From patchwork Mon Aug 6 18:14:51 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Fuerst X-Patchwork-Id: 1280691 Return-Path: X-Original-To: patchwork-dri-devel@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by patchwork2.kernel.org (Postfix) with ESMTP id 7F3BFDF288 for ; Mon, 6 Aug 2012 18:19:58 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 4E01AA090F for ; Mon, 6 Aug 2012 11:19:58 -0700 (PDT) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail-ob0-f177.google.com (mail-ob0-f177.google.com [209.85.214.177]) by gabe.freedesktop.org (Postfix) with ESMTP id 9E4569FD66 for ; Mon, 6 Aug 2012 11:14:51 -0700 (PDT) Received: by obbta17 with SMTP id ta17so6576390obb.36 for ; Mon, 06 Aug 2012 11:14:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:date:message-id:subject:from:to:cc:content-type; bh=VZ/GOW7ZMKH7Yt6LSq/2fgPIam2zafU+cnVPEz4bzjo=; b=g9+1SSU47D1OyPN8JLdTdFTSMImb61unTDVwHwDiC8bSozSK+GXgXe9C6aaCnmeeq0 tlbhAxXJpY7+N2iglu3u7hxWnMVrj8jB5RCEJCEbzp4NUC6YO7T/AEXnv5ua4gJYdP45 dRdtvErwPnN8BPDH2QUi2W8YDdKvprcIxZ3z6qyBQMrG+6UvBWkJ4nDGqj3Z6KUFBJV9 6AKg0uO6d8XtODy+ylp/C7R/zGScGqWa5e5ROdR7bXeX8o+Qe+rufQMzAnH/H1McUC0p 3NJdLifX8xdpQV551i4TVFWezMBzrfRL89/oeubVW9LooTaJT4mrZZExc7z15pszTPY5 tXog== MIME-Version: 1.0 Received: by 10.182.2.233 with SMTP id 9mr20417371obx.11.1344276891082; Mon, 06 Aug 2012 11:14:51 -0700 (PDT) Received: by 10.76.102.111 with HTTP; Mon, 6 Aug 2012 11:14:51 -0700 (PDT) Date: Mon, 6 Aug 2012 11:14:51 -0700 Message-ID: Subject: [PATCH 1/3] Replace i2f() in r600_blit.c with an optimized version. From: Steven Fuerst To: Alex Deucher X-Mailman-Approved-At: Mon, 06 Aug 2012 11:18:21 -0700 Cc: dri-devel@lists.freedesktop.org X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+patchwork-dri-devel=patchwork.kernel.org@lists.freedesktop.org Errors-To: dri-devel-bounces+patchwork-dri-devel=patchwork.kernel.org@lists.freedesktop.org Replace i2f() in r600_blit.c with an optimized version. We use __fls() to find the most significant bit. Using that, the loop can be avoided. A second trick is to use the mod(32) behaviour of the rotate instructions on x86 to expand the range of the unsigned int to float conversion to the full 32 bits. The routine is now exact up to 2^24. Above that, we truncate which is equivalent to rounding towards zero. Signed-off-by: Steven Fuerst --- drivers/gpu/drm/radeon/r600_blit.c | 52 +++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 22 deletions(-) diff --git a/drivers/gpu/drm/radeon/r600_blit.c b/drivers/gpu/drm/radeon/r600_blit.c index 3c031a4..f0ce441 100644 --- a/drivers/gpu/drm/radeon/r600_blit.c +++ b/drivers/gpu/drm/radeon/r600_blit.c @@ -489,29 +489,37 @@ set_default_state(drm_radeon_private_t *dev_priv) ADVANCE_RING(); } -static uint32_t i2f(uint32_t input) +/* 23 bits of float fractional data */ +#define I2F_FRAC_BITS 23 +#define I2F_MASK ((1 << I2F_FRAC_BITS) - 1) + +/* + * Converts unsigned integer into 32-bit IEEE floating point representation. + * Will be exact from 0 to 2^24. Above that, we round towards zero + * as the fractional bits will not fit in a float. (It would be better to + * round towards even as the fpu does, but that is slower.) + * This routine depends on the mod(32) behaviour of the rotate instructions + * on x86. + */ +static uint32_t i2f(uint32_t x) { - u32 result, i, exponent, fraction; - - if ((input & 0x3fff) == 0) - result = 0; /* 0 is a special case */ - else { - exponent = 140; /* exponent biased by 127; */ - fraction = (input & 0x3fff) << 10; /* cheat and only - handle numbers below 2^^15 */ - for (i = 0; i < 14; i++) { - if (fraction & 0x800000) - break; - else { - fraction = fraction << 1; /* keep - shifting left until top bit = 1 */ - exponent = exponent - 1; - } - } - result = exponent << 23 | (fraction & 0x7fffff); /* mask - off top bit; assumed 1 */ - } - return result; + uint32_t msb, exponent, fraction; + + /* Zero is special */ + if (!x) return 0; + + /* Get location of the most significant bit */ + msb = __fls(x); + + /* + * Use a rotate instead of a shift because that works both leftwards + * and rightwards due to the mod(32) beahviour. This means we don't + * need to check to see if we are above 2^24 or not. + */ + fraction = ror32(x, msb - I2F_FRAC_BITS) & I2F_MASK; + exponent = (127 + msb) << I2F_FRAC_BITS; + + return fraction + exponent; }