* 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
*..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
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
