1  /* NVPTX atomic operations
       2     Copyright (C) 2020-2023 Free Software Foundation, Inc.
       3     Contributed by Mentor Graphics.
       4  
       5     This file is free software; you can redistribute it and/or modify it
       6     under the terms of the GNU General Public License as published by the
       7     Free Software Foundation; either version 3, or (at your option) any
       8     later version.
       9  
      10     This file is distributed in the hope that it will be useful, but
      11     WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     General Public License for more details.
      14  
      15     Under Section 7 of GPL version 3, you are granted additional
      16     permissions described in the GCC Runtime Library Exception, version
      17     3.1, as published by the Free Software Foundation.
      18  
      19     You should have received a copy of the GNU General Public License and
      20     a copy of the GCC Runtime Library Exception along with this program;
      21     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      22     <http://www.gnu.org/licenses/>.  */
      23  
      24  #include <stdbool.h>
      25  
      26  /* Implement __sync_val_compare_and_swap and __sync_bool_compare_and_swap
      27     for 1 and 2-byte values (which are not natively supported) in terms of
      28     __sync_val_compare_and_swap for 4-byte values (which is supported).
      29     This assumes that the contents of the word surrounding the subword
      30     value that we are interested in are accessible as well (which should
      31     normally be the case).  Note that if the contents of the word surrounding
      32     the subword changes between the __sync_val_compare_and_swap_4 and the
      33     preceeding load of oldword, while the subword does not, the implementation
      34     loops, which may manifest worst-case as a hang.  */
      35  
      36  #define __SYNC_SUBWORD_COMPARE_AND_SWAP(TYPE, SIZE)			     \
      37  									     \
      38  TYPE									     \
      39  __sync_val_compare_and_swap_##SIZE (volatile void *vptr, TYPE oldval,	     \
      40  				    TYPE newval)			     \
      41  {									     \
      42    volatile TYPE *ptr = vptr;						     \
      43    volatile unsigned int *wordptr					     \
      44      = (volatile unsigned int *)((__UINTPTR_TYPE__) ptr & ~3UL);	     \
      45    int shift = ((__UINTPTR_TYPE__) ptr & 3UL) * 8;			     \
      46    unsigned int valmask = (1 << (SIZE * 8)) - 1;				     \
      47    unsigned int wordmask = ~(valmask << shift);				     \
      48    unsigned int oldword = *wordptr;					     \
      49    for (;;)								     \
      50      {									     \
      51        TYPE prevval = (oldword >> shift) & valmask;			     \
      52        /* Exit if the subword value previously read from memory is not */     \
      53        /* equal to the expected value OLDVAL.  */			     \
      54        if (__builtin_expect (prevval != oldval, 0))			     \
      55  	return prevval;							     \
      56        unsigned int newword = oldword & wordmask;			     \
      57        newword |= ((unsigned int) newval) << shift;			     \
      58        unsigned int prevword						     \
      59  	  = __sync_val_compare_and_swap_4 (wordptr, oldword, newword);	     \
      60        /* Exit only if the compare-and-swap succeeds on the whole word */     \
      61        /* (i.e. the contents of *WORDPTR have not changed since the last */   \
      62        /* memory read).  */						     \
      63        if (__builtin_expect (prevword == oldword, 1))			     \
      64  	return oldval;							     \
      65        oldword = prevword;						     \
      66      }									     \
      67  }									     \
      68  									     \
      69  bool									     \
      70  __sync_bool_compare_and_swap_##SIZE (volatile void *ptr, TYPE oldval,	     \
      71  				     TYPE newval)			     \
      72  {									     \
      73    return __sync_val_compare_and_swap_##SIZE (ptr, oldval, newval) == oldval; \
      74  }
      75  
      76  __SYNC_SUBWORD_COMPARE_AND_SWAP (unsigned char, 1)
      77  __SYNC_SUBWORD_COMPARE_AND_SWAP (unsigned short, 2)