src/pkg/runtime/amd64/memmove.s

// Derived from Inferno's libkern/memmove-386.s (adapted for amd64)
// http://code.google.com/p/inferno-os/source/browse/libkern/memmove-386.s
//
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//
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TEXT runtime·memmove(SB), 7, $0

	MOVQ	to+0(FP), DI
	MOVQ	fr+8(FP), SI
	MOVLQSX	n+16(FP), BX
	CMPQ	BX, $0
	JLT	fault

/*
 * check and set for backwards
 */
	CMPQ	SI, DI
	JLS	back

/*
 * forward copy loop
 */
forward:	
	MOVQ	BX, CX
	SHRQ	$3, CX
	ANDQ	$7, BX

	REP;	MOVSQ
	MOVQ	BX, CX
	REP;	MOVSB

	MOVQ	to+0(FP),AX
	RET
back:
/*
 * check overlap
 */
	MOVQ	SI, CX
	ADDQ	BX, CX
	CMPQ	CX, DI
	JLS	forward
	
/*
 * whole thing backwards has
 * adjusted addresses
 */
	ADDQ	BX, DI
	ADDQ	BX, SI
	STD

/*
 * copy
 */
	MOVQ	BX, CX
	SHRQ	$3, CX
	ANDQ	$7, BX

	SUBQ	$8, DI
	SUBQ	$8, SI
	REP;	MOVSQ

	ADDQ	$7, DI
	ADDQ	$7, SI
	MOVQ	BX, CX
	REP;	MOVSB

	CLD
	MOVQ	to+0(FP),AX
	RET

/*
 * if called with negative count,
 * treat as error rather than
 * rotating all of memory
 */
fault:
	MOVQ	$0,SI
	MOVQ	0(SI), AX
	RET