• Maciej W. Rozycki's avatar
    MIPS: math-emu: Add IEEE Std 754-2008 NaN encoding emulation · 90d53a91
    Maciej W. Rozycki authored
    Implement IEEE Std 754-2008 NaN encoding wired to the state of the
    FCSR.NAN2008 bit.  Make the interpretation of the quiet bit in NaN data
    as follows:
    
    * in the legacy mode originally defined by the MIPS architecture the
      value of 1 denotes an sNaN whereas the value of 0 denotes a qNaN,
    
    * in the 2008 mode introduced with revision 5 of the MIPS architecture
      the value of 0 denotes an sNaN whereas the value of 1 denotes a qNaN,
      following the definition of the preferred NaN encoding introduced with
      IEEE Std 754-2008.
    
    In the 2008 mode, following the requirement of the said standard, quiet
    an sNaN where needed by setting the quiet bit to 1 and leaving all the
    NaN payload bits unchanged.
    
    Update format conversion operations according to the rules set by IEEE
    Std 754-2008 and the MIPS architecture.  Specifically:
    
    * propagate NaN payload bits through conversions between floating-point
      formats such that as much information as possible is preserved and
      specifically a conversion from a narrower format to a wider format and
      then back to the original format does not change a qNaN payload in any
      way,
    
    * conversions from a floating-point to an integer format where the
      source is a NaN, infinity or a value that would convert to an integer
      outside the range of the result format produce, under the default
      exception handling, the respective values defined by the MIPS
      architecture.
    
    In full FPU emulation set the FIR.HAS2008 bit to 1, however do not make
    any further FCSR bits writable.
    Signed-off-by: default avatarMaciej W. Rozycki <macro@imgtec.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Matthew Fortune <Matthew.Fortune@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Cc: linux-kernel@vger.kernel.org
    Patchwork: https://patchwork.linux-mips.org/patch/11477/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    90d53a91