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// 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"
// func Log1p(x float64) float64
TEXT ·Log1p(SB),NOSPLIT,$0
FMOVD $(2.928932188134524e-01), F0
FMOVD x+0(FP), F0 // F0=x, F1=1-sqrt(2)/2 = 0.29289321881345247559915564
FABS // F0=|x|, F1=1-sqrt(2)/2
FUCOMPP F0, F1 // compare F0 to F1
FSTSW AX
FLDLN2 // F0=log(2)
ANDW $0x0100, AX
JEQ use_fyl2x // jump if F0 >= F1
FMOVD x+0(FP), F0 // F0=x, F1=log(2)
FYL2XP1 // F0=log(1+x)=log2(1+x)*log(2)
FMOVDP F0, ret+8(FP)
RET
use_fyl2x:
FLD1 // F0=1, F2=log(2)
FADDD x+0(FP), F0 // F0=1+x, F1=log(2)
FYL2X // F0=log(1+x)=log2(1+x)*log(2)
FMOVDP F0, ret+8(FP)
RET
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