text: // Copyright ©2016 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,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // 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
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  //+build !noasm,!appengine,!safe
  
  #include "textflag.h"
  
  #define MOVDDUP_ALPHA    LONG $0x44120FF2; WORD $0x2024 // @ MOVDDUP 32(SP), X0  /*XMM0, 32[RSP]*/
  
  #define X_PTR SI
  #define DST_PTR DI
  #define IDX AX
  #define LEN CX
  #define TAIL BX
  #define ALPHA X0
  #define ALPHA_2 X1
  
  // func ScalUnitaryTo(dst []float64, alpha float64, x []float64)
  // This function assumes len(dst) >= len(x).
  TEXT ·ScalUnitaryTo(SB), NOSPLIT, $0
  	MOVQ x_base+32(FP), X_PTR    // X_PTR = &x
  	MOVQ dst_base+0(FP), DST_PTR // DST_PTR = &dst
  	MOVDDUP_ALPHA                // ALPHA = { alpha, alpha }
  	MOVQ x_len+40(FP), LEN       // LEN = len(x)
  	CMPQ LEN, $0
  	JE   end                     // if LEN == 0 { return }
  
  	XORQ IDX, IDX   // IDX = 0
  	MOVQ LEN, TAIL
  	ANDQ $7, TAIL   // TAIL = LEN % 8
  	SHRQ $3, LEN    // LEN = floor( LEN / 8 )
  	JZ   tail_start // if LEN == 0 { goto tail_start }
  
  	MOVUPS ALPHA, ALPHA_2 // ALPHA_2 = ALPHA for pipelining
  
  loop:  // do { // dst[i] = alpha * x[i] unrolled 8x.
  	MOVUPS (X_PTR)(IDX*8), X2   // X_i = x[i]
  	MOVUPS 16(X_PTR)(IDX*8), X3
  	MOVUPS 32(X_PTR)(IDX*8), X4
  	MOVUPS 48(X_PTR)(IDX*8), X5
  
  	MULPD ALPHA, X2   // X_i *= ALPHA
  	MULPD ALPHA_2, X3
  	MULPD ALPHA, X4
  	MULPD ALPHA_2, X5
  
  	MOVUPS X2, (DST_PTR)(IDX*8)   // dst[i] = X_i
  	MOVUPS X3, 16(DST_PTR)(IDX*8)
  	MOVUPS X4, 32(DST_PTR)(IDX*8)
  	MOVUPS X5, 48(DST_PTR)(IDX*8)
  
  	ADDQ $8, IDX  // i += 8
  	DECQ LEN
  	JNZ  loop     // while --LEN > 0
  	CMPQ TAIL, $0
  	JE   end      // if TAIL == 0 { return }
  
  tail_start: // Reset loop counters
  	MOVQ TAIL, LEN // Loop counter: LEN = TAIL
  	SHRQ $1, LEN   // LEN = floor( TAIL / 2 )
  	JZ   tail_one  // if LEN == 0 { goto tail_one }
  
  tail_two: // do {
  	MOVUPS (X_PTR)(IDX*8), X2   // X_i = x[i]
  	MULPD  ALPHA, X2            // X_i *= ALPHA
  	MOVUPS X2, (DST_PTR)(IDX*8) // dst[i] = X_i
  	ADDQ   $2, IDX              // i += 2
  	DECQ   LEN
  	JNZ    tail_two             // while --LEN > 0
  
  	ANDQ $1, TAIL
  	JZ   end      // if TAIL == 0 { return }
  
  tail_one:
  	MOVSD (X_PTR)(IDX*8), X2   // X_i = x[i]
  	MULSD ALPHA, X2            // X_i *= ALPHA
  	MOVSD X2, (DST_PTR)(IDX*8) // dst[i] = X_i
  
  end:
  	RET
  