zqz/platform-external-webrtc
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Make energy calculation in AGC not overflow.

Browse Source 
An energy value is calculated by summing squares of processed audio
samples. The expression 'out*out >> 6' could overflow. In this CL we
change it to 'out*(out>>6) + out*(out*(out%(1<<6))>>6)'.

The which is verified and proven to be equal, but doesn't
overflow. The change also passes our change-detection tests in
GainControlBitExactnessTest.*

We verified with Godbolt that the modulo and divisions are converted
into branch-free bitwise operations.

NOTRY=True # changing comment, tests just passed.

Bug: chromium:780638, chromium:780376
Change-Id: I415535193433a2fbc275c643fb4e4026ba3e0bdd
Reviewed-on: https://webrtc-review.googlesource.com/20867
Commit-Queue: Alex Loiko <aleloi@webrtc.org>
Reviewed-by: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20589}
This commit is contained in:
Alex Loiko
2017-11-07 16:34:32 +01:00
committed by Commit Bot
parent fbb3b7d004
commit 7cfbf3a0ff
1 changed files with 6 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
modules/audio_processing/agc/legacy/digital_agc.c
View File

@ -607,7 +607,12 @@ int16_t WebRtcAgc_ProcessVad(AgcVad* state, // (i) VAD state
out = buf2[k] + HPstate;
tmp32 = 600 * out;
HPstate = (int16_t)((tmp32 >> 10) - buf2[k]);
nrg += (out * out) >> 6;
// Add 'out * out / 2**6' to 'nrg' in a non-overflowing
// way. Guaranteed to work as long as 'out * out / 2**6' fits in
// an int32_t.
nrg += out * (out / (1 << 6));
nrg += out * (out % (1 << 6)) / (1 << 6);
}
}
state->HPstate = HPstate;