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 }