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|
* $OpenBSD: srem_mod.sa,v 1.2 1996/05/29 21:05:41 niklas Exp $
* $NetBSD: srem_mod.sa,v 1.3 1994/10/26 07:49:58 cgd Exp $
* MOTOROLA MICROPROCESSOR & MEMORY TECHNOLOGY GROUP
* M68000 Hi-Performance Microprocessor Division
* M68040 Software Package
*
* M68040 Software Package Copyright (c) 1993, 1994 Motorola Inc.
* All rights reserved.
*
* THE SOFTWARE is provided on an "AS IS" basis and without warranty.
* To the maximum extent permitted by applicable law,
* MOTOROLA DISCLAIMS ALL WARRANTIES WHETHER EXPRESS OR IMPLIED,
* INCLUDING IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
* PARTICULAR PURPOSE and any warranty against infringement with
* regard to the SOFTWARE (INCLUDING ANY MODIFIED VERSIONS THEREOF)
* and any accompanying written materials.
*
* To the maximum extent permitted by applicable law,
* IN NO EVENT SHALL MOTOROLA BE LIABLE FOR ANY DAMAGES WHATSOEVER
* (INCLUDING WITHOUT LIMITATION, DAMAGES FOR LOSS OF BUSINESS
* PROFITS, BUSINESS INTERRUPTION, LOSS OF BUSINESS INFORMATION, OR
* OTHER PECUNIARY LOSS) ARISING OF THE USE OR INABILITY TO USE THE
* SOFTWARE. Motorola assumes no responsibility for the maintenance
* and support of the SOFTWARE.
*
* You are hereby granted a copyright license to use, modify, and
* distribute the SOFTWARE so long as this entire notice is retained
* without alteration in any modified and/or redistributed versions,
* and that such modified versions are clearly identified as such.
* No licenses are granted by implication, estoppel or otherwise
* under any patents or trademarks of Motorola, Inc.
*
* srem_mod.sa 3.1 12/10/90
*
* The entry point sMOD computes the floating point MOD of the
* input values X and Y. The entry point sREM computes the floating
* point (IEEE) REM of the input values X and Y.
*
* INPUT
* -----
* Double-extended value Y is pointed to by address in register
* A0. Double-extended value X is located in -12(A0). The values
* of X and Y are both nonzero and finite; although either or both
* of them can be denormalized. The special cases of zeros, NaNs,
* and infinities are handled elsewhere.
*
* OUTPUT
* ------
* FREM(X,Y) or FMOD(X,Y), depending on entry point.
*
* ALGORITHM
* ---------
*
* Step 1. Save and strip signs of X and Y: signX := sign(X),
* signY := sign(Y), X := |X|, Y := |Y|,
* signQ := signX EOR signY. Record whether MOD or REM
* is requested.
*
* Step 2. Set L := expo(X)-expo(Y), k := 0, Q := 0.
* If (L < 0) then
* R := X, go to Step 4.
* else
* R := 2^(-L)X, j := L.
* endif
*
* Step 3. Perform MOD(X,Y)
* 3.1 If R = Y, go to Step 9.
* 3.2 If R > Y, then { R := R - Y, Q := Q + 1}
* 3.3 If j = 0, go to Step 4.
* 3.4 k := k + 1, j := j - 1, Q := 2Q, R := 2R. Go to
* Step 3.1.
*
* Step 4. At this point, R = X - QY = MOD(X,Y). Set
* Last_Subtract := false (used in Step 7 below). If
* MOD is requested, go to Step 6.
*
* Step 5. R = MOD(X,Y), but REM(X,Y) is requested.
* 5.1 If R < Y/2, then R = MOD(X,Y) = REM(X,Y). Go to
* Step 6.
* 5.2 If R > Y/2, then { set Last_Subtract := true,
* Q := Q + 1, Y := signY*Y }. Go to Step 6.
* 5.3 This is the tricky case of R = Y/2. If Q is odd,
* then { Q := Q + 1, signX := -signX }.
*
* Step 6. R := signX*R.
*
* Step 7. If Last_Subtract = true, R := R - Y.
*
* Step 8. Return signQ, last 7 bits of Q, and R as required.
*
* Step 9. At this point, R = 2^(-j)*X - Q Y = Y. Thus,
* X = 2^(j)*(Q+1)Y. set Q := 2^(j)*(Q+1),
* R := 0. Return signQ, last 7 bits of Q, and R.
*
SREM_MOD IDNT 2,1 Motorola 040 Floating Point Software Package
section 8
include fpsp.h
Mod_Flag equ L_SCR3
SignY equ FP_SCR3+4
SignX equ FP_SCR3+8
SignQ equ FP_SCR3+12
Sc_Flag equ FP_SCR4
Y equ FP_SCR1
Y_Hi equ Y+4
Y_Lo equ Y+8
R equ FP_SCR2
R_Hi equ R+4
R_Lo equ R+8
Scale DC.L $00010000,$80000000,$00000000,$00000000
xref t_avoid_unsupp
xdef smod
smod:
Clr.L Mod_Flag(a6)
BRA.B Mod_Rem
xdef srem
srem:
Move.L #1,Mod_Flag(a6)
Mod_Rem:
*..Save sign of X and Y
MoveM.L D2-D7,-(A7) ...save data registers
Move.W (A0),D3
Move.W D3,SignY(a6)
AndI.L #$00007FFF,D3 ...Y := |Y|
*
Move.L 4(A0),D4
Move.L 8(A0),D5 ...(D3,D4,D5) is |Y|
Tst.L D3
BNE.B Y_Normal
Move.L #$00003FFE,D3 ...$3FFD + 1
Tst.L D4
BNE.B HiY_not0
HiY_0:
Move.L D5,D4
CLR.L D5
SubI.L #32,D3
CLR.L D6
BFFFO D4{0:32},D6
LSL.L D6,D4
Sub.L D6,D3 ...(D3,D4,D5) is normalized
* ...with bias $7FFD
BRA.B Chk_X
HiY_not0:
CLR.L D6
BFFFO D4{0:32},D6
Sub.L D6,D3
LSL.L D6,D4
Move.L D5,D7 ...a copy of D5
LSL.L D6,D5
Neg.L D6
AddI.L #32,D6
LSR.L D6,D7
Or.L D7,D4 ...(D3,D4,D5) normalized
* ...with bias $7FFD
BRA.B Chk_X
Y_Normal:
AddI.L #$00003FFE,D3 ...(D3,D4,D5) normalized
* ...with bias $7FFD
Chk_X:
Move.W -12(A0),D0
Move.W D0,SignX(a6)
Move.W SignY(a6),D1
EOr.L D0,D1
AndI.L #$00008000,D1
Move.W D1,SignQ(a6) ...sign(Q) obtained
AndI.L #$00007FFF,D0
Move.L -8(A0),D1
Move.L -4(A0),D2 ...(D0,D1,D2) is |X|
Tst.L D0
BNE.B X_Normal
Move.L #$00003FFE,D0
Tst.L D1
BNE.B HiX_not0
HiX_0:
Move.L D2,D1
CLR.L D2
SubI.L #32,D0
CLR.L D6
BFFFO D1{0:32},D6
LSL.L D6,D1
Sub.L D6,D0 ...(D0,D1,D2) is normalized
* ...with bias $7FFD
BRA.B Init
HiX_not0:
CLR.L D6
BFFFO D1{0:32},D6
Sub.L D6,D0
LSL.L D6,D1
Move.L D2,D7 ...a copy of D2
LSL.L D6,D2
Neg.L D6
AddI.L #32,D6
LSR.L D6,D7
Or.L D7,D1 ...(D0,D1,D2) normalized
* ...with bias $7FFD
BRA.B Init
X_Normal:
AddI.L #$00003FFE,D0 ...(D0,D1,D2) normalized
* ...with bias $7FFD
Init:
*
Move.L D3,L_SCR1(a6) ...save biased expo(Y)
move.l d0,L_SCR2(a6) ;save d0
Sub.L D3,D0 ...L := expo(X)-expo(Y)
* Move.L D0,L ...D0 is j
CLR.L D6 ...D6 := carry <- 0
CLR.L D3 ...D3 is Q
MoveA.L #0,A1 ...A1 is k; j+k=L, Q=0
*..(Carry,D1,D2) is R
Tst.L D0
BGE.B Mod_Loop
*..expo(X) < expo(Y). Thus X = mod(X,Y)
*
move.l L_SCR2(a6),d0 ;restore d0
BRA.W Get_Mod
*..At this point R = 2^(-L)X; Q = 0; k = 0; and k+j = L
Mod_Loop:
Tst.L D6 ...test carry bit
BGT.B R_GT_Y
*..At this point carry = 0, R = (D1,D2), Y = (D4,D5)
Cmp.L D4,D1 ...compare hi(R) and hi(Y)
BNE.B R_NE_Y
Cmp.L D5,D2 ...compare lo(R) and lo(Y)
BNE.B R_NE_Y
*..At this point, R = Y
BRA.W Rem_is_0
R_NE_Y:
*..use the borrow of the previous compare
BCS.B R_LT_Y ...borrow is set iff R < Y
R_GT_Y:
*..If Carry is set, then Y < (Carry,D1,D2) < 2Y. Otherwise, Carry = 0
*..and Y < (D1,D2) < 2Y. Either way, perform R - Y
Sub.L D5,D2 ...lo(R) - lo(Y)
SubX.L D4,D1 ...hi(R) - hi(Y)
CLR.L D6 ...clear carry
AddQ.L #1,D3 ...Q := Q + 1
R_LT_Y:
*..At this point, Carry=0, R < Y. R = 2^(k-L)X - QY; k+j = L; j >= 0.
Tst.L D0 ...see if j = 0.
BEQ.B PostLoop
Add.L D3,D3 ...Q := 2Q
Add.L D2,D2 ...lo(R) = 2lo(R)
AddX.L D1,D1 ...hi(R) = 2hi(R) + carry
SCS D6 ...set Carry if 2(R) overflows
AddQ.L #1,A1 ...k := k+1
SubQ.L #1,D0 ...j := j - 1
*..At this point, R=(Carry,D1,D2) = 2^(k-L)X - QY, j+k=L, j >= 0, R < 2Y.
BRA.B Mod_Loop
PostLoop:
*..k = L, j = 0, Carry = 0, R = (D1,D2) = X - QY, R < Y.
*..normalize R.
Move.L L_SCR1(a6),D0 ...new biased expo of R
Tst.L D1
BNE.B HiR_not0
HiR_0:
Move.L D2,D1
CLR.L D2
SubI.L #32,D0
CLR.L D6
BFFFO D1{0:32},D6
LSL.L D6,D1
Sub.L D6,D0 ...(D0,D1,D2) is normalized
* ...with bias $7FFD
BRA.B Get_Mod
HiR_not0:
CLR.L D6
BFFFO D1{0:32},D6
BMI.B Get_Mod ...already normalized
Sub.L D6,D0
LSL.L D6,D1
Move.L D2,D7 ...a copy of D2
LSL.L D6,D2
Neg.L D6
AddI.L #32,D6
LSR.L D6,D7
Or.L D7,D1 ...(D0,D1,D2) normalized
*
Get_Mod:
CmpI.L #$000041FE,D0
BGE.B No_Scale
Do_Scale:
Move.W D0,R(a6)
clr.w R+2(a6)
Move.L D1,R_Hi(a6)
Move.L D2,R_Lo(a6)
Move.L L_SCR1(a6),D6
Move.W D6,Y(a6)
clr.w Y+2(a6)
Move.L D4,Y_Hi(a6)
Move.L D5,Y_Lo(a6)
FMove.X R(a6),fp0 ...no exception
Move.L #1,Sc_Flag(a6)
BRA.B ModOrRem
No_Scale:
Move.L D1,R_Hi(a6)
Move.L D2,R_Lo(a6)
SubI.L #$3FFE,D0
Move.W D0,R(a6)
clr.w R+2(a6)
Move.L L_SCR1(a6),D6
SubI.L #$3FFE,D6
Move.L D6,L_SCR1(a6)
FMove.X R(a6),fp0
Move.W D6,Y(a6)
Move.L D4,Y_Hi(a6)
Move.L D5,Y_Lo(a6)
Clr.L Sc_Flag(a6)
*
ModOrRem:
Move.L Mod_Flag(a6),D6
BEQ.B Fix_Sign
Move.L L_SCR1(a6),D6 ...new biased expo(Y)
SubQ.L #1,D6 ...biased expo(Y/2)
Cmp.L D6,D0
BLT.B Fix_Sign
BGT.B Last_Sub
Cmp.L D4,D1
BNE.B Not_EQ
Cmp.L D5,D2
BNE.B Not_EQ
BRA.W Tie_Case
Not_EQ:
BCS.B Fix_Sign
Last_Sub:
*
FSub.X Y(a6),fp0 ...no exceptions
AddQ.L #1,D3 ...Q := Q + 1
*
Fix_Sign:
*..Get sign of X
Move.W SignX(a6),D6
BGE.B Get_Q
FNeg.X fp0
*..Get Q
*
Get_Q:
clr.l d6
Move.W SignQ(a6),D6 ...D6 is sign(Q)
Move.L #8,D7
LSR.L D7,D6
AndI.L #$0000007F,D3 ...7 bits of Q
Or.L D6,D3 ...sign and bits of Q
Swap D3
FMove.L fpsr,D6
AndI.L #$FF00FFFF,D6
Or.L D3,D6
FMove.L D6,fpsr ...put Q in fpsr
*
Restore:
MoveM.L (A7)+,D2-D7
FMove.L USER_FPCR(a6),fpcr
Move.L Sc_Flag(a6),D0
BEQ.B Finish
FMul.X Scale(pc),fp0 ...may cause underflow
bra t_avoid_unsupp ;check for denorm as a
* ;result of the scaling
Finish:
fmove.x fp0,fp0 ;capture exceptions & round
rts
Rem_is_0:
*..R = 2^(-j)X - Q Y = Y, thus R = 0 and quotient = 2^j (Q+1)
AddQ.L #1,D3
CmpI.L #8,D0 ...D0 is j
BGE.B Q_Big
LSL.L D0,D3
BRA.B Set_R_0
Q_Big:
CLR.L D3
Set_R_0:
FMove.S #:00000000,fp0
Clr.L Sc_Flag(a6)
BRA.W Fix_Sign
Tie_Case:
*..Check parity of Q
Move.L D3,D6
AndI.L #$00000001,D6
Tst.L D6
BEq.W Fix_Sign ...Q is even
*..Q is odd, Q := Q + 1, signX := -signX
AddQ.L #1,D3
Move.W SignX(a6),D6
EOrI.L #$00008000,D6
Move.W D6,SignX(a6)
BRA.W Fix_Sign
End
|
