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[188.192.139.191]) by smtp.gmail.com with ESMTPSA id l3sm45002633wrt.29.2020.01.20.11.20.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jan 2020 11:20:51 -0800 (PST) From: Andreas Rheinhardt To: ffmpeg-devel@ffmpeg.org Date: Mon, 20 Jan 2020 20:20:42 +0100 Message-Id: <20200120192043.4288-1-andreas.rheinhardt@gmail.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH 1/2] avcodec/adxenc: Avoid undefined left shift of negative numbers X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Cc: Andreas Rheinhardt Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Replace "((a << shift) + b) >> shift" by "a + (b >> shift)". This avoids a left shift which also happens to trigger undefined behaviour in case "a" is negative. This affected the FATE-tests acodec-adpcm-adx and acodec-adpcm-adx-trellis; it also fixes ticket #8008. Signed-off-by: Andreas Rheinhardt --- The equivalence of the old code and the new code in the first two changes is clear from the type of wav[i] (int16_t) and the fact that COEFF_BITS is 12 (i.e. no high bits are lost when left shifting); for the last change the equivalence depends upon scale being representable in an uint16_t. I don't know whether this is indeed so (the direct estimate gives an upper bound of (2^19 + 2^15 + 1) / 7), but it better should be so because scale is written via AV_WB16. Maybe it should be clipped if it is outside of this range? libavcodec/adxenc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/libavcodec/adxenc.c b/libavcodec/adxenc.c index a781151b44..93b902b0e1 100644 --- a/libavcodec/adxenc.c +++ b/libavcodec/adxenc.c @@ -48,7 +48,7 @@ static void adx_encode(ADXContext *c, uint8_t *adx, const int16_t *wav, s2 = prev->s2; for (i = 0, j = 0; j < 32; i += channels, j++) { s0 = wav[i]; - d = ((s0 << COEFF_BITS) - c->coeff[0] * s1 - c->coeff[1] * s2) >> COEFF_BITS; + d = s0 + ((-c->coeff[0] * s1 - c->coeff[1] * s2) >> COEFF_BITS); if (max < d) max = d; if (min > d) @@ -79,13 +79,13 @@ static void adx_encode(ADXContext *c, uint8_t *adx, const int16_t *wav, s1 = prev->s1; s2 = prev->s2; for (i = 0, j = 0; j < 32; i += channels, j++) { - d = ((wav[i] << COEFF_BITS) - c->coeff[0] * s1 - c->coeff[1] * s2) >> COEFF_BITS; + d = wav[i] + ((-c->coeff[0] * s1 - c->coeff[1] * s2) >> COEFF_BITS); d = av_clip_intp2(ROUNDED_DIV(d, scale), 3); put_sbits(&pb, 4, d); - s0 = ((d << COEFF_BITS) * scale + c->coeff[0] * s1 + c->coeff[1] * s2) >> COEFF_BITS; + s0 = d * scale + ((c->coeff[0] * s1 + c->coeff[1] * s2) >> COEFF_BITS); s2 = s1; s1 = s0; }