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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License (the "License").
      6  * You may not use this file except in compliance with the License.
      7  *
      8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      9  * or http://www.opensolaris.org/os/licensing.
     10  * See the License for the specific language governing permissions
     11  * and limitations under the License.
     12  *
     13  * When distributing Covered Code, include this CDDL HEADER in each
     14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     15  * If applicable, add the following below this CDDL HEADER, with the
     16  * fields enclosed by brackets "[]" replaced with your own identifying
     17  * information: Portions Copyright [yyyy] [name of copyright owner]
     18  *
     19  * CDDL HEADER END
     20  */
     21 
     22 /*
     23  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
     24  * Use is subject to license terms.
     25  */
     26 
     27 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     28 
     29 #include "nge.h"
     30 
     31 /*
     32  * Atomically decrement a counter, but only if it will remain
     33  * positive (>=0) afterwards.
     34  */
     35 boolean_t
     36 nge_atomic_decrease(uint64_t *count_p, uint64_t n)
     37 {
     38 	uint64_t oldval;
     39 	uint64_t newval;
     40 
     41 	/* ATOMICALLY */
     42 	do {
     43 		oldval = *count_p;
     44 		newval = oldval - n;
     45 		if (oldval < n)
     46 			return (B_FALSE);
     47 	} while (cas64(count_p, oldval, newval) != oldval);
     48 
     49 	return (B_TRUE);
     50 }
     51 
     52 /*
     53  * Atomically increment a counter
     54  */
     55 void
     56 nge_atomic_increase(uint64_t *count_p, uint64_t n)
     57 {
     58 	uint64_t oldval;
     59 	uint64_t newval;
     60 
     61 	/* ATOMICALLY */
     62 	do {
     63 		oldval = *count_p;
     64 		newval = oldval + n;
     65 	} while (cas64(count_p, oldval, newval) != oldval);
     66 }
     67 
     68 
     69 /*
     70  * Atomically shift a 32-bit word left, returning
     71  * the value it had *before* the shift was applied
     72  */
     73 uint32_t
     74 nge_atomic_shl32(uint32_t *sp, uint_t count)
     75 {
     76 	uint32_t oldval;
     77 	uint32_t newval;
     78 
     79 	/* ATOMICALLY */
     80 	do {
     81 		oldval = *sp;
     82 		newval = oldval << count;
     83 	} while (cas32(sp, oldval, newval) != oldval);
     84 
     85 	return (oldval);
     86 }
     87