From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id 723404792B for ; Wed, 27 Sep 2023 13:56:29 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id B5E3668CAF9; Wed, 27 Sep 2023 16:56:27 +0300 (EEST) Received: from haasn.dev (haasn.dev [78.46.187.166]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id AF4B168CA16 for ; Wed, 27 Sep 2023 16:56:21 +0300 (EEST) Received: from haasn.dev (unknown [10.30.0.2]) by haasn.dev (Postfix) with ESMTP id 35AED41827; Wed, 27 Sep 2023 15:56:21 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=haasn.xyz; s=mail; t=1695822981; bh=yOI/b5jsHtfL6Sxn9PKrsmX/nsGdX6bhq36n5zNaLuc=; h=From:To:Cc:Subject:Date:From; b=kDAAVgiVIqKLEnmY7wK9rq3YqJcEFihgAK8d1kS9irfZS2+kr4bhhJDimsJVmhKN7 pX0b+jglXc6ZrW/zVpQIwTCwQKA96YgfjRf+Asxoa4cQHQ9WTtex+eOhYceBRuhZBg HrI13m/5r1JeQb8fxTGgvx47fmdigxUhIDXVTNb8= From: Niklas Haas To: ffmpeg-devel@ffmpeg.org Date: Wed, 27 Sep 2023 15:56:15 +0200 Message-ID: <20230927135617.33952-1-ffmpeg@haasn.xyz> X-Mailer: git-send-email 2.42.0 MIME-Version: 1.0 Subject: [FFmpeg-devel] [PATCH 1/3] lavc/h274: fix PRNG definition X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 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: Niklas Haas Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: From: Niklas Haas The spec specifies x^31 + x^3 + 1 as the polynomial, but the diagram in Figure 1-1 omits the +1 offset. The initial implementation was based on the diagram, but this is wrong (produces subtly incorrect results). --- libavcodec/h274.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libavcodec/h274.c b/libavcodec/h274.c index a69f9411429..fc111cdb50d 100644 --- a/libavcodec/h274.c +++ b/libavcodec/h274.c @@ -38,7 +38,7 @@ static void prng_shift(uint32_t *state) { // Primitive polynomial x^31 + x^3 + 1 (modulo 2) uint32_t x = *state; - uint8_t feedback = (x >> 2) ^ (x >> 30); + uint8_t feedback = 1u ^ (x >> 2) ^ (x >> 30); *state = (x << 1) | (feedback & 1u); } -- 2.42.0 _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".