Text file src/pkg/math/expm1_386.s
1 // Copyright 2010 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 #include "textflag.h"
6
7 // func Expm1(x float64) float64
8 TEXT ·Expm1(SB),NOSPLIT,$0
9 FLDLN2 // F0=log(2) = 1/log2(e) ~ 0.693147
10 FMOVD x+0(FP), F0 // F0=x, F1=1/log2(e)
11 FABS // F0=|x|, F1=1/log2(e)
12 FUCOMPP F0, F1 // compare F0 to F1
13 FSTSW AX
14 SAHF
15 JCC use_exp // jump if F0 >= F1
16 FLDL2E // F0=log2(e)
17 FMULD x+0(FP), F0 // F0=x*log2(e) (-1<F0<1)
18 F2XM1 // F0=e**x-1 = 2**(x*log2(e))-1
19 FMOVDP F0, ret+8(FP)
20 RET
21 use_exp:
22 // test bits for not-finite
23 MOVL x_hi+4(FP), AX
24 ANDL $0x7ff00000, AX
25 CMPL AX, $0x7ff00000
26 JEQ not_finite
27 FLDL2E // F0=log2(e)
28 FMULD x+0(FP), F0 // F0=x*log2(e)
29 FMOVD F0, F1 // F0=x*log2(e), F1=x*log2(e)
30 FRNDINT // F0=int(x*log2(e)), F1=x*log2(e)
31 FSUBD F0, F1 // F0=int(x*log2(e)), F1=x*log2(e)-int(x*log2(e))
32 FXCHD F0, F1 // F0=x*log2(e)-int(x*log2(e)), F1=int(x*log2(e))
33 F2XM1 // F0=2**(x*log2(e)-int(x*log2(e)))-1, F1=int(x*log2(e))
34 FLD1 // F0=1, F1=2**(x*log2(e)-int(x*log2(e)))-1, F2=int(x*log2(e))
35 FADDDP F0, F1 // F0=2**(x*log2(e)-int(x*log2(e))), F1=int(x*log2(e))
36 FSCALE // F0=e**x, F1=int(x*log2(e))
37 FMOVDP F0, F1 // F0=e**x
38 FLD1 // F0=1, F1=e**x
39 FSUBDP F0, F1 // F0=e**x-1
40 FMOVDP F0, ret+8(FP)
41 RET
42 not_finite:
43 // test bits for -Inf
44 MOVL x_hi+4(FP), BX
45 MOVL x_lo+0(FP), CX
46 CMPL BX, $0xfff00000
47 JNE not_neginf
48 CMPL CX, $0
49 JNE not_neginf
50 FLD1 // F0=1
51 FCHS // F0=-1
52 FMOVDP F0, ret+8(FP)
53 RET
54 not_neginf:
55 MOVL CX, ret_lo+8(FP)
56 MOVL BX, ret_hi+12(FP)
57 RET
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