// Copyright ©2015 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
// Some of the loop unrolling code is copied from:
// http://golang.org/src/math/big/arith_amd64.s
// which is distributed under these terms:
//
// Copyright (c) 2012 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
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//+build !noasm,!appengine

#include "textflag.h"

#define X_PTR SI
#define Y_PTR DI
#define DST_PTR DI
#define IDX AX
#define LEN CX
#define TAIL BX
#define INC_X R8
#define INCx3_X R11
#define INC_Y R9
#define INCx3_Y R12
#define INC_DST R9
#define INCx3_DST R12
#define ALPHA X0
#define ALPHA_2 X1

// func AxpyInc(alpha float64, x, y []float64, n, incX, incY, ix, iy uintptr)
TEXT ·AxpyInc(SB), NOSPLIT, $0
	MOVQ x_base+8(FP), X_PTR  // X_PTR = &x
	MOVQ y_base+32(FP), Y_PTR // Y_PTR = &y
	MOVQ n+56(FP), LEN        // LEN = n
	CMPQ LEN, $0              // if LEN == 0 { return }
	JE   end

	MOVQ ix+80(FP), INC_X
	MOVQ iy+88(FP), INC_Y
	LEAQ (X_PTR)(INC_X*8), X_PTR // X_PTR = &(x[ix])
	LEAQ (Y_PTR)(INC_Y*8), Y_PTR // Y_PTR = &(y[iy])
	MOVQ Y_PTR, DST_PTR          // DST_PTR = Y_PTR  // Write pointer

	MOVQ incX+64(FP), INC_X // INC_X = incX * sizeof(float64)
	SHLQ $3, INC_X
	MOVQ incY+72(FP), INC_Y // INC_Y = incY * sizeof(float64)
	SHLQ $3, INC_Y

	MOVSD alpha+0(FP), ALPHA // ALPHA = alpha
	MOVQ  LEN, TAIL
	ANDQ  $3, TAIL           // TAIL = n % 4
	SHRQ  $2, LEN            // LEN = floor( n / 4 )
	JZ    tail_start         // if LEN == 0 { goto tail_start }

	MOVAPS ALPHA, ALPHA_2            // ALPHA_2 = ALPHA  for pipelining
	LEAQ   (INC_X)(INC_X*2), INCx3_X // INCx3_X = INC_X * 3
	LEAQ   (INC_Y)(INC_Y*2), INCx3_Y // INCx3_Y = INC_Y * 3

loop:  // do {  // y[i] += alpha * x[i] unrolled 4x.
	MOVSD (X_PTR), X2            // X_i = x[i]
	MOVSD (X_PTR)(INC_X*1), X3
	MOVSD (X_PTR)(INC_X*2), X4
	MOVSD (X_PTR)(INCx3_X*1), X5

	MULSD ALPHA, X2   // X_i *= a
	MULSD ALPHA_2, X3
	MULSD ALPHA, X4
	MULSD ALPHA_2, X5

	ADDSD (Y_PTR), X2            // X_i += y[i]
	ADDSD (Y_PTR)(INC_Y*1), X3
	ADDSD (Y_PTR)(INC_Y*2), X4
	ADDSD (Y_PTR)(INCx3_Y*1), X5

	MOVSD X2, (DST_PTR)              // y[i] = X_i
	MOVSD X3, (DST_PTR)(INC_DST*1)
	MOVSD X4, (DST_PTR)(INC_DST*2)
	MOVSD X5, (DST_PTR)(INCx3_DST*1)

	LEAQ (X_PTR)(INC_X*4), X_PTR // X_PTR = &(X_PTR[incX*4])
	LEAQ (Y_PTR)(INC_Y*4), Y_PTR // Y_PTR = &(Y_PTR[incY*4])
	DECQ LEN
	JNZ  loop                    // } while --LEN > 0
	CMPQ TAIL, $0                // if TAIL == 0 { return }
	JE   end

tail_start: // Reset Loop registers
	MOVQ TAIL, LEN // Loop counter: LEN = TAIL
	SHRQ $1, LEN   // LEN = floor( LEN / 2 )
	JZ   tail_one

tail_two:
	MOVSD (X_PTR), X2              // X_i = x[i]
	MOVSD (X_PTR)(INC_X*1), X3
	MULSD ALPHA, X2                // X_i *= a
	MULSD ALPHA, X3
	ADDSD (Y_PTR), X2              // X_i += y[i]
	ADDSD (Y_PTR)(INC_Y*1), X3
	MOVSD X2, (DST_PTR)            // y[i] = X_i
	MOVSD X3, (DST_PTR)(INC_DST*1)

	LEAQ (X_PTR)(INC_X*2), X_PTR // X_PTR = &(X_PTR[incX*2])
	LEAQ (Y_PTR)(INC_Y*2), Y_PTR // Y_PTR = &(Y_PTR[incY*2])

	ANDQ $1, TAIL
	JZ   end      // if TAIL == 0 { goto end }

tail_one:
	// y[i] += alpha * x[i] for the last n % 4 iterations.
	MOVSD (X_PTR), X2   // X2 = x[i]
	MULSD ALPHA, X2     // X2 *= a
	ADDSD (Y_PTR), X2   // X2 += y[i]
	MOVSD X2, (DST_PTR) // y[i] = X2

end:
	RET