1  /* Set FP exception mask and rounding mode.
       2     Copyright (C) 1996-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library.  If not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <fpu_control.h>
      20  #include <fenv_libc.h>
      21  
      22  
      23  #define convert_bit(M, F, T)		\
      24      ((T) < (F)				\
      25       ? ((M) / ((F) / (T))) & (T)	\
      26       : ((M) & (F)) * ((T) / (F)))
      27  
      28  
      29  void
      30  __setfpucw (fpu_control_t fpu_control)
      31  {
      32    unsigned long fpcr, swcr, fc = (int)fpu_control;
      33  
      34    /* ??? If this was a real external interface we'd want to read the current
      35       exception state with __ieee_get_fp_control.  But this is an internal
      36       function only called at process startup, so there's no point in trying
      37       to preserve exceptions that cannot have been raised yet.  Indeed, this
      38       entire function is likely to be one big nop unless the user overrides
      39       the default __fpu_control variable.  */
      40  
      41    /* Convert the rounding mode from fpu_control.h format.  */
      42    const unsigned long conv_rnd
      43      = (  (FE_TOWARDZERO << (_FPU_RC_ZERO >> 8))
      44         | (FE_DOWNWARD << (_FPU_RC_DOWN >> 8))
      45         | (FE_TONEAREST << (_FPU_RC_NEAREST >> 8))
      46         | (FE_UPWARD << (_FPU_RC_UP >> 8)));
      47  
      48    fpcr = ((conv_rnd >> ((fc >> 8) & 3)) & 3) << FPCR_ROUND_SHIFT;
      49  
      50    /* Convert the exception mask from fpu_control.h format.  */
      51    swcr  = convert_bit (~fc, _FPU_MASK_IM, FE_INVALID >> SWCR_ENABLE_SHIFT);
      52    swcr |= convert_bit (~fc, _FPU_MASK_DM, FE_UNDERFLOW >> SWCR_ENABLE_SHIFT);
      53    swcr |= convert_bit (~fc, _FPU_MASK_ZM, FE_DIVBYZERO >> SWCR_ENABLE_SHIFT);
      54    swcr |= convert_bit (~fc, _FPU_MASK_OM, FE_OVERFLOW >> SWCR_ENABLE_SHIFT);
      55    swcr |= convert_bit (~fc, _FPU_MASK_PM, FE_INEXACT >> SWCR_ENABLE_SHIFT);
      56  
      57    /* Install everything.  */
      58    __fpu_control = fc;
      59    asm volatile ("mt_fpcr %0" : : "f"(fpcr));
      60    __ieee_set_fp_control(swcr);
      61  }