-iteration cases to return either -EINVAL or the prev submax.
Unless it's really a hot path, such a micro-optimization doesn't give much value.
Rather better to keep the standard style that makes people easier to read the code. A do-while loop with a large block is usually less readable than a normal while loop.
Would you agree with the following revision?
[PATCH] alsa-lib/tlv: improve robustness of raw value ranges
snd_tlv_convert_from_dB() relies on rangemin/max blindly. Since this function is exported, it is better for robustness and consistency to parse the range properly, which this patch does.
Signed-off-by: Benoît Thébaudeau benoit.thebaudeau@advansee.com
--- alsa-lib/src/control/tlv.c +++ alsa-lib/src/control/tlv.c @@ -291,41 +291,37 @@ int snd_tlv_convert_from_dB(unsigned int { switch (tlv[0]) { case SND_CTL_TLVT_DB_RANGE: { - long dbmin, dbmax, prev_rangemax; + long dbmin, dbmax, prev_submax; unsigned int pos, len; len = int_index(tlv[1]); - if (len > MAX_TLV_RANGE_SIZE) - return -EINVAL; - if (snd_tlv_get_dB_range(tlv, rangemin, rangemax, - &dbmin, &dbmax)) + if (len < 6 || len > MAX_TLV_RANGE_SIZE) return -EINVAL; - if (db_gain <= dbmin) { - *value = rangemin; - return 0; - } else if (db_gain >= dbmax) { - *value = rangemax; - return 0; - } pos = 2; - prev_rangemax = 0; + prev_submax = 0; while (pos + 4 <= len) { - rangemin = (int)tlv[pos]; - rangemax = (int)tlv[pos + 1]; + long submin, submax; + submin = (int)tlv[pos]; + submax = (int)tlv[pos + 1]; + if (rangemax < submax) + submax = rangemax; if (!snd_tlv_get_dB_range(tlv + pos + 2, - rangemin, rangemax, + submin, submax, &dbmin, &dbmax) && db_gain >= dbmin && db_gain <= dbmax) return snd_tlv_convert_from_dB(tlv + pos + 2, - rangemin, rangemax, + submin, submax, db_gain, value, xdir); else if (db_gain < dbmin) { - *value = xdir ? rangemin : prev_rangemax; + *value = xdir || pos == 2 ? submin : prev_submax; return 0; } - prev_rangemax = rangemax; + prev_submax = submax; + if (rangemax == submax) + break; pos += int_index(tlv[pos + 3]) + 4; } - return -EINVAL; + *value = prev_submax; + return 0; } case SND_CTL_TLVT_DB_SCALE: { int min, step, max;