// [0]P is the point at infinity and it's not stored.
type p256Table [16]P256Point

// p256Select sets res to the point at index idx in the table.
// idx must be in [0, 15]. It executes in constant time.
//
//go:noescape
func p256Select(res *P256Point, table *p256Table, idx int)

// p256AffinePoint is a point in affine coordinates (x, y). x and y are still

	CSEL	CS, t3, acc3, acc3

	STP	(acc0, acc1), 0*16(res_ptr)
	STP	(acc2, acc3), 1*16(res_ptr)

	RET
/* ---------------------------------------*/
// func p256Select(res *P256Point, table *p256Table, idx int)
TEXT ·p256Select(SB),NOSPLIT,$0
	MOVD	idx+16(FP), const0
	MOVD	table+8(FP), b_ptr
	MOVD	res+0(FP), res_ptr

	EOR	x0, x0, x0
	EOR	x1, x1, x1
	EOR	x2, x2, x2
	EOR	x3, x3, x3

	MOVQ acc4, (8*0)(res_ptr)
	MOVQ acc5, (8*1)(res_ptr)
	MOVQ acc0, (8*2)(res_ptr)
	MOVQ acc1, (8*3)(res_ptr)

	RET
/* ---------------------------------------*/
// func p256Select(res *P256Point, table *p256Table, idx int)
TEXT ·p256Select(SB),NOSPLIT,$0
	MOVQ idx+16(FP),AX
	MOVQ table+8(FP),DI
	MOVQ res+0(FP),DX

	PXOR X15, X15	// X15 = 0
	PCMPEQL X14, X14 // X14 = -1
	PSUBL X14, X15   // X15 = 1

#define Y2L    V8
#define Y2H    V9
#define Z2L    V10
#define Z2H    V11

#define ONE   V18
#define IDX   V19
#define SEL1  V20
#define SEL2  V21
// func p256Select(point *p256Point, table *p256Table, idx int)
TEXT ·p256Select(SB), NOSPLIT, $0-24
	MOVD res+0(FP), P3ptr
	MOVD table+8(FP), P1ptr
	MOVD $16, R16
	MOVD $32, R17
	MOVD $48, R18
	MOVD $64, R19
	MOVD $80, R20

#undef Z2H
#undef ZER
#undef SEL1

// ---------------------------------------
// Constant time table access
// Indexed from 1 to 15, with -1 offset
// (index 0 is implicitly point at infinity)
// func p256Select(res *P256Point, table *p256Table, idx int)
#define P3ptr   R1
#define P1ptr   R2
#define COUNT   R4

#define X1L    V0
#define X1H    V1
#define Y1L    V2
#define Y1H    V3
#define Z1L    V4