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atomic_cas_by_cas32.c revision 1.3.4.2 
      1 /*	$NetBSD: atomic_cas_by_cas32.c,v 1.3.4.2 2014/05/22 11:26:30 yamt Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2014 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Jason R. Thorpe.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/types.h>
     33 #include <sys/inttypes.h>
     34 
     35 uint32_t _atomic_cas_32(volatile uint32_t *addr, uint32_t old, uint32_t new);
     36 uint16_t _atomic_cas_16(volatile uint16_t *addr, uint16_t old, uint16_t new);
     37 uint8_t _atomic_cas_8(volatile uint8_t *addr, uint8_t old, uint8_t new);
     38 
     39 /*
     40  * This file provides emulation of 8 bit and 16 bit CAS operations based on
     41  * 32 bit CAS.
     42  */
     43 uint16_t
     44 _atomic_cas_16(volatile uint16_t *addr, uint16_t old, uint16_t new)
     45 {
     46 	const uintptr_t base = (uintptr_t)addr & ~3;
     47 	const size_t off = (uintptr_t)addr - base;
     48 	volatile uint32_t * ptr = (volatile uint32_t *)base;
     49 	const size_t shift = off*8;
     50 	const uint32_t mask = 0x0ffff << shift;
     51 	const uint32_t old32_part = (uint32_t)old << shift;
     52 	const uint32_t new32_part = (uint32_t)new << shift;
     53 	uint32_t old32, new32;
     54 
     55 	do {
     56 		old32 = *ptr;
     57 		if ((old32 & mask) != old32_part)
     58 			return (uint16_t)((old32 & mask) >> shift);
     59 		new32 = (old32 & ~mask) | new32_part;
     60 	} while (_atomic_cas_32(ptr, old32, new32) != old32);
     61 
     62 	return old;
     63 }
     64 
     65 uint8_t
     66 _atomic_cas_8(volatile uint8_t *addr, uint8_t old, uint8_t new)
     67 {
     68 	const uintptr_t base = (uintptr_t)addr & ~3;
     69 	const size_t off = (uintptr_t)addr - base;
     70 	volatile uint32_t * ptr = (volatile uint32_t *)base;
     71 	const size_t shift = off*8;
     72 	const uint32_t mask = 0x0ff << shift;
     73 	const uint32_t old32_part = (uint32_t)old << shift;
     74 	const uint32_t new32_part = (uint32_t)new << shift;
     75 	uint32_t old32, new32;
     76 
     77 	do {
     78 		old32 = *ptr;
     79 		if ((old32 & mask) != old32_part)
     80 			return (uint8_t)((old32 & mask) >> shift);
     81 		new32 = (old32 & ~mask) | new32_part;
     82 	} while (_atomic_cas_32(ptr, old32, new32) != old32);
     83 
     84 	return old;
     85 }
     86