github.com/hikaru7719/go@v0.0.0-20181025140707-c8b2ac68906a/src/runtime/memmove_amd64p32.s (about)

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  #include "textflag.h"
     6  
     7  // This could use MOVSQ, but we use MOVSL so that if an object ends in
     8  // a 4 byte pointer, we copy it as a unit instead of byte by byte.
     9  
    10  // func memmove(to, from unsafe.Pointer, n uintptr)
    11  TEXT runtime·memmove(SB), NOSPLIT, $0-12
    12  	MOVL	to+0(FP), DI
    13  	MOVL	from+4(FP), SI
    14  	MOVL	n+8(FP), BX
    15  
    16  	CMPL	SI, DI
    17  	JLS back
    18  
    19  forward:
    20  	MOVL	BX, CX
    21  	SHRL	$2, CX
    22  	ANDL	$3, BX
    23  	REP; MOVSL
    24  	MOVL	BX, CX
    25  	REP; MOVSB
    26  	RET
    27  
    28  back:
    29  	MOVL	SI, CX
    30  	ADDL	BX, CX
    31  	CMPL	CX, DI
    32  	JLS forward
    33  
    34  	ADDL	BX, DI
    35  	ADDL	BX, SI
    36  	STD
    37  
    38  	MOVL	BX, CX
    39  	SHRL	$2, CX
    40  	ANDL	$3, BX
    41  	SUBL	$4, DI
    42  	SUBL	$4, SI
    43  	REP; MOVSL
    44  	ADDL	$3, DI
    45  	ADDL	$3, SI
    46  	MOVL	BX, CX
    47  	REP; MOVSB
    48  	CLD
    49  
    50  	// Note: we copy only 4 bytes at a time so that the tail is at most
    51  	// 3 bytes. That guarantees that we aren't copying pointers with MOVSB.
    52  	// See issue 13160.
    53  	RET