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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 17 Jun 2017 11:25:31 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r320051 - head/sys/i386/isa
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Author: kib
Date: Sat Jun 17 11:25:31 2017
New Revision: 320051
URL: https://svnweb.freebsd.org/changeset/base/320051

Log:
  Correct translations between abridged and full x87 tags.
  
  Reported and tested by:	karnajit wangkhem <karnajitw@gmail.com>
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/i386/isa/npx.c

Modified: head/sys/i386/isa/npx.c
==============================================================================
--- head/sys/i386/isa/npx.c	Sat Jun 17 07:36:46 2017	(r320050)
+++ head/sys/i386/isa/npx.c	Sat Jun 17 11:25:31 2017	(r320051)
@@ -1108,7 +1108,7 @@ npx_fill_fpregs_xmm1(struct savexmm *sv_xmm, struct sa
 		sv_87->sv_ac[i] = sv_xmm->sv_fp[i].fp_acc;
 		if ((penv_xmm->en_tw & (1 << i)) != 0)
 			/* zero and special are set as valid */
-			penv_87->en_tw &= ~(3 << i);
+			penv_87->en_tw &= ~(3 << i * 2);
 	}
 }
 
@@ -1139,11 +1139,16 @@ npx_set_fpregs_xmm(struct save87 *sv_87, struct savexm
 	penv_xmm->en_foo = penv_87->en_foo;
 	penv_xmm->en_fos = penv_87->en_fos;
 
-	/* FPU registers and tags */
+	/*
+	 * FPU registers and tags.
+	 * Abridged  /  Full translation (values in binary), see FXSAVE spec.
+	 * 0		11
+	 * 1		00, 01, 10
+	 */
 	penv_xmm->en_tw = 0;
 	for (i = 0; i < 8; ++i) {
 		sv_xmm->sv_fp[i].fp_acc = sv_87->sv_ac[i];
-		if ((penv_87->en_tw && (3 << i)) != (3 << i))
+		if ((penv_87->en_tw & (3 << i * 2)) != (3 << i * 2))
 		    penv_xmm->en_tw |= 1 << i;
 	}
 }