xref: /titanic_51/usr/src/lib/libc/amd64/fp/fpstart.c (revision 9512fe850e98fdd448c638ca63fdd92a8a510255)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License, Version 1.0 only
6  * (the "License").  You may not use this file except in compliance
7  * with the License.
8  *
9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
10  * or http://www.opensolaris.org/os/licensing.
11  * See the License for the specific language governing permissions
12  * and limitations under the License.
13  *
14  * When distributing Covered Code, include this CDDL HEADER in each
15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
16  * If applicable, add the following below this CDDL HEADER, with the
17  * fields enclosed by brackets "[]" replaced with your own identifying
18  * information: Portions Copyright [yyyy] [name of copyright owner]
19  *
20  * CDDL HEADER END
21  */
22 /*
23  *	Copyright (c) 1990, 1991 UNIX System Laboratories, Inc.
24  *	Copyright (c) 1988 AT&T
25  *	  All Rights Reserved
26  */
27 
28 /*
29  * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
30  * Use is subject to license terms.
31  */
32 
33 #pragma ident	"%Z%%M%	%I%	%E% SMI"
34 
35 /*
36  * Establish the default settings for the floating-point state for a C language
37  * program:
38  *	rounding mode		-- round to nearest default by OS,
39  *	exceptions enabled	-- all masked
40  *	sticky bits		-- all clear by default by OS.
41  *      precision control       -- double extended
42  */
43 
44 #pragma weak _fpstart = __fpstart
45 
46 #include "synonyms.h"
47 #include <sys/types.h>
48 #include <sys/sysi86.h>	/* for SI86FPHW/SI86FPSTART definitions */
49 #include <sys/fp.h>	/* for FPU_CW_INIT and SSE_MXCSR_INIT */
50 
51 extern int _private_sysi86();
52 
53 int	__flt_rounds;		/* ANSI rounding mode */
54 
55 void
56 __fpstart()
57 {
58 	int _fp_hw;		/* default: bss: 0 == no hardware */
59 
60 	/*
61 	 * query OS for HW status and ensure the x87 and (optional)
62 	 * SSE control words are (will be) set correctly.
63 	 * This "cannot fail".
64 	 */
65 	(void) _private_sysi86(SI86FPSTART,
66 	    &_fp_hw, FPU_CW_INIT, SSE_MXCSR_INIT);
67 
68 	/*
69 	 * At this point the x87 fp environment that has been (or more
70 	 * hopefully, will be) established by the kernel is:
71 	 *
72 	 * affine infinity	0x1000
73 	 * round to nearest	0x0000
74 	 * 64-bit doubles	0x0300
75 	 * precision, underflow, overflow, zero-divide, denorm, invalid masked
76 	 *			0x003f
77 	 *
78 	 * which conforms to the 4th edition i386 ABI definition.
79 	 *
80 	 * Additionally, if we have SSE hardware, we've also masked all
81 	 * the same traps, and have round to nearest.
82 	 */
83 
84 	__flt_rounds = 1;	/* ANSI way of saying round-to-nearest */
85 }
86