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Shorter i386 Exp().

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Rika Ichinose 2024-02-16 01:58:34 +03:00 committed by FPK
parent 240739e71d
commit e42209457e
1 changed files with 31 additions and 54 deletions
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85
rtl/i386/math.inc
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@ -197,7 +197,7 @@ const
end;
{$ifdef OLD_ASSEMBLER}
{$if not defined(FPC_PIC) or defined(OLD_ASSEMBLER)}
{$define DISABLE_PIC_IN_EXP_REAL}
{$endif}
{$define FPC_SYSTEM_HAS_EXP}
@ -205,11 +205,11 @@ const
* translated into AT&T syntax
+ PIC support
* return +Inf/0 for +Inf/-Inf input, instead of NaN }
function fpc_exp_real(d : ValReal) : ValReal;assembler;compilerproc;
function fpc_exp_real(d : ValReal) : ValReal;assembler;nostackframe;compilerproc;
{ [esp + 4 .. esp + 13] = d }
const
ln2hi: double=6.9314718036912382E-001;
ln2lo: double=1.9082149292705877E-010;
large: single=24576.0;
two: single=2.0;
half: single=0.5;
asm
@ -218,23 +218,15 @@ const
.LPIC:
pop %ecx
{$endif not DISABLE_PIC_IN_EXP_REAL}
fldt d
fldt 4(%esp)
fldl2e
fmul %st(1),%st { z = d * log2(e) }
frndint
{ Calculate frac(z) using modular arithmetic to avoid precision loss. }
{$ifndef DISABLE_PIC_IN_EXP_REAL}
fldl ln2hi-.LPIC(%ecx)
{$else}
fldl ln2hi
{$endif}
fldl ln2hi{$ifndef DISABLE_PIC_IN_EXP_REAL}-.LPIC(%ecx){$endif}
fmul %st(1),%st
fsubrp %st,%st(2)
{$ifndef DISABLE_PIC_IN_EXP_REAL}
fldl ln2lo-.LPIC(%ecx)
{$else}
fldl ln2lo
{$endif}
fldl ln2lo{$ifndef DISABLE_PIC_IN_EXP_REAL}-.LPIC(%ecx){$endif}
fmul %st(1),%st
fsubrp %st,%st(2)
fxch %st(1) { (d-int(z)*ln2_hi)-int(z)*ln2_lo }
@ -244,51 +236,36 @@ const
{ The above code can result in |frac(z)|>1, particularly when rounding mode
is not "round to nearest". f2xm1 is undefined in this case, so a check
is necessary. Furthermore, frac(z) evaluates to NaN for d=+-Inf. }
fld %st
fabs
fld1
fcompp
fstsw %ax
sahf
jp .L3 { NaN }
jae .L1 { frac(z) <= 1 }
fld %st(1)
fabs
{$ifndef DISABLE_PIC_IN_EXP_REAL}
fcomps large-.LPIC(%ecx)
{$else}
fcomps large
{$endif}
fstsw %ax
sahf
jb .L0 { int(z) < 24576 }
.L3:
fstp %st { zero out frac(z), hard way because }
fldz { "fsub %st,%st" does not work for NaN }
jmp .L1
.L0:
{ Calculate 2**frac(z)-1 as N*(N+2), where N=2**(frac(z)/2)-1 }
{$ifndef DISABLE_PIC_IN_EXP_REAL}
fmuls half-.LPIC(%ecx)
{$else}
fmuls half
{$endif}
fsts 4(%esp) { Save frac(z) as single. Usually a lot faster than saving 80-bit extended. }
mov 4(%esp), %eax
shr $23, %eax
movzbl %al, %eax
sub $127, %eax { eax = single(frac(z)) exponent. If < 0, |frac(z)| < 1. }
jae .LFracOutOfRange
f2xm1
fld %st
{$ifndef DISABLE_PIC_IN_EXP_REAL}
fadds two-.LPIC(%ecx)
{$else}
fadds two
{$endif}
fmulp %st,%st(1)
jmp .L2
.L1:
f2xm1
.L2:
.LGot2PowFracZM1:
fld1
faddp %st,%st(1)
fscale
fstp %st(1)
ret $12
.LFracOutOfRange:
jne .LForceZeroFrac { Safeguard against |frac(z)| ≥ 2, or Inf / NaN. If single(frac(z)) exponent is 0, 1 ≤ |frac(z)| < 2. }
{ Calculate 2**frac(z)-1 as N*(N+2), where N=2**(frac(z)/2)-1 }
fmuls half{$ifndef DISABLE_PIC_IN_EXP_REAL}-.LPIC(%ecx){$endif}
f2xm1
fld %st
fadds two{$ifndef DISABLE_PIC_IN_EXP_REAL}-.LPIC(%ecx){$endif}
fmulp %st,%st(1)
jmp .LGot2PowFracZM1
.LForceZeroFrac:
fstp %st
fld1
fscale
fstp %st(1)
end;