UefiCpuPkg/Library/BaseUefiCpuLib/X64/InitializeFpu.S

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   2 #*
   3 #*   Copyright 2009 - 2010, 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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  10 #*   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11 #*
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  13 #------------------------------------------------------------------------------
  14
  15 #
  16 # Initializes floating point units for requirement of UEFI specification.
  17 #
  18 # This function initializes floating-point control word to 0x027F (all exceptions
  19 # masked,double-precision, round-to-nearest) and multimedia-extensions control word
  20 # (if supported) to 0x1F80 (all exceptions masked, round-to-nearest, flush to zero
  21 # for masked underflow).
  22 #
  23 ASM_GLOBAL ASM_PFX(InitializeFloatingPointUnits)
  24 ASM_PFX(InitializeFloatingPointUnits):
  25
  26     #
  27     # Initialize floating point units
  28     #
  29     finit
  30
  31     #
  32     # Float control word initial value:
  33     # all exceptions masked, double-precision, round-to-nearest
  34     #
  35     pushq   $0x027F
  36     lea     (%rsp), %rax
  37     fldcw   (%rax)
  38     popq    %rax
  39
  40     #
  41     # Set OSFXSR bit 9 in CR4
  42     #
  43     movq    %cr4, %rax
  44     or      $0x200, %rax
  45     movq    %rax, %cr4
  46
  47     #
  48     # Multimedia-extensions control word:
  49     # all exceptions masked, round-to-nearest, flush to zero for masked underflow
  50     #
  51     pushq   $0x01F80
  52     lea     (%rsp), %rax
  53     ldmxcsr (%rax)
  54     popq    %rax
  55
  56     ret
  57