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 58
