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//
//      $Id: x_unfl.S,v 1.2 2001-09-27 12:01:22 chris Exp $
//
//      x_unfl.sa 3.4 7/1/91
//
//      fpsp_unfl --- FPSP handler for underflow exception
//
// Trap disabled results
//      For 881/2 compatibility, sw must denormalize the intermediate 
// result, then store the result.  Denormalization is accomplished 
// by taking the intermediate result (which is always normalized) and 
// shifting the mantissa right while incrementing the exponent until 
// it is equal to the denormalized exponent for the destination 
// format.  After denormalization, the result is rounded to the 
// destination format.
//              
// Trap enabled results
//      All trap disabled code applies. In addition the exceptional 
// operand needs to made available to the user with a bias of $6000 
// added to the exponent.
//

//              Copyright (C) Motorola, Inc. 1990
//                      All Rights Reserved
//
//      THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
//      The copyright notice above does not evidence any  
//      actual or intended publication of such source code.

X_UNFL: //idnt    2,1 | Motorola 040 Floating Point Software Package

        |section        8

#include "fpsp.defs"

        |xref   denorm
        |xref   round
        |xref   store
        |xref   g_rndpr
        |xref   g_opcls
        |xref   g_dfmtou
        |xref   real_unfl
        |xref   real_inex
        |xref   fpsp_done
        |xref   b1238_fix

        .global fpsp_unfl
fpsp_unfl:
        link            %a6,#-LOCAL_SIZE
        fsave           -(%a7)
        moveml          %d0-%d1/%a0-%a1,USER_DA(%a6)
        fmovemx %fp0-%fp3,USER_FP0(%a6)
        fmoveml %fpcr/%fpsr/%fpiar,USER_FPCR(%a6)

//
        bsrl            unf_res //denormalize, round & store interm op
//
// If underflow exceptions are not enabled, check for inexact
// exception
//
        btstb           #unfl_bit,FPCR_ENABLE(%a6)
        beqs            ck_inex

        btstb           #E3,E_BYTE(%a6)
        beqs            no_e3_1
//
// Clear dirty bit on dest resister in the frame before branching
// to b1238_fix.
//
        bfextu          CMDREG3B(%a6){#6:#3},%d0        //get dest reg no
        bclrb           %d0,FPR_DIRTY_BITS(%a6) //clr dest dirty bit
        bsrl            b1238_fix               //test for bug1238 case
        movel           USER_FPSR(%a6),FPSR_SHADOW(%a6)
        orl             #sx_mask,E_BYTE(%a6)
no_e3_1:
        moveml          USER_DA(%a6),%d0-%d1/%a0-%a1
        fmovemx USER_FP0(%a6),%fp0-%fp3
        fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
        frestore        (%a7)+
        unlk            %a6
        bral            real_unfl
//
// It is possible to have either inex2 or inex1 exceptions with the
// unfl.  If the inex enable bit is set in the FPCR, and either
// inex2 or inex1 occurred, we must clean up and branch to the
// real inex handler.
//
ck_inex:
        moveb           FPCR_ENABLE(%a6),%d0
        andb            FPSR_EXCEPT(%a6),%d0
        andib           #0x3,%d0
        beqs            unfl_done

//
// Inexact enabled and reported, and we must take an inexact exception
//      
take_inex:
        btstb           #E3,E_BYTE(%a6)
        beqs            no_e3_2
//
// Clear dirty bit on dest resister in the frame before branching
// to b1238_fix.
//
        bfextu          CMDREG3B(%a6){#6:#3},%d0        //get dest reg no
        bclrb           %d0,FPR_DIRTY_BITS(%a6) //clr dest dirty bit
        bsrl            b1238_fix               //test for bug1238 case
        movel           USER_FPSR(%a6),FPSR_SHADOW(%a6)
        orl             #sx_mask,E_BYTE(%a6)
no_e3_2:
        moveb           #INEX_VEC,EXC_VEC+1(%a6)
        moveml         USER_DA(%a6),%d0-%d1/%a0-%a1
        fmovemx        USER_FP0(%a6),%fp0-%fp3
        fmoveml        USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
        frestore        (%a7)+
        unlk            %a6
        bral            real_inex

unfl_done:
        bclrb           #E3,E_BYTE(%a6)
        beqs            e1_set          //if set then branch
//
// Clear dirty bit on dest resister in the frame before branching
// to b1238_fix.
//
        bfextu          CMDREG3B(%a6){#6:#3},%d0                //get dest reg no
        bclrb           %d0,FPR_DIRTY_BITS(%a6) //clr dest dirty bit
        bsrl            b1238_fix               //test for bug1238 case
        movel           USER_FPSR(%a6),FPSR_SHADOW(%a6)
        orl             #sx_mask,E_BYTE(%a6)
        moveml          USER_DA(%a6),%d0-%d1/%a0-%a1
        fmovemx USER_FP0(%a6),%fp0-%fp3
        fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
        frestore        (%a7)+
        unlk            %a6
        bral            fpsp_done
e1_set:
        moveml          USER_DA(%a6),%d0-%d1/%a0-%a1
        fmovemx USER_FP0(%a6),%fp0-%fp3
        fmoveml USER_FPCR(%a6),%fpcr/%fpsr/%fpiar
        unlk            %a6
        bral            fpsp_done
//
//      unf_res --- underflow result calculation
//
unf_res:
        bsrl            g_rndpr         //returns RND_PREC in d0 0=ext,
//                                      ;1=sgl, 2=dbl
//                                      ;we need the RND_PREC in the
//                                      ;upper word for round
        movew           #0,-(%a7)       
        movew           %d0,-(%a7)      //copy RND_PREC to stack
//
//
// If the exception bit set is E3, the exceptional operand from the
// fpu is in WBTEMP; else it is in FPTEMP.
//
        btstb           #E3,E_BYTE(%a6)
        beqs            unf_E1
unf_E3:
        lea             WBTEMP(%a6),%a0 //a0 now points to operand
//
// Test for fsgldiv and fsglmul.  If the inst was one of these, then
// force the precision to extended for the denorm routine.  Use
// the user's precision for the round routine.
//
        movew           CMDREG3B(%a6),%d1       //check for fsgldiv or fsglmul
        andiw           #0x7f,%d1
        cmpiw           #0x30,%d1               //check for sgldiv
        beqs            unf_sgl
        cmpiw           #0x33,%d1               //check for sglmul
        bnes            unf_cont        //if not, use fpcr prec in round
unf_sgl:
        clrl            %d0
        movew           #0x1,(%a7)      //override g_rndpr precision
//                                      ;force single
        bras            unf_cont
unf_E1:
        lea             FPTEMP(%a6),%a0 //a0 now points to operand
unf_cont:
        bclrb           #sign_bit,LOCAL_EX(%a0) //clear sign bit
        sne             LOCAL_SGN(%a0)          //store sign

        bsrl            denorm          //returns denorm, a0 points to it
//
// WARNING:
//                              ;d0 has guard,round sticky bit
//                              ;make sure that it is not corrupted
//                              ;before it reaches the round subroutine
//                              ;also ensure that a0 isn't corrupted

//
// Set up d1 for round subroutine d1 contains the PREC/MODE
// information respectively on upper/lower register halves.
//
        bfextu          FPCR_MODE(%a6){#2:#2},%d1       //get mode from FPCR
//                                              ;mode in lower d1
        addl            (%a7)+,%d1              //merge PREC/MODE
//
// WARNING: a0 and d0 are assumed to be intact between the denorm and
// round subroutines. All code between these two subroutines
// must not corrupt a0 and d0.
//
//
// Perform Round        
//      Input:          a0 points to input operand
//                      d0{31:29} has guard, round, sticky
//                      d1{01:00} has rounding mode
//                      d1{17:16} has rounding precision
//      Output:         a0 points to rounded operand
//

        bsrl            round           //returns rounded denorm at (a0)
//
// Differentiate between store to memory vs. store to register
//
unf_store:
        bsrl            g_opcls         //returns opclass in d0{2:0}
        cmpib           #0x3,%d0
        bnes            not_opc011
//
// At this point, a store to memory is pending
//
opc011:
        bsrl            g_dfmtou
        tstb            %d0
        beqs            ext_opc011      //If extended, do not subtract
//                              ;If destination format is sgl/dbl, 
        tstb            LOCAL_HI(%a0)   //If rounded result is normal,don't
//                                      ;subtract
        bmis            ext_opc011
        subqw           #1,LOCAL_EX(%a0)        //account for denorm bias vs.
//                              ;normalized bias
//                              ;          normalized   denormalized
//                              ;single       $7f           $7e
//                              ;double       $3ff          $3fe
//
ext_opc011:
        bsrl            store           //stores to memory
        bras            unf_done        //finish up

//
// At this point, a store to a float register is pending
//
not_opc011:
        bsrl            store   //stores to float register
//                              ;a0 is not corrupted on a store to a
//                              ;float register.
//
// Set the condition codes according to result
//
        tstl            LOCAL_HI(%a0)   //check upper mantissa
        bnes            ck_sgn
        tstl            LOCAL_LO(%a0)   //check lower mantissa
        bnes            ck_sgn
        bsetb           #z_bit,FPSR_CC(%a6) //set condition codes if zero
ck_sgn:
        btstb           #sign_bit,LOCAL_EX(%a0) //check the sign bit
        beqs            unf_done
        bsetb           #neg_bit,FPSR_CC(%a6)

//
// Finish.  
//
unf_done:
        btstb           #inex2_bit,FPSR_EXCEPT(%a6)
        beqs            no_aunfl
        bsetb           #aunfl_bit,FPSR_AEXCEPT(%a6)
no_aunfl:
        rts

        |end