// 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.
//    * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

//+build !noasm,!appengine,!safe

#include "textflag.h"

#define X_PTR SI
#define Y_PTR DI
#define DST_PTR DX
#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 R10
#define INCx3_DST R13
#define ALPHA X0
#define ALPHA_2 X1

// func AxpyIncTo(dst []float64, incDst, idst uintptr, alpha float64, x, y []float64, n, incX, incY, ix, iy uintptr)
TEXT ·AxpyIncTo(SB), NOSPLIT, $0
	MOVQ dst_base+0(FP), DST_PTR // DST_PTR := &dst
	MOVQ x_base+48(FP), X_PTR    // X_PTR := &x
	MOVQ y_base+72(FP), Y_PTR    // Y_PTR := &y
	MOVQ n+96(FP), LEN           // LEN := n
	CMPQ LEN, $0                 // if LEN == 0 { return }
	JE   end

	MOVQ ix+120(FP), INC_X
	LEAQ (X_PTR)(INC_X*8), X_PTR       // X_PTR = &(x[ix])
	MOVQ iy+128(FP), INC_Y
	LEAQ (Y_PTR)(INC_Y*8), Y_PTR       // Y_PTR = &(dst[idst])
	MOVQ idst+32(FP), INC_DST
	LEAQ (DST_PTR)(INC_DST*8), DST_PTR // DST_PTR = &(y[iy])

	MOVQ  incX+104(FP), INC_X    // INC_X = incX * sizeof(float64)
	SHLQ  $3, INC_X
	MOVQ  incY+112(FP), INC_Y    // INC_Y = incY * sizeof(float64)
	SHLQ  $3, INC_Y
	MOVQ  incDst+24(FP), INC_DST // INC_DST = incDst * sizeof(float64)
	SHLQ  $3, INC_DST
	MOVSD alpha+40(FP), 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 }

	MOVSD 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
	LEAQ  (INC_DST)(INC_DST*2), INCx3_DST // INCx3_DST = INC_DST * 3

loop:  // do {  // y[i] += alpha * x[i] unrolled 2x.
	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])
	LEAQ (DST_PTR)(INC_DST*4), DST_PTR // DST_PTR = &(DST_PTR[incDst*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])
	LEAQ (DST_PTR)(INC_DST*2), DST_PTR // DST_PTR = &(DST_PTR[incY*2]

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

tail_one:
	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
