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#include "u.h"
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#include "libc.h"
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/*
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 * first argument (l) is in r3 at entry.
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 * r3 contains return value upon return.
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 */
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int
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tas(long *x)
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{
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	int     v;
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	/*
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	 * this __asm__ works with gcc 2.95.2 (mac os x 10.1).
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	 * this assembly language destroys r0 (0), some other register (v),
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	 * r4 (x) and r5 (temp).
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	 */
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	__asm__("\n	sync\n"
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	"	li	r0,0\n"
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	"	mr	r4,%1		/* &l->val */\n"
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	"	lis	r5,0xdead	/* assemble constant 0xdeaddead */\n"
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	"	ori	r5,r5,0xdead	/* \" */\n"
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	"tas1:\n"
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	"	dcbf	r4,r0	/* cache flush; \"fix for 603x bug\" */\n"
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	"	lwarx	%0,r4,r0	/* v = l->val with reservation */\n"
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	"	cmp	cr0,0,%0,r0	/* v == 0 */\n"
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	"	bne	tas0\n"
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	"	stwcx.	r5,r4,r0   /* if (l->val same) l->val = 0xdeaddead */\n"
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	"	bne	tas1\n"
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	"tas0:\n"
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	"	sync\n"
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	"	isync\n"
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	: "=r" (v)
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	: "r"  (x)
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	: "cc", "memory", "r0", "r4", "r5"
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	);
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	switch(v) {
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	case 0:		return 0;
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	case 0xdeaddead: return 1;
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	default:	print("tas: corrupted 0x%lux\n", v);
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	}
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	return 0;
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}