io/nge/nge_atomic.c

	nge_atomic.c revision 6f3e57ac9d0b054c3169579f3422080b8ba10105
/*
 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * This file may contain confidential information of Nvidia
 * and should not be distributed in source form without approval
 * from Sun Legal.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include "nge.h"

/*
 * Atomically decrement a counter, but only if it will remain
 * positive (>=0) afterwards.
 */
boolean_t
nge_atomic_decrease(uint64_t *count_p, uint64_t n)
{
    uint64_t oldval;
    uint64_t newval;

    /* ATOMICALLY */
    do {
        oldval = *count_p;
        newval = oldval - n;
        if (oldval < n)
            return (B_FALSE);
    } while (cas64(count_p, oldval, newval) != oldval);

    return (B_TRUE);
}

/*
 * Atomically increment a counter
 */
void
nge_atomic_increase(uint64_t *count_p, uint64_t n)
{
    uint64_t oldval;
    uint64_t newval;

    /* ATOMICALLY */
    do {
        oldval = *count_p;
        newval = oldval + n;
    } while (cas64(count_p, oldval, newval) != oldval);
}


/*
 * Atomically shift a 32-bit word left, returning
 * the value it had *before* the shift was applied
 */
uint32_t
nge_atomic_shl32(uint32_t *sp, uint_t count)
{
    uint32_t oldval;
    uint32_t newval;

    /* ATOMICALLY */
    do {
        oldval = *sp;
        newval = oldval << count;
    } while (cas32(sp, oldval, newval) != oldval);

    return (oldval);
}