source: rtems/c/src/lib/libcpu/m68k/m68040/fpsp/x_snan.s @ f9b93da

//
//      x_snan.sa 3.3 7/1/91
//
// fpsp_snan --- FPSP handler for signalling NAN exception
//
// SNAN for float -> integer conversions (integer conversion of
// an SNAN) is a non-maskable run-time exception.
//
// For trap disabled the 040 does the following:
// If the dest data format is s, d, or x, then the SNAN bit in the NAN
// is set to one and the resulting non-signaling NAN (truncated if
// necessary) is transferred to the dest.  If the dest format is b, w,
// or l, then garbage is written to the dest (actually the upper 32 bits
// of the mantissa are sent to the integer unit).
//
// For trap enabled the 040 does the following:
// If the inst is move_out, then the results are the same as for trap 
// disabled with the exception posted.  If the instruction is not move_
// out, the dest. is not modified, and the exception is posted.
//

//              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//      THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 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_SNAN: //idnt    2,1 | Motorola 040 Floating Point Software Package

        |section        8

        .include "fpsp.defs"

        |xref   get_fline
        |xref   mem_write
        |xref   real_snan
        |xref   real_inex
        |xref   fpsp_done
        |xref   reg_dest

        .global fpsp_snan
fpsp_snan:
        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)

//
// Check if trap enabled
//
        btstb           #snan_bit,FPCR_ENABLE(%a6)
        bnes            ena             //If enabled, then branch

        bsrl            move_out        //else SNAN disabled
//
// It is possible to have an inex1 exception with the
// snan.  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
        beq     end_snan
//
// Inexact enabled and reported, and we must take an inexact exception.
//
take_inex:
        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
//
// SNAN is enabled.  Check if inst is move_out.
// Make any corrections to the 040 output as necessary.
//
ena:
        btstb           #5,CMDREG1B(%a6) //if set, inst is move out
        beq             not_out

        bsrl            move_out

report_snan:
        moveb           (%a7),VER_TMP(%a6)
        cmpib           #VER_40,(%a7)   //test for orig unimp frame
        bnes            ck_rev
        moveql          #13,%d0         //need to zero 14 lwords
        bras            rep_con
ck_rev:
        moveql          #11,%d0         //need to zero 12 lwords
rep_con:
        clrl            (%a7)
loop1:
        clrl            -(%a7)          //clear and dec a7
        dbra            %d0,loop1
        moveb           VER_TMP(%a6),(%a7) //format a busy frame
        moveb           #BUSY_SIZE-4,1(%a7)
        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            real_snan
//
// Exit snan handler by expanding the unimp frame into a busy frame
//
end_snan:
        bclrb           #E1,E_BYTE(%a6)

        moveb           (%a7),VER_TMP(%a6)
        cmpib           #VER_40,(%a7)   //test for orig unimp frame
        bnes            ck_rev2
        moveql          #13,%d0         //need to zero 14 lwords
        bras            rep_con2
ck_rev2:
        moveql          #11,%d0         //need to zero 12 lwords
rep_con2:
        clrl            (%a7)
loop2:
        clrl            -(%a7)          //clear and dec a7
        dbra            %d0,loop2
        moveb           VER_TMP(%a6),(%a7) //format a busy frame
        moveb           #BUSY_SIZE-4,1(%a7) //write busy size
        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

//
// Move_out 
//
move_out:
        movel           EXC_EA(%a6),%a0 //get <ea> from exc frame

        bfextu          CMDREG1B(%a6){#3:#3},%d0 //move rx field to d0{2:0}
        cmpil           #0,%d0          //check for long
        beqs            sto_long        //branch if move_out long
        
        cmpil           #4,%d0          //check for word
        beqs            sto_word        //branch if move_out word
        
        cmpil           #6,%d0          //check for byte
        beqs            sto_byte        //branch if move_out byte
        
//
// Not byte, word or long
//
        rts
//      
// Get the 32 most significant bits of etemp mantissa
//
sto_long:
        movel           ETEMP_HI(%a6),%d1
        movel           #4,%d0          //load byte count
//
// Set signalling nan bit
//
        bsetl           #30,%d1                 
//
// Store to the users destination address
//
        tstl            %a0             //check if <ea> is 0
        beqs            wrt_dn          //destination is a data register
        
        movel           %d1,-(%a7)      //move the snan onto the stack
        movel           %a0,%a1         //load dest addr into a1
        movel           %a7,%a0         //load src addr of snan into a0
        bsrl            mem_write       //write snan to user memory
        movel           (%a7)+,%d1      //clear off stack
        rts
//
// Get the 16 most significant bits of etemp mantissa
//
sto_word:
        movel           ETEMP_HI(%a6),%d1
        movel           #2,%d0          //load byte count
//
// Set signalling nan bit
//
        bsetl           #30,%d1                 
//
// Store to the users destination address
//
        tstl            %a0             //check if <ea> is 0
        beqs            wrt_dn          //destination is a data register

        movel           %d1,-(%a7)      //move the snan onto the stack
        movel           %a0,%a1         //load dest addr into a1
        movel           %a7,%a0         //point to low word
        bsrl            mem_write       //write snan to user memory
        movel           (%a7)+,%d1      //clear off stack
        rts
//
// Get the 8 most significant bits of etemp mantissa
//
sto_byte:
        movel           ETEMP_HI(%a6),%d1
        movel           #1,%d0          //load byte count
//
// Set signalling nan bit
//
        bsetl           #30,%d1                 
//
// Store to the users destination address
//
        tstl            %a0             //check if <ea> is 0
        beqs            wrt_dn          //destination is a data register
        movel           %d1,-(%a7)      //move the snan onto the stack
        movel           %a0,%a1         //load dest addr into a1
        movel           %a7,%a0         //point to source byte
        bsrl            mem_write       //write snan to user memory
        movel           (%a7)+,%d1      //clear off stack
        rts

//
//      wrt_dn --- write to a data register
//
//      We get here with D1 containing the data to write and D0 the
//      number of bytes to write: 1=byte,2=word,4=long.
//
wrt_dn:
        movel           %d1,L_SCR1(%a6) //data
        movel           %d0,-(%a7)      //size
        bsrl            get_fline       //returns fline word in d0
        movel           %d0,%d1
        andil           #0x7,%d1                //d1 now holds register number
        movel           (%sp)+,%d0      //get original size
        cmpil           #4,%d0
        beqs            wrt_long
        cmpil           #2,%d0
        bnes            wrt_byte
wrt_word:
        orl             #0x8,%d1
        bral            reg_dest
wrt_long:
        orl             #0x10,%d1
        bral            reg_dest
wrt_byte:
        bral            reg_dest
//
// Check if it is a src nan or dst nan
//
not_out:
        movel           DTAG(%a6),%d0   
        bfextu          %d0{#0:#3},%d0  //isolate dtag in lsbs

        cmpib           #3,%d0          //check for nan in destination
        bnes            issrc           //destination nan has priority
dst_nan:
        btstb           #6,FPTEMP_HI(%a6) //check if dest nan is an snan
        bnes            issrc           //no, so check source for snan
        movew           FPTEMP_EX(%a6),%d0
        bras            cont
issrc:
        movew           ETEMP_EX(%a6),%d0
cont:
        btstl           #15,%d0         //test for sign of snan
        beqs            clr_neg
        bsetb           #neg_bit,FPSR_CC(%a6)
        bra             report_snan
clr_neg:
        bclrb           #neg_bit,FPSR_CC(%a6)
        bra             report_snan

        |end