MOVQ a_len+8(FP), DX
	MOVQ b_base+24(FP), R8
	MOVQ b_len+32(FP), AX
	MOVQ DI, R10
	LEAQ ret+48(FP), R11
	JMP  indexbody<>(SB)

TEXT ·IndexString(SB),NOSPLIT,$0-40
	MOVQ a_base+0(FP), DI
	MOVQ a_len+8(FP), DX
	MOVQ b_base+16(FP), R8
	MOVQ b_len+24(FP), AX
	MOVQ DI, R10
	LEAQ ret+32(FP), R11
	JMP  indexbody<>(SB)

// AX: length of string, that we are searching for
// DX: length of string, in which we are searching