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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 "../../cmd/ld/textflag.h"
// func Expm1(x float64) float64
TEXT ·Expm1(SB),NOSPLIT,$0
FLDLN2 // F0=log(2) = 1/log2(e) ~ 0.693147
FMOVD x+0(FP), F0 // F0=x, F1=1/log2(e)
FABS // F0=|x|, F1=1/log2(e)
FUCOMPP F0, F1 // compare F0 to F1
FSTSW AX
SAHF
JCC use_exp // jump if F0 >= F1
FLDL2E // F0=log2(e)
FMULD x+0(FP), F0 // F0=x*log2(e) (-1<F0<1)
F2XM1 // F0=e**x-1 = 2**(x*log2(e))-1
FMOVDP F0, ret+8(FP)
RET
use_exp:
// test bits for not-finite
MOVL x_hi+4(FP), AX
ANDL $0x7ff00000, AX
CMPL AX, $0x7ff00000
JEQ not_finite
FLDL2E // F0=log2(e)
FMULD x+0(FP), F0 // F0=x*log2(e)
FMOVD F0, F1 // F0=x*log2(e), F1=x*log2(e)
FRNDINT // F0=int(x*log2(e)), F1=x*log2(e)
FSUBD F0, F1 // F0=int(x*log2(e)), F1=x*log2(e)-int(x*log2(e))
FXCHD F0, F1 // F0=x*log2(e)-int(x*log2(e)), F1=int(x*log2(e))
F2XM1 // F0=2**(x*log2(e)-int(x*log2(e)))-1, F1=int(x*log2(e))
FLD1 // F0=1, F1=2**(x*log2(e)-int(x*log2(e)))-1, F2=int(x*log2(e))
FADDDP F0, F1 // F0=2**(x*log2(e)-int(x*log2(e))), F1=int(x*log2(e))
FSCALE // F0=e**x, F1=int(x*log2(e))
FMOVDP F0, F1 // F0=e**x
FLD1 // F0=1, F1=e**x
FSUBDP F0, F1 // F0=e**x-1
FMOVDP F0, ret+8(FP)
RET
not_finite:
// test bits for -Inf
MOVL x_hi+4(FP), BX
MOVL x_lo+0(FP), CX
CMPL BX, $0xfff00000
JNE not_neginf
CMPL CX, $0
JNE not_neginf
FLD1 // F0=1
FCHS // F0=-1
FMOVDP F0, ret+8(FP)
RET
not_neginf:
MOVL CX, ret_lo+8(FP)
MOVL BX, ret_hi+12(FP)
RET
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