| // 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. |
| |
| // func Expm1(x float64) float64 |
| TEXT ·Expm1(SB),7,$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, r+8(FP) |
| RET |
| use_exp: |
| // test bits for not-finite |
| MOVL x+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, r+8(FP) |
| RET |
| not_finite: |
| // test bits for -Inf |
| MOVL x+4(FP), BX |
| MOVL x+0(FP), CX |
| CMPL BX, $0xfff00000 |
| JNE not_neginf |
| CMPL CX, $0 |
| JNE not_neginf |
| FLD1 // F0=1 |
| FCHS // F0=-1 |
| FMOVDP F0, r+8(FP) |
| RET |
| not_neginf: |
| MOVL CX, r+8(FP) |
| MOVL BX, r+12(FP) |
| RET |
