usr/src/lib/libc/amd64/fp/fpstart.c

   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 (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 /*
  28  *      Copyright (c) 1990, 1991 UNIX System Laboratories, Inc.
  29  *      Copyright (c) 1988 AT&T
  30  *        All Rights Reserved
  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 "lint.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 int     __flt_rounds;           /* ANSI rounding mode */
  52
  53 void
  54 __fpstart()
  55 {
  56         int _fp_hw;             /* default: bss: 0 == no hardware */
  57
  58         /*
  59          * query OS for HW status and ensure the x87 and (optional)
  60          * SSE control words are (will be) set correctly.
  61          * This "cannot fail".
  62          */
  63         (void) sysi86(SI86FPSTART,
  64             &_fp_hw, FPU_CW_INIT, SSE_MXCSR_INIT);
  65
  66         /*
  67          * At this point the x87 fp environment that has been (or more
  68          * hopefully, will be) established by the kernel is:
  69          *
  70          * affine infinity      0x1000
  71          * round to nearest     0x0000
  72          * 64-bit doubles       0x0300
  73          * precision, underflow, overflow, zero-divide, denorm, invalid masked
  74          *                      0x003f
  75          *
  76          * which conforms to the 4th edition i386 ABI definition.
  77          *
  78          * Additionally, if we have SSE hardware, we've also masked all
  79          * the same traps, and have round to nearest.
  80          */
  81
  82         __flt_rounds = 1;       /* ANSI way of saying round-to-nearest */
  83 }