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|
; $Id: log2.asm $
;; @file
; IPRT - No-CRT log2 - AMD64 & X86.
;
;
; Copyright (C) 2006-2023 Oracle and/or its affiliates.
;
; This file is part of VirtualBox base platform packages, as
; available from https://www.virtualbox.org.
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation, in version 3 of the
; License.
;
; This program is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, see <https://www.gnu.org/licenses>.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
; in the VirtualBox distribution, in which case the provisions of the
; CDDL are applicable instead of those of the GPL.
;
; You may elect to license modified versions of this file under the
; terms and conditions of either the GPL or the CDDL or both.
;
; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
;
%define RT_ASM_WITH_SEH64
%include "iprt/asmdefs.mac"
%include "iprt/x86.mac"
BEGINCODE
extern NAME(RT_NOCRT(feraiseexcept))
;;
; Compute the log2 of rd
; @returns st(0) / xmm0
; @param rd [xSP + xCB*2] / xmm0
RT_NOCRT_BEGINPROC log2
push xBP
SEH64_PUSH_xBP
mov xBP, xSP
SEH64_SET_FRAME_xBP 0
sub xSP, 20h
SEH64_ALLOCATE_STACK 20h
SEH64_END_PROLOGUE
;
; Load the input into st0.
;
%ifdef RT_ARCH_AMD64
movsd [xBP - 10h], xmm0
fld qword [xBP - 10h]
%else
fld qword [xBP + xCB*2]
%endif
;
; Weed out non-normal values.
;
fxam
fnstsw ax
mov cx, ax
and ax, X86_FSW_C3 | X86_FSW_C2 | X86_FSW_C0
cmp ax, X86_FSW_C2 ; Normal finite number (excluding zero)
je .finite
cmp ax, X86_FSW_C3 ; Zero
je .zero
cmp ax, X86_FSW_C3 | X86_FSW_C2 ; Denormals
je .finite
cmp ax, X86_FSW_C0 | X86_FSW_C2 ; Infinity.
je .inf
jmp .nan
.finite:
; Negative number?
test cx, X86_FSW_C1
jnz .negative
; Is it +1.0?
fld1
fcomip st1
jz .plus_one
;
; The fyl2xp1 instruction (ST1=ST1*log2(ST0+1.0), popping ST0) has a
; valid ST0 range of 1(1-sqrt(0.5)) (approx 0.29289321881) on both
; sides of zero. We try use it if we can.
;
.above_one:
; For both fyl2xp1 and fyl2xp1 we need st1=1.0.
fld1
fxch st0, st1 ; -> st0=input; st1=1.0
; Check if the input is within the fyl2xp1 range.
fld qword [.s_r64AbsFyL2xP1InputMax xWrtRIP]
fcomip st0, st1
jbe .cannot_use_fyl2xp1
fld qword [.s_r64AbsFyL2xP1InputMin xWrtRIP]
fcomip st0, st1
jae .cannot_use_fyl2xp1
; Do the calculation.
.use_fyl2xp1:
fsub st0, st1 ; -> st0=input-1; st1=1.0
fyl2xp1 ; -> st0=1.0*log2(st0+1.0)
jmp .return_val
.cannot_use_fyl2xp1:
fyl2x ; -> st0=1.0*log2(st0)
;
; Return st0.
;
.return_val:
%ifdef RT_ARCH_AMD64
fstp qword [xBP - 10h]
movsd xmm0, [xBP - 10h]
%endif
.return:
leave
ret
;
; +1.0: Return +0.0.
;
.plus_one:
ffreep st0
fldz
jmp .return_val
;
; Negative numbers: Return NaN and raise invalid operation.
;
.negative:
.minus_inf:
; Raise invalid operation
%ifdef RT_ARCH_X86
mov dword [xSP], X86_FSW_IE
%elifdef ASM_CALL64_GCC
mov edi, X86_FSW_IE
%elifdef ASM_CALL64_MSC
mov ecx, X86_FSW_IE
%else
%error calling conv.
%endif
call NAME(RT_NOCRT(feraiseexcept))
; Load NaN
%ifdef RT_ARCH_AMD64
movsd xmm0, [.s_r64NaN xWrtRIP]
%else
fld qword [.s_r64NaN xWrtRIP]
%endif
jmp .return
;
; +/-0.0: Return inf and raise divide by zero error.
;
.zero:
ffreep st0
; Raise div/0
%ifdef RT_ARCH_X86
mov dword [xSP], X86_FSW_ZE
%elifdef ASM_CALL64_GCC
mov edi, X86_FSW_ZE
%elifdef ASM_CALL64_MSC
mov ecx, X86_FSW_ZE
%else
%error calling conv.
%endif
call NAME(RT_NOCRT(feraiseexcept))
; Load +Inf
%ifdef RT_ARCH_AMD64
movsd xmm0, [.s_r64MinusInf xWrtRIP]
%else
fld qword [.s_r64MinusInf xWrtRIP]
%endif
jmp .return
;
; -Inf: Same as other negative numbers
; +Inf: return +Inf. Join path with NaN.
;
.inf:
test cx, X86_FSW_C1 ; sign bit
jnz .minus_inf
;
; NaN: Return the input NaN value as is, if we can.
;
.nan:
%ifdef RT_ARCH_AMD64
ffreep st0
%endif
jmp .return
ALIGNCODE(8)
;; The fyl2xp1 instruction only works between +/-1(1-sqrt(0.5)).
; These two variables is that range + 1.0, so we can compare directly
; with the input w/o any extra fsub and fabs work.
.s_r64AbsFyL2xP1InputMin:
dq 0.708 ; -0.292 + 1.0
.s_r64AbsFyL2xP1InputMax:
dq 1.292
;.s_r64AbsFyL2xP1Range:
; dq 0.292
.s_r64MinusInf:
dq RTFLOAT64U_INF_MINUS
.s_r64NaN:
dq RTFLOAT64U_QNAN_MINUS
ENDPROC RT_NOCRT(log2)
|
