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      1 /*	$NetBSD: atomic_cas_by_cas32.c,v 1.4 2014/09/03 19:30:47 matt 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 #include "atomic_op_namespace.h"
     36 
     37 uint32_t _atomic_cas_32(volatile uint32_t *addr, uint32_t old, uint32_t new);
     38 uint16_t _atomic_cas_16(volatile uint16_t *addr, uint16_t old, uint16_t new);
     39 uint8_t _atomic_cas_8(volatile uint8_t *addr, uint8_t old, uint8_t new);
     40 
     41 /*
     42  * This file provides emulation of 8 bit and 16 bit CAS operations based on
     43  * 32 bit CAS.
     44  */
     45 uint16_t
     46 _atomic_cas_16(volatile uint16_t *addr, uint16_t old, uint16_t new)
     47 {
     48 	const uintptr_t base = (uintptr_t)addr & ~3;
     49 	const size_t off = (uintptr_t)addr - base;
     50 	volatile uint32_t * ptr = (volatile uint32_t *)base;
     51 	const size_t shift = off*8;
     52 	const uint32_t mask = 0x0ffff << shift;
     53 	const uint32_t old32_part = (uint32_t)old << shift;
     54 	const uint32_t new32_part = (uint32_t)new << shift;
     55 	uint32_t old32, new32;
     56 
     57 	do {
     58 		old32 = *ptr;
     59 		if ((old32 & mask) != old32_part)
     60 			return (uint16_t)((old32 & mask) >> shift);
     61 		new32 = (old32 & ~mask) | new32_part;
     62 	} while (_atomic_cas_32(ptr, old32, new32) != old32);
     63 
     64 	return old;
     65 }
     66 
     67 crt_alias(__sync_val_compare_and_swap_2,_atomic_cas_16)
     68 
     69 uint8_t
     70 _atomic_cas_8(volatile uint8_t *addr, uint8_t old, uint8_t new)
     71 {
     72 	const uintptr_t base = (uintptr_t)addr & ~3;
     73 	const size_t off = (uintptr_t)addr - base;
     74 	volatile uint32_t * ptr = (volatile uint32_t *)base;
     75 	const size_t shift = off*8;
     76 	const uint32_t mask = 0x0ff << shift;
     77 	const uint32_t old32_part = (uint32_t)old << shift;
     78 	const uint32_t new32_part = (uint32_t)new << shift;
     79 	uint32_t old32, new32;
     80 
     81 	do {
     82 		old32 = *ptr;
     83 		if ((old32 & mask) != old32_part)
     84 			return (uint8_t)((old32 & mask) >> shift);
     85 		new32 = (old32 & ~mask) | new32_part;
     86 	} while (_atomic_cas_32(ptr, old32, new32) != old32);
     87 
     88 	return old;
     89 }
     90 
     91 crt_alias(__sync_val_compare_and_swap_1,_atomic_cas_8)
     92