// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "../../cmd/ld/textflag.h"
// The method is based on a paper by Naoki Shibata: "Efficient evaluation
// methods of elementary functions suitable for SIMD computation", Proc.
// of International Supercomputing Conference 2010 (ISC'10), pp. 25 -- 32
// (May 2010). The paper is available at
// http://www.springerlink.com/content/340228x165742104/
//
// The original code and the constants below are from the author's
// implementation available at http://freshmeat.net/projects/sleef.
// The README file says, "The software is in public domain.
// You can use the software without any obligation."
//
// This code is a simplified version of the original.
#define LN2 0.6931471805599453094172321214581766 // log_e(2)
#define LOG2E 1.4426950408889634073599246810018920 // 1/LN2
#define LN2U 0.69314718055966295651160180568695068359375 // upper half LN2
#define LN2L 0.28235290563031577122588448175013436025525412068e-12 // lower half LN2
#define T0 1.0
#define T1 0.5
#define T2 1.6666666666666666667e-1
#define T3 4.1666666666666666667e-2
#define T4 8.3333333333333333333e-3
#define T5 1.3888888888888888889e-3
#define T6 1.9841269841269841270e-4
#define T7 2.4801587301587301587e-5
#define PosInf 0x7FF0000000000000
#define NegInf 0xFFF0000000000000
// func Exp(x float64) float64
TEXT ·Exp(SB),NOSPLIT,$0
// test bits for not-finite
MOVQ x+0(FP), BX
MOVQ $~(1<<63), AX // sign bit mask
MOVQ BX, DX
ANDQ AX, DX
MOVQ $PosInf, AX
CMPQ AX, DX
JLE notFinite
MOVQ BX, X0
MOVSD $LOG2E, X1
MULSD X0, X1
CVTSD2SL X1, BX // BX = exponent
CVTSL2SD BX, X1
MOVSD $LN2U, X2
MULSD X1, X2
SUBSD X2, X0
MOVSD $LN2L, X2
MULSD X1, X2
SUBSD X2, X0
// reduce argument
MULSD $0.0625, X0
// Taylor series evaluation
MOVSD $T7, X1
MULSD X0, X1
ADDSD $T6, X1
MULSD X0, X1
ADDSD $T5, X1
MULSD X0, X1
ADDSD $T4, X1
MULSD X0, X1
ADDSD $T3, X1
MULSD X0, X1
ADDSD $T2, X1
MULSD X0, X1
ADDSD $T1, X1
MULSD X0, X1
ADDSD $T0, X1
MULSD X1, X0
MOVSD $2.0, X1
ADDSD X0, X1
MULSD X1, X0
MOVSD $2.0, X1
ADDSD X0, X1
MULSD X1, X0
MOVSD $2.0, X1
ADDSD X0, X1
MULSD X1, X0
MOVSD $2.0, X1
ADDSD X0, X1
MULSD X1, X0
ADDSD $1.0, X0
// return fr * 2**exponent
MOVL $0x3FF, AX // bias
ADDL AX, BX
JLE underflow
CMPL BX, $0x7FF
JGE overflow
MOVL $52, CX
SHLQ CX, BX
MOVQ BX, X1
MULSD X1, X0
MOVSD X0, ret+8(FP)
RET
notFinite:
// test bits for -Inf
MOVQ $NegInf, AX
CMPQ AX, BX
JNE notNegInf
// -Inf, return 0
underflow: // return 0
MOVQ $0, AX
MOVQ AX, ret+8(FP)
RET
overflow: // return +Inf
MOVQ $PosInf, BX
notNegInf: // NaN or +Inf, return x
MOVQ BX, ret+8(FP)
RET