atomic.h

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/*
 * Copyright (C) 2005, 2007  Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

/* $Id: atomic.h,v 1.3 2007/06/19 23:47:18 tbox Exp $ */

#ifndef ISC_ATOMIC_H
#define ISC_ATOMIC_H 1

#include <isc/platform.h>
#include <isc/types.h>

#ifdef ISC_PLATFORM_USEGCCASM
/*
 * This routine atomically increments the value stored in 'p' by 'val', and
 * returns the previous value.
 */
static inline isc_int32_t
isc_atomic_xadd(isc_int32_t *p, int val) {
        isc_int32_t orig;

        /* add is a cheat, since MIPS has no mov instruction */
        __asm__ volatile (
            "1:"
            "ll $3, %1\n"
            "add %0, $0, $3\n"
            "add $3, $3, %2\n"
            "sc $3, %1\n"
            "beq $3, 0, 1b"
            : "=&r"(orig)
            : "m"(*p), "r"(val)
            : "memory", "$3"
                );

        return (orig);
}

/*
 * This routine atomically stores the value 'val' in 'p'.
 */
static inline void
isc_atomic_store(isc_int32_t *p, isc_int32_t val) {
        __asm__ volatile (
            "1:"
            "ll $3, %0\n"
            "add $3, $0, %1\n"
            "sc $3, %0\n"
            "beq $3, 0, 1b"
            :
            : "m"(*p), "r"(val)
            : "memory", "$3"
                );
}

/*
 * This routine atomically replaces the value in 'p' with 'val', if the
 * original value is equal to 'cmpval'.  The original value is returned in any
 * case.
 */
static inline isc_int32_t
isc_atomic_cmpxchg(isc_int32_t *p, int cmpval, int val) {
        isc_int32_t orig;

        __asm__ volatile(
            "1:"
            "ll $3, %1\n"
            "add %0, $0, $3\n"
            "bne $3, %2, 2f\n"
            "add $3, $0, %3\n"
            "sc $3, %1\n"
            "beq $3, 0, 1b\n"
            "2:"
            : "=&r"(orig)
            : "m"(*p), "r"(cmpval), "r"(val)
            : "memory", "$3"
                );

        return (orig);
}

#else /* !ISC_PLATFORM_USEGCCASM */

#error "unsupported compiler.  disable atomic ops by --disable-atomic"

#endif
#endif /* ISC_ATOMIC_H */

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