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// 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.
// +build !noasm,!gccgo,!safe
#include "textflag.h"
// func L1Norm(x []float64) float64
TEXT ·L1Norm(SB), NOSPLIT, $0
MOVQ x_base+0(FP), SI // SI = &x
MOVQ x_len+8(FP), CX // CX = len(x)
XORQ AX, AX // i = 0
PXOR X0, X0 // p_sum_i = 0
PXOR X1, X1
PXOR X2, X2
PXOR X3, X3
PXOR X4, X4
PXOR X5, X5
PXOR X6, X6
PXOR X7, X7
CMPQ CX, $0 // if CX == 0 { return 0 }
JE absum_end
MOVQ CX, BX
ANDQ $7, BX // BX = len(x) % 8
SHRQ $3, CX // CX = floor( len(x) / 8 )
JZ absum_tail_start // if CX == 0 { goto absum_tail_start }
absum_loop: // do {
// p_sum += max( p_sum + x[i], p_sum - x[i] )
MOVUPS (SI)(AX*8), X8 // X_i = x[i:i+1]
MOVUPS 16(SI)(AX*8), X9
MOVUPS 32(SI)(AX*8), X10
MOVUPS 48(SI)(AX*8), X11
ADDPD X8, X0 // p_sum_i += X_i ( positive values )
ADDPD X9, X2
ADDPD X10, X4
ADDPD X11, X6
SUBPD X8, X1 // p_sum_(i+1) -= X_i ( negative values )
SUBPD X9, X3
SUBPD X10, X5
SUBPD X11, X7
MAXPD X1, X0 // p_sum_i = max( p_sum_i, p_sum_(i+1) )
MAXPD X3, X2
MAXPD X5, X4
MAXPD X7, X6
MOVAPS X0, X1 // p_sum_(i+1) = p_sum_i
MOVAPS X2, X3
MOVAPS X4, X5
MOVAPS X6, X7
ADDQ $8, AX // i += 8
LOOP absum_loop // } while --CX > 0
// p_sum_0 = \sum_{i=1}^{3}( p_sum_(i*2) )
ADDPD X3, X0
ADDPD X5, X7
ADDPD X7, X0
// p_sum_0[0] = p_sum_0[0] + p_sum_0[1]
MOVAPS X0, X1
SHUFPD $0x3, X0, X0 // lower( p_sum_0 ) = upper( p_sum_0 )
ADDSD X1, X0
CMPQ BX, $0
JE absum_end // if BX == 0 { goto absum_end }
absum_tail_start: // Reset loop registers
MOVQ BX, CX // Loop counter: CX = BX
XORPS X8, X8 // X_8 = 0
absum_tail: // do {
// p_sum += max( p_sum + x[i], p_sum - x[i] )
MOVSD (SI)(AX*8), X8 // X_8 = x[i]
MOVSD X0, X1 // p_sum_1 = p_sum_0
ADDSD X8, X0 // p_sum_0 += X_8
SUBSD X8, X1 // p_sum_1 -= X_8
MAXSD X1, X0 // p_sum_0 = max( p_sum_0, p_sum_1 )
INCQ AX // i++
LOOP absum_tail // } while --CX > 0
absum_end: // return p_sum_0
MOVSD X0, sum+24(FP)
RET
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