github.com/hbdrawn/golang@v0.0.0-20141214014649-6b835209aba2/src/runtime/memmove_plan9_amd64.s (about)

     1  // Derived from Inferno's libkern/memmove-386.s (adapted for amd64)
     2  // http://code.google.com/p/inferno-os/source/browse/libkern/memmove-386.s
     3  //
     4  //         Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
     5  //         Revisions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com).  All rights reserved.
     6  //         Portions Copyright 2009 The Go Authors. All rights reserved.
     7  //
     8  // Permission is hereby granted, free of charge, to any person obtaining a copy
     9  // of this software and associated documentation files (the "Software"), to deal
    10  // in the Software without restriction, including without limitation the rights
    11  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    12  // copies of the Software, and to permit persons to whom the Software is
    13  // furnished to do so, subject to the following conditions:
    14  //
    15  // The above copyright notice and this permission notice shall be included in
    16  // all copies or substantial portions of the Software.
    17  //
    18  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    19  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    20  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
    21  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    22  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    23  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    24  // THE SOFTWARE.
    25  
    26  #include "textflag.h"
    27  
    28  // void runtime·memmove(void*, void*, uintptr)
    29  TEXT runtime·memmove(SB), NOSPLIT, $0-24
    30  
    31  	MOVQ	to+0(FP), DI
    32  	MOVQ	from+8(FP), SI
    33  	MOVQ	n+16(FP), BX
    34  
    35  	// REP instructions have a high startup cost, so we handle small sizes
    36  	// with some straightline code.  The REP MOVSQ instruction is really fast
    37  	// for large sizes.  The cutover is approximately 1K.
    38  tail:
    39  	TESTQ	BX, BX
    40  	JEQ	move_0
    41  	CMPQ	BX, $2
    42  	JBE	move_1or2
    43  	CMPQ	BX, $4
    44  	JBE	move_3or4
    45  	CMPQ	BX, $8
    46  	JBE	move_5through8
    47  	CMPQ	BX, $16
    48  	JBE	move_9through16
    49  
    50  /*
    51   * check and set for backwards
    52   */
    53  	CMPQ	SI, DI
    54  	JLS	back
    55  
    56  /*
    57   * forward copy loop
    58   */
    59  forward:
    60  	MOVQ	BX, CX
    61  	SHRQ	$3, CX
    62  	ANDQ	$7, BX
    63  
    64  	REP;	MOVSQ
    65  	JMP	tail
    66  
    67  back:
    68  /*
    69   * check overlap
    70   */
    71  	MOVQ	SI, CX
    72  	ADDQ	BX, CX
    73  	CMPQ	CX, DI
    74  	JLS	forward
    75  	
    76  /*
    77   * whole thing backwards has
    78   * adjusted addresses
    79   */
    80  	ADDQ	BX, DI
    81  	ADDQ	BX, SI
    82  	STD
    83  
    84  /*
    85   * copy
    86   */
    87  	MOVQ	BX, CX
    88  	SHRQ	$3, CX
    89  	ANDQ	$7, BX
    90  
    91  	SUBQ	$8, DI
    92  	SUBQ	$8, SI
    93  	REP;	MOVSQ
    94  
    95  	CLD
    96  	ADDQ	$8, DI
    97  	ADDQ	$8, SI
    98  	SUBQ	BX, DI
    99  	SUBQ	BX, SI
   100  	JMP	tail
   101  
   102  move_1or2:
   103  	MOVB	(SI), AX
   104  	MOVB	-1(SI)(BX*1), CX
   105  	MOVB	AX, (DI)
   106  	MOVB	CX, -1(DI)(BX*1)
   107  	RET
   108  move_0:
   109  	RET
   110  move_3or4:
   111  	MOVW	(SI), AX
   112  	MOVW	-2(SI)(BX*1), CX
   113  	MOVW	AX, (DI)
   114  	MOVW	CX, -2(DI)(BX*1)
   115  	RET
   116  move_5through8:
   117  	MOVL	(SI), AX
   118  	MOVL	-4(SI)(BX*1), CX
   119  	MOVL	AX, (DI)
   120  	MOVL	CX, -4(DI)(BX*1)
   121  	RET
   122  move_9through16:
   123  	MOVQ	(SI), AX
   124  	MOVQ	-8(SI)(BX*1), CX
   125  	MOVQ	AX, (DI)
   126  	MOVQ	CX, -8(DI)(BX*1)
   127  	RET