diff options
Diffstat (limited to 'src/math/exp_amd64.s')
| -rw-r--r-- | src/math/exp_amd64.s | 114 |
1 files changed, 114 insertions, 0 deletions
diff --git a/src/math/exp_amd64.s b/src/math/exp_amd64.s new file mode 100644 index 000000000..d9cf8fd86 --- /dev/null +++ b/src/math/exp_amd64.s @@ -0,0 +1,114 @@ +// 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 "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 |