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	1	/*
	2	* Copyright (c) 2010 Apple Inc. All rights reserved.
	3	*
	4	* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
	5	*
	6	* This file contains Original Code and/or Modifications of Original Code
	7	* as defined in and that are subject to the Apple Public Source License
	8	* Version 2.0 (the 'License'). You may not use this file except in
	9	* compliance with the License. The rights granted to you under the License
	10	* may not be used to create, or enable the creation or redistribution of,
	11	* unlawful or unlicensed copies of an Apple operating system, or to
	12	* circumvent, violate, or enable the circumvention or violation of, any
	13	* terms of an Apple operating system software license agreement.
	14	*
	15	* Please obtain a copy of the License at
	16	* http://www.opensource.apple.com/apsl/ and read it before using this file.
	17	*
	18	* The Original Code and all software distributed under the License are
	19	* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
	20	* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
	21	* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
	22	* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
	23	* Please see the License for the specific language governing rights and
	24	* limitations under the License.
	25	*
	26	* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
	27	*/
	28	/*
	29	* @OSF_COPYRIGHT@
	30	*/
	31	/*
	32	* @APPLE_FREE_COPYRIGHT@
	33	*/
	34	/*
	35	* File: rtclock_asm_native.h
	36	* Purpose: Native routines for reading nanotime
	37	*/
	38
	39	#ifndef _PAL_RTCLOCK_ASM_NATIVE_H_
	40	#define _PAL_RTCLOCK_ASM_NATIVE_H_
	41
	42
	43	#if defined(__i386__)
	44	/*
	45	* Assembly snippet included in exception handlers and rtc_nanotime_read()
	46	* %edi points to nanotime info struct
	47	* %edx:%eax returns nanotime
	48	*/
	49	#define PAL_RTC_NANOTIME_READ_FAST() \
	50	0: movl RNT_GENERATION(%edi),%esi /* being updated? */ ; \
	51	testl %esi,%esi ; \
	52	jz 0b /* wait until done */ ; \
	53	lfence ; \
	54	rdtsc ; \
	55	lfence ; \
	56	subl RNT_TSC_BASE(%edi),%eax ; \
	57	sbbl RNT_TSC_BASE+4(%edi),%edx /* tsc - tsc_base */ ; \
	58	movl RNT_SCALE(%edi),%ecx /* * scale factor */ ; \
	59	movl %edx,%ebx ; \
	60	mull %ecx ; \
	61	movl %ebx,%eax ; \
	62	movl %edx,%ebx ; \
	63	mull %ecx ; \
	64	addl %ebx,%eax ; \
	65	adcl $0,%edx ; \
	66	addl RNT_NS_BASE(%edi),%eax /* + ns_base */ ; \
	67	adcl RNT_NS_BASE+4(%edi),%edx ; \
	68	cmpl RNT_GENERATION(%edi),%esi /* check for update */ ; \
	69	jne 0b /* do it all again */
	70
	71	#elif defined(__x86_64__)
	72
	73	/*
	74	* Assembly snippet included in exception handlers and rtc_nanotime_read()
	75	*
	76	*
	77	* Warning! There are several copies of this code in the trampolines found in
	78	* osfmk/x86_64/idt64.s, coming from the various TIMER macros in rtclock_asm.h.
	79	* They're all kept in sync by using the RTC_NANOTIME_READ() macro.
	80	*
	81	* The algorithm we use is:
	82	*
	83	* ns = ((((rdtsc - rnt_tsc_base)<<rnt_shift)rnt_tsc_scale) / 2*32) + rnt_ns_base;
	84	*
	85	* rnt_shift, a constant computed during initialization, is the smallest value for which:
	86	*
	87	* (tscFreq << rnt_shift) > SLOW_TSC_THRESHOLD
	88	*
	89	* Where SLOW_TSC_THRESHOLD is about 10e9. Since most processor's tscFreqs are greater
	90	* than 1GHz, rnt_shift is usually 0. rnt_tsc_scale is also a 32-bit constant:
	91	*
	92	* rnt_tsc_scale = (10e9 * 2**32) / (tscFreq << rnt_shift);
	93	*
	94	* %rdi points to nanotime info struct.
	95	* %rax returns nanotime
	96	*/
	97	#define PAL_RTC_NANOTIME_READ_FAST() \
	98	0: movl RNT_GENERATION(%rdi),%esi ; \
	99	test %esi,%esi /* info updating? */ ; \
	100	jz 0b /* - wait if so */ ; \
	101	lfence ; \
	102	rdtsc ; \
	103	lfence ; \
	104	shlq $32,%rdx ; \
	105	movl RNT_SHIFT(%rdi),%ecx ; \
	106	orq %rdx,%rax /* %rax := tsc */ ; \
	107	subq RNT_TSC_BASE(%rdi),%rax /* tsc - tsc_base */ ; \
	108	shlq %cl,%rax ; \
	109	movl RNT_SCALE(%rdi),%ecx ; \
	110	mulq %rcx /* delta * scale */ ; \
	111	shrdq $32,%rdx,%rax /* %rdx:%rax >>= 32 */ ; \
	112	addq RNT_NS_BASE(%rdi),%rax /* add ns_base */ ; \
	113	cmpl RNT_GENERATION(%rdi),%esi /* repeat if changed */ ; \
	114	jne 0b
	115
	116	#endif /* !defined(x86_64) */
	117
	118
	119	#endif /* _PAL_RTCLOCK_ASM_NATIVE_H_ */