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authorJoakim Tjernlund <joakim.tjernlund@transmode.se>2005-09-17 12:00:06 +0000
committerJoakim Tjernlund <joakim.tjernlund@transmode.se>2005-09-17 12:00:06 +0000
commit89856a5b7e6894c36df6601365d429975df0d18a (patch)
treee7abf73fde83b13cdf6b1bb664230b61c6baa55c /libc
parent693835153538708184290e6e3950efd726bf2baf (diff)
Add atomic support for PPC.
Merge glibc bits/atomic.h powerpc32/bits/atomic.h powerpc64/bits/atomic.h into one file
Diffstat (limited to 'libc')
-rw-r--r--libc/sysdeps/linux/powerpc/bits/atomic.h607
1 files changed, 607 insertions, 0 deletions
diff --git a/libc/sysdeps/linux/powerpc/bits/atomic.h b/libc/sysdeps/linux/powerpc/bits/atomic.h
new file mode 100644
index 000000000..447195538
--- /dev/null
+++ b/libc/sysdeps/linux/powerpc/bits/atomic.h
@@ -0,0 +1,607 @@
+/* Atomic operations. PowerPC Common version.
+ Copyright (C) 2003, 2004 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include <bits/wordsize.h>
+
+#if __WORDSIZE == 64
+/* Atomic operations. PowerPC64 version.
+ Copyright (C) 2003, 2004 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+/* The 32-bit exchange_bool is different on powerpc64 because the subf
+ does signed 64-bit arthmatic while the lwarx is 32-bit unsigned
+ (a load word and zero (high 32) form) load.
+ In powerpc64 register values are 64-bit by default, including oldval.
+ The value in old val unknown sign extension, lwarx loads the 32-bit
+ value as unsigned. So we explicitly clear the high 32 bits in oldval. */
+# define __arch_compare_and_exchange_bool_32_acq(mem, newval, oldval) \
+({ \
+ unsigned int __tmp, __tmp2; \
+ __asm __volatile (" clrldi %1,%1,32\n" \
+ "1: lwarx %0,0,%2\n" \
+ " subf. %0,%1,%0\n" \
+ " bne 2f\n" \
+ " stwcx. %4,0,%2\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&r" (__tmp), "=r" (__tmp2) \
+ : "b" (mem), "1" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+# define __arch_compare_and_exchange_bool_32_rel(mem, newval, oldval) \
+({ \
+ unsigned int __tmp, __tmp2; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ " clrldi %1,%1,32\n" \
+ "1: lwarx %0,0,%2\n" \
+ " subf. %0,%1,%0\n" \
+ " bne 2f\n" \
+ " stwcx. %4,0,%2\n" \
+ " bne- 1b\n" \
+ "2: " \
+ : "=&r" (__tmp), "=r" (__tmp2) \
+ : "b" (mem), "1" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+/*
+ * Only powerpc64 processors support Load doubleword and reserve index (ldarx)
+ * and Store doubleword conditional indexed (stdcx) instructions. So here
+ * we define the 64-bit forms.
+ */
+# define __arch_compare_and_exchange_bool_64_acq(mem, newval, oldval) \
+({ \
+ unsigned long __tmp; \
+ __asm __volatile ( \
+ "1: ldarx %0,0,%1\n" \
+ " subf. %0,%2,%0\n" \
+ " bne 2f\n" \
+ " stdcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&r" (__tmp) \
+ : "b" (mem), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+# define __arch_compare_and_exchange_bool_64_rel(mem, newval, oldval) \
+({ \
+ unsigned long __tmp; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: ldarx %0,0,%1\n" \
+ " subf. %0,%2,%0\n" \
+ " bne 2f\n" \
+ " stdcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " \
+ : "=&r" (__tmp) \
+ : "b" (mem), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+#define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __tmp; \
+ __typeof (mem) __memp = (mem); \
+ __asm __volatile ( \
+ "1: ldarx %0,0,%1\n" \
+ " cmpd %0,%2\n" \
+ " bne 2f\n" \
+ " stdcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&r" (__tmp) \
+ : "b" (__memp), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp; \
+ })
+
+#define __arch_compare_and_exchange_val_64_rel(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __tmp; \
+ __typeof (mem) __memp = (mem); \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: ldarx %0,0,%1\n" \
+ " cmpd %0,%2\n" \
+ " bne 2f\n" \
+ " stdcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " \
+ : "=&r" (__tmp) \
+ : "b" (__memp), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp; \
+ })
+
+# define __arch_atomic_exchange_64_acq(mem, value) \
+ ({ \
+ __typeof (*mem) __val; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: ldarx %0,0,%2\n" \
+ " stdcx. %3,0,%2\n" \
+ " bne- 1b\n" \
+ " " __ARCH_ACQ_INSTR \
+ : "=&r" (__val), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+# define __arch_atomic_exchange_64_rel(mem, value) \
+ ({ \
+ __typeof (*mem) __val; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: ldarx %0,0,%2\n" \
+ " stdcx. %3,0,%2\n" \
+ " bne- 1b" \
+ : "=&r" (__val), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+# define __arch_atomic_exchange_and_add_64(mem, value) \
+ ({ \
+ __typeof (*mem) __val, __tmp; \
+ __asm __volatile ("1: ldarx %0,0,%3\n" \
+ " add %1,%0,%4\n" \
+ " stdcx. %1,0,%3\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=&r" (__tmp), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+# define __arch_atomic_increment_val_64(mem) \
+ ({ \
+ __typeof (*(mem)) __val; \
+ __asm __volatile ("1: ldarx %0,0,%2\n" \
+ " addi %0,%0,1\n" \
+ " stdcx. %0,0,%2\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+# define __arch_atomic_decrement_val_64(mem) \
+ ({ \
+ __typeof (*(mem)) __val; \
+ __asm __volatile ("1: ldarx %0,0,%2\n" \
+ " subi %0,%0,1\n" \
+ " stdcx. %0,0,%2\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+# define __arch_atomic_decrement_if_positive_64(mem) \
+ ({ int __val, __tmp; \
+ __asm __volatile ("1: ldarx %0,0,%3\n" \
+ " cmpdi 0,%0,0\n" \
+ " addi %1,%0,-1\n" \
+ " ble 2f\n" \
+ " stdcx. %1,0,%3\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&b" (__val), "=&r" (__tmp), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+/*
+ * All powerpc64 processors support the new "light weight" sync (lwsync).
+ */
+# define atomic_read_barrier() __asm ("lwsync" ::: "memory")
+/*
+ * "light weight" sync can also be used for the release barrier.
+ */
+# ifndef UP
+# define __ARCH_REL_INSTR "lwsync"
+# endif
+
+#else
+/* Atomic operations. PowerPC32 version.
+ Copyright (C) 2003, 2004 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+/*
+ * The 32-bit exchange_bool is different on powerpc64 because the subf
+ * does signed 64-bit arthmatic while the lwarx is 32-bit unsigned
+ * (a load word and zero (high 32) form). So powerpc64 has a slightly
+ * different version in sysdeps/powerpc/powerpc64/bits/atomic.h.
+ */
+# define __arch_compare_and_exchange_bool_32_acq(mem, newval, oldval) \
+({ \
+ unsigned int __tmp; \
+ __asm __volatile ( \
+ "1: lwarx %0,0,%1\n" \
+ " subf. %0,%2,%0\n" \
+ " bne 2f\n" \
+ " stwcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&r" (__tmp) \
+ : "b" (mem), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+# define __arch_compare_and_exchange_bool_32_rel(mem, newval, oldval) \
+({ \
+ unsigned int __tmp; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: lwarx %0,0,%1\n" \
+ " subf. %0,%2,%0\n" \
+ " bne 2f\n" \
+ " stwcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " \
+ : "=&r" (__tmp) \
+ : "b" (mem), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp != 0; \
+})
+
+/* Powerpc32 processors don't implement the 64-bit (doubleword) forms of
+ load and reserve (ldarx) and store conditional (stdcx.) instructions.
+ So for powerpc32 we stub out the 64-bit forms. */
+# define __arch_compare_and_exchange_bool_64_acq(mem, newval, oldval) \
+ (abort (), 0)
+
+# define __arch_compare_and_exchange_val_64_acq(mem, newval, oldval) \
+ (abort (), (__typeof (*mem)) 0)
+
+# define __arch_compare_and_exchange_bool_64_rel(mem, newval, oldval) \
+ (abort (), 0)
+
+# define __arch_compare_and_exchange_val_64_rel(mem, newval, oldval) \
+ (abort (), (__typeof (*mem)) 0)
+
+# define __arch_atomic_exchange_64_acq(mem, value) \
+ ({ abort (); (*mem) = (value); })
+
+# define __arch_atomic_exchange_64_rel(mem, value) \
+ ({ abort (); (*mem) = (value); })
+
+# define __arch_atomic_exchange_and_add_64(mem, value) \
+ ({ abort (); (*mem) = (value); })
+
+# define __arch_atomic_increment_val_64(mem) \
+ ({ abort (); (*mem)++; })
+
+# define __arch_atomic_decrement_val_64(mem) \
+ ({ abort (); (*mem)--; })
+
+# define __arch_atomic_decrement_if_positive_64(mem) \
+ ({ abort (); (*mem)--; })
+
+/*
+ * Older powerpc32 processors don't support the new "light weight"
+ * sync (lwsync). So the only safe option is to use normal sync
+ * for all powerpc32 applications.
+ */
+# define atomic_read_barrier() __asm ("sync" ::: "memory")
+
+#endif
+
+#include <stdint.h>
+
+typedef int32_t atomic32_t;
+typedef uint32_t uatomic32_t;
+typedef int_fast32_t atomic_fast32_t;
+typedef uint_fast32_t uatomic_fast32_t;
+
+typedef int64_t atomic64_t;
+typedef uint64_t uatomic64_t;
+typedef int_fast64_t atomic_fast64_t;
+typedef uint_fast64_t uatomic_fast64_t;
+
+typedef intptr_t atomicptr_t;
+typedef uintptr_t uatomicptr_t;
+typedef intmax_t atomic_max_t;
+typedef uintmax_t uatomic_max_t;
+
+/*
+ * Powerpc does not have byte and halfword forms of load and reserve and
+ * store conditional. So for powerpc we stub out the 8- and 16-bit forms.
+ */
+#define __arch_compare_and_exchange_bool_8_acq(mem, newval, oldval) \
+ (abort (), 0)
+
+#define __arch_compare_and_exchange_bool_16_acq(mem, newval, oldval) \
+ (abort (), 0)
+
+#define __arch_compare_and_exchange_bool_8_rel(mem, newval, oldval) \
+ (abort (), 0)
+
+#define __arch_compare_and_exchange_bool_16_rel(mem, newval, oldval) \
+ (abort (), 0)
+
+#ifdef UP
+# define __ARCH_ACQ_INSTR ""
+# define __ARCH_REL_INSTR ""
+#else
+# define __ARCH_ACQ_INSTR "isync"
+# ifndef __ARCH_REL_INSTR
+# define __ARCH_REL_INSTR "sync"
+# endif
+#endif
+
+#define atomic_full_barrier() __asm ("sync" ::: "memory")
+#define atomic_write_barrier() __asm ("eieio" ::: "memory")
+
+#define __arch_compare_and_exchange_val_32_acq(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __tmp; \
+ __typeof (mem) __memp = (mem); \
+ __asm __volatile ( \
+ "1: lwarx %0,0,%1\n" \
+ " cmpw %0,%2\n" \
+ " bne 2f\n" \
+ " stwcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&r" (__tmp) \
+ : "b" (__memp), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp; \
+ })
+
+#define __arch_compare_and_exchange_val_32_rel(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __tmp; \
+ __typeof (mem) __memp = (mem); \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: lwarx %0,0,%1\n" \
+ " cmpw %0,%2\n" \
+ " bne 2f\n" \
+ " stwcx. %3,0,%1\n" \
+ " bne- 1b\n" \
+ "2: " \
+ : "=&r" (__tmp) \
+ : "b" (__memp), "r" (oldval), "r" (newval) \
+ : "cr0", "memory"); \
+ __tmp; \
+ })
+
+#define __arch_atomic_exchange_32_acq(mem, value) \
+ ({ \
+ __typeof (*mem) __val; \
+ __asm __volatile ( \
+ "1: lwarx %0,0,%2\n" \
+ " stwcx. %3,0,%2\n" \
+ " bne- 1b\n" \
+ " " __ARCH_ACQ_INSTR \
+ : "=&r" (__val), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define __arch_atomic_exchange_32_rel(mem, value) \
+ ({ \
+ __typeof (*mem) __val; \
+ __asm __volatile (__ARCH_REL_INSTR "\n" \
+ "1: lwarx %0,0,%2\n" \
+ " stwcx. %3,0,%2\n" \
+ " bne- 1b" \
+ : "=&r" (__val), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define __arch_atomic_exchange_and_add_32(mem, value) \
+ ({ \
+ __typeof (*mem) __val, __tmp; \
+ __asm __volatile ("1: lwarx %0,0,%3\n" \
+ " add %1,%0,%4\n" \
+ " stwcx. %1,0,%3\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=&r" (__tmp), "=m" (*mem) \
+ : "b" (mem), "r" (value), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define __arch_atomic_increment_val_32(mem) \
+ ({ \
+ __typeof (*(mem)) __val; \
+ __asm __volatile ("1: lwarx %0,0,%2\n" \
+ " addi %0,%0,1\n" \
+ " stwcx. %0,0,%2\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define __arch_atomic_decrement_val_32(mem) \
+ ({ \
+ __typeof (*(mem)) __val; \
+ __asm __volatile ("1: lwarx %0,0,%2\n" \
+ " subi %0,%0,1\n" \
+ " stwcx. %0,0,%2\n" \
+ " bne- 1b" \
+ : "=&b" (__val), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define __arch_atomic_decrement_if_positive_32(mem) \
+ ({ int __val, __tmp; \
+ __asm __volatile ("1: lwarx %0,0,%3\n" \
+ " cmpwi 0,%0,0\n" \
+ " addi %1,%0,-1\n" \
+ " ble 2f\n" \
+ " stwcx. %1,0,%3\n" \
+ " bne- 1b\n" \
+ "2: " __ARCH_ACQ_INSTR \
+ : "=&b" (__val), "=&r" (__tmp), "=m" (*mem) \
+ : "b" (mem), "m" (*mem) \
+ : "cr0", "memory"); \
+ __val; \
+ })
+
+#define atomic_compare_and_exchange_val_acq(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_compare_and_exchange_val_32_acq(mem, newval, oldval); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_compare_and_exchange_val_64_acq(mem, newval, oldval); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_compare_and_exchange_val_rel(mem, newval, oldval) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_compare_and_exchange_val_32_rel(mem, newval, oldval); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_compare_and_exchange_val_64_rel(mem, newval, oldval); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_exchange_acq(mem, value) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_atomic_exchange_32_acq (mem, value); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_atomic_exchange_64_acq (mem, value); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_exchange_rel(mem, value) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_atomic_exchange_32_rel (mem, value); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_atomic_exchange_64_rel (mem, value); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_exchange_and_add(mem, value) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_atomic_exchange_and_add_32 (mem, value); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_atomic_exchange_and_add_64 (mem, value); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_increment_val(mem) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*(mem)) == 4) \
+ __result = __arch_atomic_increment_val_32 (mem); \
+ else if (sizeof (*(mem)) == 8) \
+ __result = __arch_atomic_increment_val_64 (mem); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_increment(mem) ({ atomic_increment_val (mem); (void) 0; })
+
+#define atomic_decrement_val(mem) \
+ ({ \
+ __typeof (*(mem)) __result; \
+ if (sizeof (*(mem)) == 4) \
+ __result = __arch_atomic_decrement_val_32 (mem); \
+ else if (sizeof (*(mem)) == 8) \
+ __result = __arch_atomic_decrement_val_64 (mem); \
+ else \
+ abort (); \
+ __result; \
+ })
+
+#define atomic_decrement(mem) ({ atomic_decrement_val (mem); (void) 0; })
+
+
+/* Decrement *MEM if it is > 0, and return the old value. */
+#define atomic_decrement_if_positive(mem) \
+ ({ __typeof (*(mem)) __result; \
+ if (sizeof (*mem) == 4) \
+ __result = __arch_atomic_decrement_if_positive_32 (mem); \
+ else if (sizeof (*mem) == 8) \
+ __result = __arch_atomic_decrement_if_positive_64 (mem); \
+ else \
+ abort (); \
+ __result; \
+ })