subttl    emfconst.asm - Loading of 387 on chip constants
        page

;emfconst.asm - Loading of 387 on chip constants

;        Microsoft Confidential

;     Copyright (c) Microsoft Corporation 1991
;        All Rights Reserved

;Purpose:
;       FLDZ, FLD1, FLDPI, FLDL2T, FLDL2E, FLDLG2, FLDLN2 instructions
;Inputs:
;    edi = [CURstk]

;Revision History:

; []    09/05/91  TP    Initial 32-bit version.




    PrevStackWrap    edi,Ld1        ;Tied to PrevStackElem below

EM_ENTRY eFLD1
eFLD1:
;edi = [CURstk]
    PrevStackElem    edi,Ld1        ;Point to receiving location
    cmp    EMSEG:[edi].bTag,bTAG_EMPTY    ;Is it empty?
    jnz    FldErr            ;in emload.asm
    mov    EMSEG:[CURstk],edi
    mov    EMSEG:[edi].lManLo,0
    mov    EMSEG:[edi].lManHi,1 shl 31
    mov    EMSEG:[edi].ExpSgn,bTAG_SNGL    ;Exponent and sign are zero
    ret


    PrevStackWrap    edi,Ldz        ;Tied to PrevStackElem below

EM_ENTRY eFLDZ
eFLDZ:
;edi = [CURstk]
    PrevStackElem    edi,Ldz        ;Point to receiving location
    cmp    EMSEG:[edi].bTag,bTAG_EMPTY    ;Is it empty?
    jnz    FldErr            ;in emload.asm
    mov    EMSEG:[CURstk],edi
    mov    EMSEG:[edi].lManLo,0
    mov    EMSEG:[edi].lManHi,0
    mov    EMSEG:[edi].ExpSgn,bTAG_ZERO    ;Exponent and sign are zero
    ret



;The 5 irrational constants need to be adjusted according to rounding mode.

DefConst    macro    cName,low,high,expon,round
c&cName&lo    equ    low
c&cName&hi    equ    high
c&cName&exp     equ     expon
c&cName&rnd     equ     round
    endm

DefConst    FLDL2T,0CD1B8AFEH,0D49A784BH,00001H,0

DefConst    FLDL2E,05C17F0BCH,0B8AA3B29H,00000H,1

DefConst    FLDLG2,0FBCFF799H,09A209A84H,0FFFEH,1

DefConst    FLDLN2,0D1CF79ACH,0B17217F7H,0FFFFH,1

DefConst    FLDPI,02168C235H,0C90FDAA2H,00001H,1


LoadConstant   macro   cName,nojmp
EM_ENTRY e&cName
e&cName:
    mov    ebx,c&cName&hi
    mov    edx,c&cName&lo
        mov     ecx,c&cName&exp shl 16 + c&cName&rnd
ifb    <nojmp>
    jmp    CommonConst
endif
    endm

LoadConstant    FLDL2T

LoadConstant    FLDL2E

LoadConstant    FLDLG2

LoadConstant    FLDLN2

LoadConstant    FLDPI,nojmp

CommonConst:
;ebx:edx = mantissa of constant, rounded to nearest
;high ecx = exponent
;ch = sign
;cl = rounding flag: 1 indicates roundup occured for round nearest, else 0
;edi = [CURstk]
    test    EMSEG:[CWcntl],RoundControl    ;Check rounding control bits
.erre    RCnear eq 0
    jnz    NotNearConst        ;Adjust constant if not round nearest
StoreConst:
    mov    cl,bTAG_VALID
    mov    esi,edx
    jmp    FldCont            ;In emload.asm

NotNearConst:
;It is known that the five constants positive irrational numbers.
;This means they are never exact, and chop and round down always
;produce the same answer.  It is also know that the values are such
;that rounding only alters bits in the last byte.

;A flag in cl indicates if the number has been rounded up for round
;nearest (1 = rounded up, 0 = rounded down).  In chop and round down
;modes, this flag can be directly subtracted to reverse the rounding.
;In round up mode, we want to add (1-flag) = -(flag-1).
.erre    RCchop eq 0CH            ;Two bits set only for chop
    test    EMSEG:[CWcntl],RCdown    ;DOWN bit set?
    jnz    DirectRoundConst    ;If so, it's chop or down
;Round Up mode
    dec    cl            ;-1 if round up needed, else 0
DirectRoundConst:
    sub    dl,cl            ;Directed rounding
    jmp    StoreConst