UefiCpuPkg/Library/BaseUefiCpuLib/X64/InitializeFpu.S

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   2 #*
   3 #*   Copyright 2009, Intel Corporation
   4 #*   All rights reserved. This program and the accompanying materials
   5 #*   are licensed and made available under the terms and conditions of the BSD License
   6 #*   which accompanies this distribution.  The full text of the license may be found at
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   9 #*   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 #*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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  13 #------------------------------------------------------------------------------
  14
  15
  16 #
  17 # Float control word initial value:
  18 # all exceptions masked, double-precision, round-to-nearest
  19 #
  20 ASM_PFX(mFpuControlWord): .word     0x027F
  21 #
  22 # Multimedia-extensions control word:
  23 # all exceptions masked, round-to-nearest, flush to zero for masked underflow
  24 #
  25 ASM_PFX(mMmxControlWord): .long     0x01F80
  26
  27 #
  28 # Initializes floating point units for requirement of UEFI specification.
  29 #
  30 # This function initializes floating-point control word to 0x027F (all exceptions
  31 # masked,double-precision, round-to-nearest) and multimedia-extensions control word
  32 # (if supported) to 0x1F80 (all exceptions masked, round-to-nearest, flush to zero
  33 # for masked underflow).
  34 #
  35 ASM_GLOBAL ASM_PFX(InitializeFloatingPointUnits)
  36 ASM_PFX(InitializeFloatingPointUnits):
  37
  38     #
  39     # Initialize floating point units
  40     #
  41     finit
  42     fldcw   ASM_PFX(mFpuControlWord)
  43
  44     #
  45     # Set OSFXSR bit 9 in CR4
  46     #
  47     movq    %cr4, %rax
  48     or      $200, %rax
  49     movq    %rax, %cr4
  50
  51     ldmxcsr ASM_PFX(mMmxControlWord)
  52
  53     ret
  54