libatomic/config/arm/exch_n.c

   1 /* Copyright (C) 2012-2013 Free Software Foundation, Inc.
   2    Contributed by Richard Henderson <rth@redhat.com>.
   3
   4    This file is part of the GNU Atomic Library (libatomic).
   5
   6    Libatomic is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
  12    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  13    FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  14    more details.
  15
  16    Under Section 7 of GPL version 3, you are granted additional
  17    permissions described in the GCC Runtime Library Exception, version
  18    3.1, as published by the Free Software Foundation.
  19
  20    You should have received a copy of the GNU General Public License and
  21    a copy of the GCC Runtime Library Exception along with this program;
  22    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23    <http://www.gnu.org/licenses/>.  */
  24
  25 #include <libatomic_i.h>
  26 #include <arm-config.h>
  27
  28
  29 /* When using STREX to implement sub-word exchange, we can do much better
  30    than the compiler by using the APSR.GE and APSR.C flags.  */
  31
  32 #if !DONE && HAVE_STREX && !HAVE_STREXBH && N == 2
  33 UTYPE
  34 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  35 {
  36   UWORD t1, t2;
  37   UTYPE oldval;
  38
  39   __atomic_thread_fence (__ATOMIC_SEQ_CST);
  40
  41   /* In the N=2 case, there are only two cases for MPTR: mptr % 4 == {0,2}.
  42      Rather than computing a variable shift for this, we can store the one
  43      bit of misalignment in the carry flag, and use conditional constant
  44      shifts instead.  This saves a register.  */
  45 #ifdef __ARMEB__
  46 # define HI     "cc"                            /* iff value is in high half */
  47 # define LO     "cs"                            /* iff value is in low half */
  48 #else
  49 # define HI     "cs"
  50 # define LO     "cc"
  51 #endif
  52
  53   asm volatile (
  54                 "lsrs   %[t2],%[ptr],#2\n"      /* carry = mptr & 2 */
  55         "       bic     %[ptr],%[ptr],#3\n"     /* align mptr */
  56         "       itt     "HI"\n"
  57         "       lsl"HI" %[t1],%[t1],#16\n"      /* shift mask into place */
  58         "       lsl"HI" %[new],%[new],#16\n"    /* shift newval into place */
  59         "       uadd16  %[t1],%[t1],%[t1]\n"    /* copy mask into APSR.GE */
  60         "0:     ldrex   %[t2],[%[ptr]]\n"
  61         "       ite     "LO"\n"
  62         "       uxth"LO" %[old],%[t2]\n"        /* return old value */
  63         "       uxth"HI" %[old],%[t2], ror #16\n"
  64         "       sel     %[t1],%[new],%[t2]\n"   /* merge newval */
  65         "       strex   %[t2],%[t1],[%[ptr]]\n"
  66         "       tst     %[t2],%[t2]\n"          /* dont clobber carry */
  67         "       bne     0b"
  68         : [old] "=&r"(oldval), [t1] "=&r"(t1), [t2] "=&r"(t2),
  69           [ptr] "+r"(mptr), [new] "+r"(newval)
  70         : "1"(0xffff)
  71         : "memory");
  72
  73   __atomic_thread_fence (__ATOMIC_SEQ_CST);
  74
  75   return oldval;
  76 }
  77
  78 #define DONE 1
  79 #endif /* !HAVE_STREXBH && N == 2 */
  80
  81
  82 #if !DONE && HAVE_STREX && !HAVE_STREXBH && N == 1
  83 UTYPE
  84 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  85 {
  86   UWORD *wptr, woldval, wnewval, shift, mask, t1, t2;
  87
  88   __atomic_thread_fence (__ATOMIC_SEQ_CST);
  89
  90   wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  91   shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ INVERT_MASK_1;
  92   mask = MASK_1 << shift;
  93   wnewval = newval << shift;
  94
  95   asm volatile (
  96                 "uadd8  %[t1],%[t1],%[t1]\n"    /* move mask to APSR.GE */
  97         "0:     ldrex   %[old],[%[wptr]]\n"
  98         "       sel     %[t1],%[new],%[old]\n"  /* merge newval */
  99         "       strex   %[t2],%[t1],[%[wptr]]\n"
 100         "       cmp     %[t2],#0\n"
 101         "       bne     0b"
 102         : [old] "=&r"(woldval), [t1] "=&r"(t1), [t2] "=&r"(t2)
 103         : [new] "r"(wnewval), [wptr] "r"(wptr), "1"(mask)
 104         : "memory");
 105
 106   __atomic_thread_fence (__ATOMIC_SEQ_CST);
 107
 108   return woldval >> shift;
 109 }
 110
 111 #define DONE 1
 112 #endif /* !HAVE_STREXBH && N == 1 */
 113
 114 #include "../../exch_n.c"